A Starting Point for Investigation: /sys/power/state and /sys/power/disk These two system files exist to allow debugging of hibernation, and thus control the exact state used directly. Writing specific values to the state file controls the exact sleep mode used and disk controls the specific hibernation mode¹. This is extremely handy as an entry point to understand how these systems work, since we can just follow what happens when they are written to.

Show and Store Functions These two files are defined using the power_attr macro: kernel/power/power.h:80

#define power_attr(_name) \
static struct kobj_attribute _name##_attr =     \
    .attr   =               \
        .name = __stringify(_name), \
        .mode = 0644,           \
     ,                  \
    .show   = _name##_show,         \
    .store  = _name##_store,        \
 

show is called on reads and store on writes. state_show is a little boring for our purposes, as it just prints all the available sleep states. kernel/power/main.c:657

/*
 * state - control system sleep states.
 *
 * show() returns available sleep state labels, which may be "mem", "standby",
 * "freeze" and "disk" (hibernation).
 * See Documentation/admin-guide/pm/sleep-states.rst for a description of
 * what they mean.
 *
 * store() accepts one of those strings, translates it into the proper
 * enumerated value, and initiates a suspend transition.
 */
static ssize_t state_show(struct kobject *kobj, struct kobj_attribute *attr,
			  char *buf)
 
	char *s = buf;
#ifdef CONFIG_SUSPEND
	suspend_state_t i;
	for (i = PM_SUSPEND_MIN; i < PM_SUSPEND_MAX; i++)
		if (pm_states[i])
			s += sprintf(s,"%s ", pm_states[i]);
#endif
	if (hibernation_available())
		s += sprintf(s, "disk ");
	if (s != buf)
		/* convert the last space to a newline */
		*(s-1) = '\n';
	return (s - buf);
 

state_store, however, provides our entry point. If the string disk is written to the state file, it calls hibernate(). This is our entry point. kernel/power/main.c:715

static ssize_t state_store(struct kobject *kobj, struct kobj_attribute *attr,
			   const char *buf, size_t n)
 
	suspend_state_t state;
	int error;
	error = pm_autosleep_lock();
	if (error)
		return error;
	if (pm_autosleep_state() > PM_SUSPEND_ON)  
		error = -EBUSY;
		goto out;
	 
	state = decode_state(buf, n);
	if (state < PM_SUSPEND_MAX)  
		if (state == PM_SUSPEND_MEM)
			state = mem_sleep_current;
		error = pm_suspend(state);
	  else if (state == PM_SUSPEND_MAX)  
		error = hibernate();
	  else  
		error = -EINVAL;
	 
 out:
	pm_autosleep_unlock();
	return error ? error : n;
 

kernel/power/main.c:688

static suspend_state_t decode_state(const char *buf, size_t n)
 
#ifdef CONFIG_SUSPEND
	suspend_state_t state;
#endif
	char *p;
	int len;
	p = memchr(buf, '\n', n);
	len = p ? p - buf : n;
	/* Check hibernation first. */
	if (len == 4 && str_has_prefix(buf, "disk"))
		return PM_SUSPEND_MAX;
#ifdef CONFIG_SUSPEND
	for (state = PM_SUSPEND_MIN; state < PM_SUSPEND_MAX; state++)  
		const char *label = pm_states[state];
		if (label && len == strlen(label) && !strncmp(buf, label, len))
			return state;
	 
#endif
	return PM_SUSPEND_ON;
 

Could we have figured this out just via function names? Sure, but this way we know for sure that nothing else is happening before this function is called.

Autosleep Our first detour is into the autosleep system. When checking the state above, you may notice that the kernel grabs the pm_autosleep_lock before checking the current state. autosleep is a mechanism originally from Android that sends the entire system to either suspend or hibernate whenever it is not actively working on anything. This is not enabled for most desktop configurations, since it s primarily for mobile systems and inverts the standard suspend and hibernate interactions. This system is implemented as a workqueue² that checks the current number of wakeup events, processes and drivers that need to run³, and if there aren t any, then the system is put into the autosleep state, typically suspend. However, it could be hibernate if configured that way via /sys/power/autosleep in a similar manner to using /sys/power/state to manually enable hibernation. kernel/power/main.c:841

static ssize_t autosleep_store(struct kobject *kobj,
			       struct kobj_attribute *attr,
			       const char *buf, size_t n)
 
	suspend_state_t state = decode_state(buf, n);
	int error;
	if (state == PM_SUSPEND_ON
	    && strcmp(buf, "off") && strcmp(buf, "off\n"))
		return -EINVAL;
	if (state == PM_SUSPEND_MEM)
		state = mem_sleep_current;
	error = pm_autosleep_set_state(state);
	return error ? error : n;
 
power_attr(autosleep);
#endif /* CONFIG_PM_AUTOSLEEP */

kernel/power/autosleep.c:24

static DEFINE_MUTEX(autosleep_lock);
static struct wakeup_source *autosleep_ws;
static void try_to_suspend(struct work_struct *work)
 
	unsigned int initial_count, final_count;
	if (!pm_get_wakeup_count(&initial_count, true))
		goto out;
	mutex_lock(&autosleep_lock);
	if (!pm_save_wakeup_count(initial_count)  
		system_state != SYSTEM_RUNNING)  
		mutex_unlock(&autosleep_lock);
		goto out;
	 
	if (autosleep_state == PM_SUSPEND_ON)  
		mutex_unlock(&autosleep_lock);
		return;
	 
	if (autosleep_state >= PM_SUSPEND_MAX)
		hibernate();
	else
		pm_suspend(autosleep_state);
	mutex_unlock(&autosleep_lock);
	if (!pm_get_wakeup_count(&final_count, false))
		goto out;
	/*
	 * If the wakeup occurred for an unknown reason, wait to prevent the
	 * system from trying to suspend and waking up in a tight loop.
	 */
	if (final_count == initial_count)
		schedule_timeout_uninterruptible(HZ / 2);
 out:
	queue_up_suspend_work();
 
static DECLARE_WORK(suspend_work, try_to_suspend);
void queue_up_suspend_work(void)
 
	if (autosleep_state > PM_SUSPEND_ON)
		queue_work(autosleep_wq, &suspend_work);
 

The Steps of Hibernation

Hibernation Kernel Config It s important to note that most of the hibernate-specific functions below do nothing unless you ve defined CONFIG_HIBERNATION in your Kconfig⁴. As an example, hibernate itself is defined as the following if CONFIG_HIBERNATE is not set. include/linux/suspend.h:407

static inline int hibernate(void)   return -ENOSYS;  

Check if Hibernation is Available We begin by confirming that we actually can perform hibernation, via the hibernation_available function. kernel/power/hibernate.c:742

if (!hibernation_available())  
	pm_pr_dbg("Hibernation not available.\n");
	return -EPERM;
 

kernel/power/hibernate.c:92

bool hibernation_available(void)
 
	return nohibernate == 0 &&
		!security_locked_down(LOCKDOWN_HIBERNATION) &&
		!secretmem_active() && !cxl_mem_active();
 

nohibernate is controlled by the kernel command line, it s set via either nohibernate or hibernate=no. security_locked_down is a hook for Linux Security Modules to prevent hibernation. This is used to prevent hibernating to an unencrypted storage device, as specified in the manual page kernel_lockdown(7). Interestingly, either level of lockdown, integrity or confidentiality, locks down hibernation because with the ability to hibernate you can extract bascially anything from memory and even reboot into a modified kernel image. secretmem_active checks whether there is any active use of memfd_secret, and if so it prevents hibernation. memfd_secret returns a file descriptor that can be mapped into a process but is specifically unmapped from the kernel s memory space. Hibernating with memory that not even the kernel is supposed to access would expose that memory to whoever could access the hibernation image. This particular feature of secret memory was apparently controversial, though not as controversial as performance concerns around fragmentation when unmapping kernel memory (which did not end up being a real problem). cxl_mem_active just checks whether any CXL memory is active. A full explanation is provided in the commit introducing this check but there s also a shortened explanation from cxl_mem_probe that sets the relevant flag when initializing a CXL memory device. drivers/cxl/mem.c:186

* The kernel may be operating out of CXL memory on this device,
* there is no spec defined way to determine whether this device
* preserves contents over suspend, and there is no simple way
* to arrange for the suspend image to avoid CXL memory which
* would setup a circular dependency between PCI resume and save
* state restoration.

Check Compression The next check is for whether compression support is enabled, and if so whether the requested algorithm is enabled. kernel/power/hibernate.c:747

/*
 * Query for the compression algorithm support if compression is enabled.
 */
if (!nocompress)  
	strscpy(hib_comp_algo, hibernate_compressor, sizeof(hib_comp_algo));
	if (crypto_has_comp(hib_comp_algo, 0, 0) != 1)  
		pr_err("%s compression is not available\n", hib_comp_algo);
		return -EOPNOTSUPP;
	 
 

The nocompress flag is set via the hibernate command line parameter, setting hibernate=nocompress. If compression is enabled, then hibernate_compressor is copied to hib_comp_algo. This synchronizes the current requested compression setting (hibernate_compressor) with the current compression setting (hib_comp_algo). Both values are character arrays of size CRYPTO_MAX_ALG_NAME (128 in this kernel). kernel/power/hibernate.c:50

static char hibernate_compressor[CRYPTO_MAX_ALG_NAME] = CONFIG_HIBERNATION_DEF_COMP;
/*
 * Compression/decompression algorithm to be used while saving/loading
 * image to/from disk. This would later be used in 'kernel/power/swap.c'
 * to allocate comp streams.
 */
char hib_comp_algo[CRYPTO_MAX_ALG_NAME];

hibernate_compressor defaults to lzo if that algorithm is enabled, otherwise to lz4 if enabled⁵. It can be overwritten using the hibernate.compressor setting to either lzo or lz4. kernel/power/Kconfig:95

choice
	prompt "Default compressor"
	default HIBERNATION_COMP_LZO
	depends on HIBERNATION
config HIBERNATION_COMP_LZO
	bool "lzo"
	depends on CRYPTO_LZO
config HIBERNATION_COMP_LZ4
	bool "lz4"
	depends on CRYPTO_LZ4
endchoice
config HIBERNATION_DEF_COMP
	string
	default "lzo" if HIBERNATION_COMP_LZO
	default "lz4" if HIBERNATION_COMP_LZ4
	help
	  Default compressor to be used for hibernation.

kernel/power/hibernate.c:1425

static const char * const comp_alg_enabled[] =  
#if IS_ENABLED(CONFIG_CRYPTO_LZO)
	COMPRESSION_ALGO_LZO,
#endif
#if IS_ENABLED(CONFIG_CRYPTO_LZ4)
	COMPRESSION_ALGO_LZ4,
#endif
 ;
static int hibernate_compressor_param_set(const char *compressor,
		const struct kernel_param *kp)
 
	unsigned int sleep_flags;
	int index, ret;
	sleep_flags = lock_system_sleep();
	index = sysfs_match_string(comp_alg_enabled, compressor);
	if (index >= 0)  
		ret = param_set_copystring(comp_alg_enabled[index], kp);
		if (!ret)
			strscpy(hib_comp_algo, comp_alg_enabled[index],
				sizeof(hib_comp_algo));
	  else  
		ret = index;
	 
	unlock_system_sleep(sleep_flags);
	if (ret)
		pr_debug("Cannot set specified compressor %s\n",
			 compressor);
	return ret;
 
static const struct kernel_param_ops hibernate_compressor_param_ops =  
	.set    = hibernate_compressor_param_set,
	.get    = param_get_string,
 ;
static struct kparam_string hibernate_compressor_param_string =  
	.maxlen = sizeof(hibernate_compressor),
	.string = hibernate_compressor,
 ;

We then check whether the requested algorithm is supported via crypto_has_comp. If not, we bail out of the whole operation with EOPNOTSUPP. As part of crypto_has_comp we perform any needed initialization of the algorithm, loading kernel modules and running initialization code as needed⁶.

Grab Locks The next step is to grab the sleep and hibernation locks via lock_system_sleep and hibernate_acquire. kernel/power/hibernate.c:758

sleep_flags = lock_system_sleep();
/* The snapshot device should not be opened while we're running */
if (!hibernate_acquire())  
	error = -EBUSY;
	goto Unlock;
 

First, lock_system_sleep marks the current thread as not freezable, which will be important later⁷. It then grabs the system_transistion_mutex, which locks taking snapshots or modifying how they are taken, resuming from a hibernation image, entering any suspend state, or rebooting.

The GFP Mask The kernel also issues a warning if the gfp mask is changed via either pm_restore_gfp_mask or pm_restrict_gfp_mask without holding the system_transistion_mutex. GFP flags tell the kernel how it is permitted to handle a request for memory. include/linux/gfp_types.h:12

 * GFP flags are commonly used throughout Linux to indicate how memory
 * should be allocated.  The GFP acronym stands for get_free_pages(),
 * the underlying memory allocation function.  Not every GFP flag is
 * supported by every function which may allocate memory.

In the case of hibernation specifically we care about the IO and FS flags, which are reclaim operators, ways the system is permitted to attempt to free up memory in order to satisfy a specific request for memory. include/linux/gfp_types.h:176

 * Reclaim modifiers
 * -----------------
 * Please note that all the following flags are only applicable to sleepable
 * allocations (e.g. %GFP_NOWAIT and %GFP_ATOMIC will ignore them).
 *
 * %__GFP_IO can start physical IO.
 *
 * %__GFP_FS can call down to the low-level FS. Clearing the flag avoids the
 * allocator recursing into the filesystem which might already be holding
 * locks.

gfp_allowed_mask sets which flags are permitted to be set at the current time. As the comment below outlines, preventing these flags from being set avoids situations where the kernel needs to do I/O to allocate memory (e.g. read/writing swap⁸) but the devices it needs to read/write to/from are not currently available. kernel/power/main.c:24

/*
 * The following functions are used by the suspend/hibernate code to temporarily
 * change gfp_allowed_mask in order to avoid using I/O during memory allocations
 * while devices are suspended.  To avoid races with the suspend/hibernate code,
 * they should always be called with system_transition_mutex held
 * (gfp_allowed_mask also should only be modified with system_transition_mutex
 * held, unless the suspend/hibernate code is guaranteed not to run in parallel
 * with that modification).
 */
static gfp_t saved_gfp_mask;
void pm_restore_gfp_mask(void)
 
	WARN_ON(!mutex_is_locked(&system_transition_mutex));
	if (saved_gfp_mask)  
		gfp_allowed_mask = saved_gfp_mask;
		saved_gfp_mask = 0;
	 
 
void pm_restrict_gfp_mask(void)
 
	WARN_ON(!mutex_is_locked(&system_transition_mutex));
	WARN_ON(saved_gfp_mask);
	saved_gfp_mask = gfp_allowed_mask;
	gfp_allowed_mask &= ~(__GFP_IO   __GFP_FS);
 

Sleep Flags After grabbing the system_transition_mutex the kernel then returns and captures the previous state of the threads flags in sleep_flags. This is used later to remove PF_NOFREEZE if it wasn t previously set on the current thread. kernel/power/main.c:52

unsigned int lock_system_sleep(void)
 
	unsigned int flags = current->flags;
	current->flags  = PF_NOFREEZE;
	mutex_lock(&system_transition_mutex);
	return flags;
 
EXPORT_SYMBOL_GPL(lock_system_sleep);

include/linux/sched.h:1633

#define PF_NOFREEZE		0x00008000	/* This thread should not be frozen */

Then we grab the hibernate-specific semaphore to ensure no one can open a snapshot or resume from it while we perform hibernation. Additionally this lock is used to prevent hibernate_quiet_exec, which is used by the nvdimm driver to active its firmware with all processes and devices frozen, ensuring it is the only thing running at that time⁹. kernel/power/hibernate.c:82

bool hibernate_acquire(void)
 
	return atomic_add_unless(&hibernate_atomic, -1, 0);
 

Prepare Console The kernel next calls pm_prepare_console. This function only does anything if CONFIG_VT_CONSOLE_SLEEP has been set. This prepares the virtual terminal for a suspend state, switching away to a console used only for the suspend state if needed. kernel/power/console.c:130

void pm_prepare_console(void)
 
	if (!pm_vt_switch())
		return;
	orig_fgconsole = vt_move_to_console(SUSPEND_CONSOLE, 1);
	if (orig_fgconsole < 0)
		return;
	orig_kmsg = vt_kmsg_redirect(SUSPEND_CONSOLE);
	return;
 

The first thing is to check whether we actually need to switch the VT kernel/power/console.c:94

/*
 * There are three cases when a VT switch on suspend/resume are required:
 *   1) no driver has indicated a requirement one way or another, so preserve
 *      the old behavior
 *   2) console suspend is disabled, we want to see debug messages across
 *      suspend/resume
 *   3) any registered driver indicates it needs a VT switch
 *
 * If none of these conditions is present, meaning we have at least one driver
 * that doesn't need the switch, and none that do, we can avoid it to make
 * resume look a little prettier (and suspend too, but that's usually hidden,
 * e.g. when closing the lid on a laptop).
 */
static bool pm_vt_switch(void)
 
	struct pm_vt_switch *entry;
	bool ret = true;
	mutex_lock(&vt_switch_mutex);
	if (list_empty(&pm_vt_switch_list))
		goto out;
	if (!console_suspend_enabled)
		goto out;
	list_for_each_entry(entry, &pm_vt_switch_list, head)  
		if (entry->required)
			goto out;
	 
	ret = false;
out:
	mutex_unlock(&vt_switch_mutex);
	return ret;
 

There is an explanation of the conditions under which a switch is performed in the comment above the function, but we ll also walk through the steps here. Firstly we grab the vt_switch_mutex to ensure nothing will modify the list while we re looking at it. We then examine the pm_vt_switch_list. This list is used to indicate the drivers that require a switch during suspend. They register this requirement, or the lack thereof, via pm_vt_switch_required. kernel/power/console.c:31

/**
 * pm_vt_switch_required - indicate VT switch at suspend requirements
 * @dev: device
 * @required: if true, caller needs VT switch at suspend/resume time
 *
 * The different console drivers may or may not require VT switches across
 * suspend/resume, depending on how they handle restoring video state and
 * what may be running.
 *
 * Drivers can indicate support for switchless suspend/resume, which can
 * save time and flicker, by using this routine and passing 'false' as
 * the argument.  If any loaded driver needs VT switching, or the
 * no_console_suspend argument has been passed on the command line, VT
 * switches will occur.
 */
void pm_vt_switch_required(struct device *dev, bool required)

Next, we check console_suspend_enabled. This is set to false by the kernel parameter no_console_suspend, but defaults to true. Finally, if there are any entries in the pm_vt_switch_list, then we check to see if any of them require a VT switch. Only if none of these conditions apply, then we return false. If a VT switch is in fact required, then we move first the currently active virtual terminal/console¹⁰ (vt_move_to_console) and then the current location of kernel messages (vt_kmsg_redirect) to the SUSPEND_CONSOLE. The SUSPEND_CONSOLE is the last entry in the list of possible consoles, and appears to just be a black hole to throw away messages. kernel/power/console.c:16

#define SUSPEND_CONSOLE	(MAX_NR_CONSOLES-1)

Interestingly, these are separate functions because you can use TIOCL_SETKMSGREDIRECT (an ioctl¹¹) to send kernel messages to a specific virtual terminal, but by default its the same as the currently active console. The locations of the previously active console and the previous kernel messages location are stored in orig_fgconsole and orig_kmsg, to restore the state of the console and kernel messages after the machine wakes up again. Interestingly, this means orig_fgconsole also ends up storing any errors, so has to be checked to ensure it s not less than zero before we try to do anything with the kernel messages on both suspend and resume. drivers/tty/vt/vt_ioctl.c:1268

/* Perform a kernel triggered VT switch for suspend/resume */
static int disable_vt_switch;
int vt_move_to_console(unsigned int vt, int alloc)
 
	int prev;
	console_lock();
	/* Graphics mode - up to X */
	if (disable_vt_switch)  
		console_unlock();
		return 0;
	 
	prev = fg_console;
	if (alloc && vc_allocate(vt))  
		/* we can't have a free VC for now. Too bad,
		 * we don't want to mess the screen for now. */
		console_unlock();
		return -ENOSPC;
	 
	if (set_console(vt))  
		/*
		 * We're unable to switch to the SUSPEND_CONSOLE.
		 * Let the calling function know so it can decide
		 * what to do.
		 */
		console_unlock();
		return -EIO;
	 
	console_unlock();
	if (vt_waitactive(vt + 1))  
		pr_debug("Suspend: Can't switch VCs.");
		return -EINTR;
	 
	return prev;
 

Unlike most other locking functions we ve seen so far, console_lock needs to be careful to ensure nothing else is panicking and needs to dump to the console before grabbing the semaphore for the console and setting a couple flags.

Panics Panics are tracked via an atomic integer set to the id of the processor currently panicking. kernel/printk/printk.c:2649

/**
 * console_lock - block the console subsystem from printing
 *
 * Acquires a lock which guarantees that no consoles will
 * be in or enter their write() callback.
 *
 * Can sleep, returns nothing.
 */
void console_lock(void)
 
	might_sleep();
	/* On panic, the console_lock must be left to the panic cpu. */
	while (other_cpu_in_panic())
		msleep(1000);
	down_console_sem();
	console_locked = 1;
	console_may_schedule = 1;
 
EXPORT_SYMBOL(console_lock);

kernel/printk/printk.c:362

/*
 * Return true if a panic is in progress on a remote CPU.
 *
 * On true, the local CPU should immediately release any printing resources
 * that may be needed by the panic CPU.
 */
bool other_cpu_in_panic(void)
 
	return (panic_in_progress() && !this_cpu_in_panic());
 

kernel/printk/printk.c:345

static bool panic_in_progress(void)
 
	return unlikely(atomic_read(&panic_cpu) != PANIC_CPU_INVALID);
 

kernel/printk/printk.c:350

/* Return true if a panic is in progress on the current CPU. */
bool this_cpu_in_panic(void)
 
	/*
	 * We can use raw_smp_processor_id() here because it is impossible for
	 * the task to be migrated to the panic_cpu, or away from it. If
	 * panic_cpu has already been set, and we're not currently executing on
	 * that CPU, then we never will be.
	 */
	return unlikely(atomic_read(&panic_cpu) == raw_smp_processor_id());
 

console_locked is a debug value, used to indicate that the lock should be held, and our first indication that this whole virtual terminal system is more complex than might initially be expected. kernel/printk/printk.c:373

/*
 * This is used for debugging the mess that is the VT code by
 * keeping track if we have the console semaphore held. It's
 * definitely not the perfect debug tool (we don't know if _WE_
 * hold it and are racing, but it helps tracking those weird code
 * paths in the console code where we end up in places I want
 * locked without the console semaphore held).
 */
static int console_locked;

console_may_schedule is used to see if we are permitted to sleep and schedule other work while we hold this lock. As we ll see later, the virtual terminal subsystem is not re-entrant, so there s all sorts of hacks in here to ensure we don t leave important code sections that can t be safely resumed.

Disable VT Switch As the comment below lays out, when another program is handling graphical display anyway, there s no need to do any of this, so the kernel provides a switch to turn the whole thing off. Interestingly, this appears to only be used by three drivers, so the specific hardware support required must not be particularly common.

drivers/gpu/drm/omapdrm/dss
drivers/video/fbdev/geode
drivers/video/fbdev/omap2

drivers/tty/vt/vt_ioctl.c:1308

/*
 * Normally during a suspend, we allocate a new console and switch to it.
 * When we resume, we switch back to the original console.  This switch
 * can be slow, so on systems where the framebuffer can handle restoration
 * of video registers anyways, there's little point in doing the console
 * switch.  This function allows you to disable it by passing it '0'.
 */
void pm_set_vt_switch(int do_switch)
 
	console_lock();
	disable_vt_switch = !do_switch;
	console_unlock();
 
EXPORT_SYMBOL(pm_set_vt_switch);

The rest of the vt_switch_console function is pretty normal, however, simply allocating space if needed to create the requested virtual terminal and then setting the current virtual terminal via set_console.

Virtual Terminal Set Console With set_console, we begin (as if we haven t been already) to enter the madness that is the virtual terminal subsystem. As mentioned previously, modifications to its state must be made very carefully, as other stuff happening at the same time could create complete messes. All this to say, calling set_console does not actually perform any work to change the state of the current console. Instead it indicates what changes it wants and then schedules that work. drivers/tty/vt/vt.c:3153

int set_console(int nr)
 
	struct vc_data *vc = vc_cons[fg_console].d;
	if (!vc_cons_allocated(nr)   vt_dont_switch  
		(vc->vt_mode.mode == VT_AUTO && vc->vc_mode == KD_GRAPHICS))  
		/*
		 * Console switch will fail in console_callback() or
		 * change_console() so there is no point scheduling
		 * the callback
		 *
		 * Existing set_console() users don't check the return
		 * value so this shouldn't break anything
		 */
		return -EINVAL;
	 
	want_console = nr;
	schedule_console_callback();
	return 0;
 

The check for vc->vc_mode == KD_GRAPHICS is where most end-user graphical desktops will bail out of this change, as they re in graphics mode and don t need to switch away to the suspend console. vt_dont_switch is a flag used by the ioctls¹¹ VT_LOCKSWITCH and VT_UNLOCKSWITCH to prevent the system from switching virtual terminal devices when the user has explicitly locked it. VT_AUTO is a flag indicating that automatic virtual terminal switching is enabled¹², and thus deliberate switching to a suspend terminal is not required. However, if you do run your machine from a virtual terminal, then we indicate to the system that we want to change to the requested virtual terminal via the want_console variable and schedule a callback via schedule_console_callback. drivers/tty/vt/vt.c:315

void schedule_console_callback(void)
 
	schedule_work(&console_work);
 

console_work is a workqueue² that will execute the given task asynchronously.

Console Callback drivers/tty/vt/vt.c:3109

/*
 * This is the console switching callback.
 *
 * Doing console switching in a process context allows
 * us to do the switches asynchronously (needed when we want
 * to switch due to a keyboard interrupt).  Synchronization
 * with other console code and prevention of re-entrancy is
 * ensured with console_lock.
 */
static void console_callback(struct work_struct *ignored)
 
	console_lock();
	if (want_console >= 0)  
		if (want_console != fg_console &&
		    vc_cons_allocated(want_console))  
			hide_cursor(vc_cons[fg_console].d);
			change_console(vc_cons[want_console].d);
			/* we only changed when the console had already
			   been allocated - a new console is not created
			   in an interrupt routine */
		 
		want_console = -1;
	 
...

console_callback first looks to see if there is a console change wanted via want_console and then changes to it if it s not the current console and has been allocated already. We do first remove any cursor state with hide_cursor. drivers/tty/vt/vt.c:841

static void hide_cursor(struct vc_data *vc)
 
	if (vc_is_sel(vc))
		clear_selection();
	vc->vc_sw->con_cursor(vc, false);
	hide_softcursor(vc);
 

A full dive into the tty driver is a task for another time, but this should give a general sense of how this system interacts with hibernation.

Notify Power Management Call Chain kernel/power/hibernate.c:767

pm_notifier_call_chain_robust(PM_HIBERNATION_PREPARE, PM_POST_HIBERNATION)

This will call a chain of power management callbacks, passing first PM_HIBERNATION_PREPARE and then PM_POST_HIBERNATION on startup or on error with another callback. kernel/power/main.c:98

int pm_notifier_call_chain_robust(unsigned long val_up, unsigned long val_down)
 
	int ret;
	ret = blocking_notifier_call_chain_robust(&pm_chain_head, val_up, val_down, NULL);
	return notifier_to_errno(ret);
 

The power management notifier is a blocking notifier chain, which means it has the following properties. include/linux/notifier.h:23

 *	Blocking notifier chains: Chain callbacks run in process context.
 *		Callouts are allowed to block.

The callback chain is a linked list with each entry containing a priority and a function to call. The function technically takes in a data value, but it is always NULL for the power management chain. include/linux/notifier.h:49

struct notifier_block;
typedef	int (*notifier_fn_t)(struct notifier_block *nb,
			unsigned long action, void *data);
struct notifier_block  
	notifier_fn_t notifier_call;
	struct notifier_block __rcu *next;
	int priority;
 ;

The head of the linked list is protected by a read-write semaphore. include/linux/notifier.h:65

struct blocking_notifier_head  
	struct rw_semaphore rwsem;
	struct notifier_block __rcu *head;
 ;

Because it is prioritized, appending to the list requires walking it until an item with lower¹³ priority is found to insert the current item before. kernel/notifier.c:252

/*
 *	Blocking notifier chain routines.  All access to the chain is
 *	synchronized by an rwsem.
 */
static int __blocking_notifier_chain_register(struct blocking_notifier_head *nh,
					      struct notifier_block *n,
					      bool unique_priority)
 
	int ret;
	/*
	 * This code gets used during boot-up, when task switching is
	 * not yet working and interrupts must remain disabled.  At
	 * such times we must not call down_write().
	 */
	if (unlikely(system_state == SYSTEM_BOOTING))
		return notifier_chain_register(&nh->head, n, unique_priority);
	down_write(&nh->rwsem);
	ret = notifier_chain_register(&nh->head, n, unique_priority);
	up_write(&nh->rwsem);
	return ret;
 

kernel/notifier.c:20

/*
 *	Notifier chain core routines.  The exported routines below
 *	are layered on top of these, with appropriate locking added.
 */
static int notifier_chain_register(struct notifier_block **nl,
				   struct notifier_block *n,
				   bool unique_priority)
 
	while ((*nl) != NULL)  
		if (unlikely((*nl) == n))  
			WARN(1, "notifier callback %ps already registered",
			     n->notifier_call);
			return -EEXIST;
		 
		if (n->priority > (*nl)->priority)
			break;
		if (n->priority == (*nl)->priority && unique_priority)
			return -EBUSY;
		nl = &((*nl)->next);
	 
	n->next = *nl;
	rcu_assign_pointer(*nl, n);
	trace_notifier_register((void *)n->notifier_call);
	return 0;
 

Each callback can return one of a series of options. include/linux/notifier.h:18

#define NOTIFY_DONE		0x0000		/* Don't care */
#define NOTIFY_OK		0x0001		/* Suits me */
#define NOTIFY_STOP_MASK	0x8000		/* Don't call further */
#define NOTIFY_BAD		(NOTIFY_STOP_MASK 0x0002)
						/* Bad/Veto action */

When notifying the chain, if a function returns STOP or BAD then the previous parts of the chain are called again with PM_POST_HIBERNATION¹⁴ and an error is returned. kernel/notifier.c:107

/**
 * notifier_call_chain_robust - Inform the registered notifiers about an event
 *                              and rollback on error.
 * @nl:		Pointer to head of the blocking notifier chain
 * @val_up:	Value passed unmodified to the notifier function
 * @val_down:	Value passed unmodified to the notifier function when recovering
 *              from an error on @val_up
 * @v:		Pointer passed unmodified to the notifier function
 *
 * NOTE:	It is important the @nl chain doesn't change between the two
 *		invocations of notifier_call_chain() such that we visit the
 *		exact same notifier callbacks; this rules out any RCU usage.
 *
 * Return:	the return value of the @val_up call.
 */
static int notifier_call_chain_robust(struct notifier_block **nl,
				     unsigned long val_up, unsigned long val_down,
				     void *v)
 
	int ret, nr = 0;
	ret = notifier_call_chain(nl, val_up, v, -1, &nr);
	if (ret & NOTIFY_STOP_MASK)
		notifier_call_chain(nl, val_down, v, nr-1, NULL);
	return ret;
 

Each of these callbacks tends to be quite driver-specific, so we ll cease discussion of this here.

Sync Filesystems The next step is to ensure all filesystems have been synchronized to disk. This is performed via a simple helper function that times how long the full synchronize operation, ksys_sync takes. kernel/power/main.c:69

void ksys_sync_helper(void)
 
	ktime_t start;
	long elapsed_msecs;
	start = ktime_get();
	ksys_sync();
	elapsed_msecs = ktime_to_ms(ktime_sub(ktime_get(), start));
	pr_info("Filesystems sync: %ld.%03ld seconds\n",
		elapsed_msecs / MSEC_PER_SEC, elapsed_msecs % MSEC_PER_SEC);
 
EXPORT_SYMBOL_GPL(ksys_sync_helper);

ksys_sync wakes and instructs a set of flusher threads to write out every filesystem, first their inodes¹⁵, then the full filesystem, and then finally all block devices, to ensure all pages are written out to disk. fs/sync.c:87

/*
 * Sync everything. We start by waking flusher threads so that most of
 * writeback runs on all devices in parallel. Then we sync all inodes reliably
 * which effectively also waits for all flusher threads to finish doing
 * writeback. At this point all data is on disk so metadata should be stable
 * and we tell filesystems to sync their metadata via ->sync_fs() calls.
 * Finally, we writeout all block devices because some filesystems (e.g. ext2)
 * just write metadata (such as inodes or bitmaps) to block device page cache
 * and do not sync it on their own in ->sync_fs().
 */
void ksys_sync(void)
 
	int nowait = 0, wait = 1;
	wakeup_flusher_threads(WB_REASON_SYNC);
	iterate_supers(sync_inodes_one_sb, NULL);
	iterate_supers(sync_fs_one_sb, &nowait);
	iterate_supers(sync_fs_one_sb, &wait);
	sync_bdevs(false);
	sync_bdevs(true);
	if (unlikely(laptop_mode))
		laptop_sync_completion();
 

It follows an interesting pattern of using iterate_supers to run both sync_inodes_one_sb and then sync_fs_one_sb on each known filesystem¹⁶. It also calls both sync_fs_one_sb and sync_bdevs twice, first without waiting for any operations to complete and then again waiting for completion¹⁷. When laptop_mode is enabled the system runs additional filesystem synchronization operations after the specified delay without any writes. mm/page-writeback.c:111

/*
 * Flag that puts the machine in "laptop mode". Doubles as a timeout in jiffies:
 * a full sync is triggered after this time elapses without any disk activity.
 */
int laptop_mode;
EXPORT_SYMBOL(laptop_mode);

However, when running a filesystem synchronization operation, the system will add an additional timer to schedule more writes after the laptop_mode delay. We don t want the state of the system to change at all while performing hibernation, so we cancel those timers. mm/page-writeback.c:2198

/*
 * We're in laptop mode and we've just synced. The sync's writes will have
 * caused another writeback to be scheduled by laptop_io_completion.
 * Nothing needs to be written back anymore, so we unschedule the writeback.
 */
void laptop_sync_completion(void)
 
	struct backing_dev_info *bdi;
	rcu_read_lock();
	list_for_each_entry_rcu(bdi, &bdi_list, bdi_list)
		del_timer(&bdi->laptop_mode_wb_timer);
	rcu_read_unlock();
 

As a side note, the ksys_sync function is simply called when the system call sync is used. fs/sync.c:111

SYSCALL_DEFINE0(sync)
 
	ksys_sync();
	return 0;
 

The End of Preparation With that the system has finished preparations for hibernation. This is a somewhat arbitrary cutoff, but next the system will begin a full freeze of userspace to then dump memory out to an image and finally to perform hibernation. All this will be covered in future articles!

1. Hibernation modes are outside of scope for this article, see the previous article for a high-level description of the different types of hibernation.
2. Workqueues are a mechanism for running asynchronous tasks. A full description of them is a task for another time, but the kernel documentation on them is available here: https://www.kernel.org/doc/html/v6.9/core-api/workqueue.html ²
3. This is a bit of an oversimplification, but since this isn t the main focus of this article this description has been kept to a higher level.
4. Kconfig is Linux s build configuration system that sets many different macros to enable/disable various features.
5. Kconfig defaults to the first default found
6. Including checking whether the algorithm is larval? Which appears to indicate that it requires additional setup, but is an interesting choice of name for such a state.
7. Specifically when we get to process freezing, which we ll get to in the next article in this series.
8. Swap space is outside the scope of this article, but in short it is a buffer on disk that the kernel uses to store memory not current in use to free up space for other things. See Swap Management for more details.
9. The code for this is lengthy and tangential, thus it has not been included here. If you re curious about the details of this, see kernel/power/hibernate.c:858 for the details of hibernate_quiet_exec, and drivers/nvdimm/core.c:451 for how it is used in nvdimm.
10. Annoyingly this code appears to use the terms console and virtual terminal interchangeably.
11. ioctls are special device-specific I/O operations that permit performing actions outside of the standard file interactions of read/write/seek/etc. ²
12. I m not entirely clear on how this flag works, this subsystem is particularly complex.
13. In this case a higher number is higher priority.
14. Or whatever the caller passes as val_down, but in this case we re specifically looking at how this is used in hibernation.
15. An inode refers to a particular file or directory within the filesystem. See Wikipedia for more details.
16. Each active filesystem is registed with the kernel through a structure known as a superblock, which contains references to all the inodes contained within the filesystem, as well as function pointers to perform the various required operations, like sync.
17. I m including minimal code in this section, as I m not looking to deep dive into the filesystem code at this time.

1. LWN: The history, status, and plans for reproducible builds
2. Intermediate Autotools build artifacts removed from PostgreSQL distribution tarballs
3. Distribution news
4. Mailing list news
5. diffoscope
6. Website updates
7. Upstream patches
8. Reproducibility testing framework

LWN: The history, status, and plans for reproducible builds The free software newspaper of record, Linux Weekly News, published an in-depth article based on Holger Levsen s talk, Reproducible Builds: The First Eleven Years which was presented at the recent DebConf24 conference in Busan, South Korea. Titled The history, status, and plans for reproducible builds and written by Jake Edge, LWN s article not only summarises Holger s talk and clarifies its message but it links to external information as well. Holger s original talk can also be watched on the DebConf24 webpage (direct .webm link and his HTML slides are available also). There are also a significant number of comments on LWN s page as well. Holger Levsen also headed a scheduled discussion session at DebConf24 on Preserving *other* build artifacts addressing a topic where a number of Debian packages are (or would like to) produce results that are neither the .deb files, the build logs nor the logs of CI tests. This is an issue for reproducible builds as this 4th type of build artifact are typically shipped within the binary .deb packages, and are invariably non-deterministic; thus making the .deb files unreproducible. (A direct .webm link and HTML slides are available).

Intermediate Autotools build artifacts removed from PostgreSQL distribution tarballs Peter Eisentraut wrote a detailed blog post on the subject of The new PostgreSQL 17 make dist . Like many projects, the PostgreSQL database has previously pre-built parts of its GNU Autotools build system: the reason for this is a mix of convenience and traditional practice . Peter astutely notes that this arrangement in the build system is quite tricky as:

You need to carefully maintain the different states of clean source code , partially built source code , and fully built source code , and the commands to transition between them.

However, Peter goes on to mention that:

a lot more attention is nowadays paid to the software supply chain. There are security and legal reasons for this. When users install software, they want to know where it came from, and they want to be sure that they got the right thing, not some fake version or some version of dubious legal provenance.

And cites the XZ Utils backdoor as a reason to care about transparent and reproducible ways of distributing and communicating a source tarball and provenance. Because of this, intermediate build artifacts are now henceforth essentially disallowed from PostgreSQL distribution tarballs.

Distribution news In Debian this month, 30 reviews of Debian packages were added, 17 were updated and 10 were removed this month adding to our knowledge about identified issues. One issue type was added by Chris Lamb, too. [ ] In addition, an issue was filed to update the Salsa CI pipeline (used by 1,000s of Debian packages) to no longer test for reproducibility with reprotest s build_path variation. Holger Levsen provided a rationale for this change in the issue, which has already been made to the tests being performed by tests.reproducible-builds.org.
In Arch Linux this month, Jelle van der Waa published a short blog post on the topic of Investigating creating reproducible images with mkosi, motivated by the desire to make it possible for anyone to re-recreate the official Arch cloud image bit-by-bit identical on their own machine as per [the] reproducible builds definition. In addition, Jelle filed a patch for pacman, the Arch Linux package manager, to respect the SOURCE_DATE_EPOCH environment variable when installing a package.
In openSUSE news, Bernhard M. Wiedemann published another report for that distribution.
In Android news, the IzzyOnDroid project added 49 new rebuilder recipes and now features 256 total reproducible applications representing 21% of the total offerings in the repository. IzzyOnDroid is an F-Droid style repository for Android apps[:] applications in this repository are official binaries built by the original application developers, taken from their resp. repositories (mostly GitHub).

Mailing list news From our mailing list this month:

• Bernhard M. Wiedemann posted a brief message to the list with some helpful information regarding nondeterminism within Rust binaries, positing the use of the codegen-units = 16 default and resulting in a bug being filed in the Rust issue tracker. [ ]
• Bernhard also wrote to the list, following up to a thread in November 2023, on attempts to make the LibreOffice suite of office applications build reproducibly. In the thread from this month, Bernhard could announce that the four patches previously mentioned have landed in LibreOffice upstream.
• Fay Stegerman linked the mailing list to a thread she made on the Signal issue tracker regarding whether device-specific binaries [can] ever be considered meaningfully reproducible . In particular: the whole part about allow[ing] multiple third parties to come to a consensus on a correct result breaks down completely when correct is device-specific and not something everyone can agree on. [ ]
• Developer kpcyrd posted an update for source code indexing project, whatsrc.org. Announcing that it now importing packages from live-bootstrap ( a usable Linux system [that is] created with only human-auditable, and wherever possible, human-written, source code ) into its database of provenance data.
• Lastly, Mechtilde Stehmann posted an update to an earlier thread about how Java builds are not reproducible on the armhf architecture, enquiring how they might gain temporary access to such a machine in order to perform some deeper testing. [ ]

diffoscope diffoscope is our in-depth and content-aware diff utility that can locate and diagnose reproducibility issues. This month, Chris Lamb released versions 274, 275, 276 and 277, uploaded these to Debian, and made the following changes as well:

• New features:
  • Strip ANSI escapes usually colour codes from the output of the Procyon Java decompiler. [ ]
  • Factor out a method for stripping ANSI escapes. [ ]
  • Append output from dumppdf(1) in more cases, avoiding situations where we fallback to a binary diff. [ ]
  • Add support for versions of Perl s IO::Compress::Zip version 2.212. [ ]
• Bug fixes:
  • Also catch RuntimeError exceptions when importing the PyPDF library so that it, or, crucially, its transitive dependencies, cannot not cause diffoscope to traceback at runtime and build time. [ ]
  • Do not call marshal.load( ) of precompiled Python bytecode as it, alas, inherently unsafe. Replace for now with a brief summary of the code section of .pyc. [ ][ ]
  • Don t include excessive debug output when calling dumppdf(1). [ ]
• Testsuite-related changes:
  • Don t bother to check version number in test_python.py: the fixture for this test is fixed. [ ][ ]
  • Update test_zip text fixtures and definitions to support new changes to the Perl IO::Compress library. [ ]

In addition, Mattia Rizzolo updated the available architectures for a number of test dependencies [ ] and Sergei Trofimovich fixed an issue to avoid diffoscope crashing when hashing directory symlinks [ ] and Vagrant Cascadian proposed GNU Guix updates for diffoscope versions [275 and 276 and [277.

Website updates There were a rather substantial number of improvements made to our website this month, including:

• Alba Herrerias:
  • Substantially extend the guidance on the Contribute page. [ ]
• Chris Lamb:
  • Set the future: true configuration value so we render all files and documents in the website, regardless of whether they have a date property in the future. After all, we don t re-generate the website on a timer, and have other ways of making unpublished, draft posts. [ ][ ]
• Fay Stegerman:
  • Add IzzyOnDroid (IoD) to the Projects page. [ ]
• hulkoba:
  • Considerably overhaul the History page in the documentation, linking strip-nondeterminism and SOURCE_DATE_EPOCH [ ], fixing the test statistics link [ ], adjusting the Google Summer of Code application link [ ], a link to a Debian bug [ ], and removed a dead link to the debhelper utility [ ].
  • Use the jekyll-sitemap plugin to create a sitemap for the website. [ ]
  • Use raw HTML to avoid a literal .lead directive appearing in the page. [ ]
  • Fix a number of issues on the Virtual machine drivers page, such as keeping the Gitian info, linking (and then removing) an issue on the Bitcoin issue tracker [ ] and fixing a link to the Bazel website [ ].
  • Address a broken footnote link on the Timestamps page. [ ]
  • Unify the style on the Commandments of Reproducible Builds page in order to match other documentation entries. [ ]
  • Add a table of contents to the main Documentation page. [ ]
  • Avoid a number of so-called here links on the Variations in the build environment page. [ ]
  • Fix a link to the man2html patch on the SOURCE_DATE_EPOCH documentation page. [ ]
  • Fix a link to sources.debian.org on the Randomness page. [ ]
• kpcyrd:
  • Fix a typo on the Variations in the build environment page. [ ]
• Mattia Rizzolo:
  • Add all the sponsors to the Hamburg 2024 summit page. [ ][ ][ ][ ][ ]
  • Fix a link in the summit sponsor prospectus PDF. [ ]
• Pol Dellaiera:
  • Fix the DoI for their thesis on the Publications page. [ ]

Upstream patches The Reproducible Builds project detects, dissects and attempts to fix as many currently-unreproducible packages as possible. We endeavour to send all of our patches upstream where appropriate. This month, we wrote a large number of such patches, including:

• Bernhard M. Wiedemann:
  • agama-integration-tests (uses a random TCP-port number in .lock file)
  • ca-certificates-mozilla:ca-certificates-mozilla-prebuilt
  • cosmic (hash order issue)
  • openSUSE (meta-issue to test reproducibility in the openSUSE Build Service)
  • pop-launcher (parallelism-related issue)
  • post (toolchain-issue, avoiding Rust parallelism)
  • rpm-config-SUSE (date-related issue)
  • rust (Rust toolchain issue)
  • weblate (build gets stuck)
• Chris Lamb:
  • #1078048 filed against scikit-optimize.
  • #1078153 filed against pan.
  • #1078687 filed against tetzle.
  • #1079041 filed against apg.
  • #1079312 filed against receptor.
• James Addison:
  • #1064782 forwarded and merged in bind9-doc
  • #1066083 forwarded and merged in gnome-maps

Reproducibility testing framework The Reproducible Builds project operates a comprehensive testing framework running primarily at tests.reproducible-builds.org in order to check packages and other artifacts for reproducibility. In August, a number of changes were made by Holger Levsen, including:

• Temporarily install the openssl-provider-legacy package for the Debian unstable environments for running diffoscope due to Debian bug #1078944. [ ][ ][ ][ ]
• Mark Debian armhf architecture nodes as being down due to proxy down. [ ][ ]
• Detect proxy failures. [ ][ ][ ]
• Run the index-buildinfo for the builtin-pho script with the -q switch. [ ]
• Disable all Arch Linux reproducible jobs. [ ]

In addition, Mattia Rizzolo updated the website configuration to install the ruby-jekyll-sitemap package as it is now used in the website [ ], Roland Clobus updated the script to build Debian live images to treat openQA issues as warnings [ ], and Vagrant Cascadian marked the cbxi4b node as down [ ].

---

If you are interested in contributing to the Reproducible Builds project, please visit our Contribute page on our website. However, you can get in touch with us via:

• IRC: #reproducible-builds on irc.oftc.net.
• Mastodon: @reproducible_builds@fosstodon.org
• Mailing list: rb-general@lists.reproducible-builds.org
• Twitter: @ReproBuilds

"Well," said Tiffany, "there's too much to be done and not enough people to do it." The smile that the kelda gave her was a strange one. The little woman said, "Do ye let them try? Ye mustn't be afraid to ask for help. Pride is a good thing, my girl, but it will kill you in time."

"Granny never said as she was better than others. She just got on with it and showed 'em and people worked it out for themselves."

Rust First I want to talk about Rust, which is the language I chose to use for the problems. I ve dabbled a little in it, but I d like more familiarity with the basic language, and some programming problems seemed like a good way to get that. It s a language I want to like; I ve spent a lot of my career writing C, do more in Go these days, and generally think Rust promises a low level, run-time light environment like C but with the rough edges taken off. I set myself the challenge of using just bare Rust; no external crates, no use of cargo. I was accused of playing on hard mode by doing this, but it really wasn t the intention - I figured that I should be able to do what I needed without recourse to anything outside the core language, and didn t want what seemed like the extra complexity of dealing with cargo. That caused problems, however. I m used to by-default generic error handling in Go through the error type, but Rust seems to have much more tightly typed errors. I was pointed at anyhow as the right way to do this in Rust. I still find this surprising; I ended up using unwrap() a lot when I think with more generic error handling I could have used ?. The other thing I discovered is that by default rustc is heavy on the debug output. I got significantly better results on some of the solutions with rustc -O -C target-cpu=native source.rs. I probably shouldn t be surprised by this, but worth noting. Rust, to me, has a syntax only a C++ programmer could love. I am not a C++ programmer. Coming from C I found Go to be a nice, simple syntax to learn. Rust has not been the same. There s a lot more punctuation, and it s not always clear to me what it s doing. This applies more when reading other people s code than when writing it myself, obviously, but I see a lot of Rust code that could give Perl a run for its money in terms of looking like line noise. The borrow checker didn t bug me too much, but did add overhead to my thinking. The Rust compiler is generally very good at outputting helpful error messages when the programmer is an idiot. I ended up having to use a RefCell for one solution, and using .iter() for loops rather than explicit iterators (why, why is this different?). I also kept forgetting to explicitly mark variables as mutable when declaring them. Things I liked? There s a rich set of first class data types. Look, I m a C programmer, I m easily pleased. You give me some sort of hash array and I ll be happy. Rust manages that, tuples, strings, all the standard bits any modern language can provide. The whole impl thing for adding methods to structures I like as a way of providing some abstraction, though I think Go has a nicer syntax for it. The compiler, as mentioned, is great at spitting out useful errors for the most part. Also although I wasn t using external crates for AoC I do appreciate there s a decent ecosystem there now (though that brings up another gripe: rust seems to still be a fairly fast moving target, to the extent I can no longer rely on the compiler in Debian stable to be able to compile random projects I find).

Advent of Code Let s talk about the advent of code bit now. Hopefully it s long enough since it came out that this won t be spoilers for anyone, but if you haven t attempted the 2023 AoC and might, you might want to stop reading here. First, a refresher on the format for those who might not be aware of it. Problems are posted daily from December 1st until the 25th. Each is in 2 parts; the second part is not viewable until you have provided the correct answer for the first part. There s a whole leaderboard thing going on, but the puzzle opens at midnight UTC-5 so generally by the time I wake up and have time to look the problem has been solved many times over; no chance of getting listed. Credit to AoC creator, Eric Wastl, for writing up the set of problems in an entertaining fashion. I quite enjoyed seeing how the puzzle would be phrased each day, and the whole thing obviously brings a lot of joy to folk I know. I always start AoC thinking it ll be a fun set of puzzles to solve. Then something happens and I miss a day or two, and all of a sudden I ve a bunch of catching up to do and it s all a bit more of a chore. I hit that at some points this time, but made a concerted effort to try and power through it. That perseverance was required up front, because I found the second part of Day 1 to be ill specified, and had to iterate a few times to actually calculate the desired solution (IIRC, issues about whether sevenone at the end of a line ended up as 7 or 1 really tripped me up). I don t recall any other problems that bit me as hard on the specification as this one, but it happening up front was unfortunate. The short example input doesn t always help with this either; either it s not enough to be able to extrapolate patterns, or it doesn t show all the variations you need to account for (that aren t fully specified in the text), or in a few cases it turned out I needed to understand the shape of the actual data to produce a solution that could actually complete in a reasonable time. Which brings me to another matter, sometimes brute force doesn t actually work. This is fine, but the second part of the day s problem can change the approach you d take. So sometimes I got lucky in the way I handled the first half, and doing the second half was a simple 5 minute tweak, and sometimes I had to entirely change the way I was storing data. You might claim that if I was a better programmer I d have always produced a first half solution that was amenable to extension for the second half. First, I dispute that; I think there are always situations where the problem domain can change in enough directions that you can t handle all of them without a lot of effort. Secondly, I didn t find AoC an environment that encouraged me to optimise for generic solutions. Maybe some of the puzzles in isolation would allow for that, but a month of daily problems to solve while still engaging in regular life meant I hacked things up, took short cuts based on the knowledge I had of the input data, etc, etc. Overall I can see the appeal, but the sheer quantity and the fact I write code as part of my day job just made it feel too much like a chore, rather than a fun mental exercise. I did wonder how they d look as a set of interview puzzles (obviously a subset, rather than all of them), but I m not sure how you d actually use them for that - I wouldn t want anyone to have to solve them in a live interview. So, in case it s not obvious, I m not planning to engage in AoC again this yet. But I m continuing to persevere with Rust (though most of my work stuff is thankfully still Go).

• Michelle Nery (IFSULDEMINAS) e Andr Martins (UNIV S) pelo aux lio na organiza o local
• Paulo Santana (Debian Brasil) pela organiza o geral
• Virg nia Cardoso, Giovani Ferreira, Marco Ant nio e Thiago Pezzo pelas palestras
• E um agradecimento especial a todas e todos que participaram da nossa comemora o!

• VFS appointment letter
• Duly-filled visa application form
• Original passport
• Copy of passport
• 1 photograph
• My 6 months bank account statement
• Cover letter
• Consent form (that visa processing will take up to 15 business days)
• Snehal s job contract
• My work contract
• Rent contract of Snehal
• Residence permit of Snehal
• A copy of Snehal s passport
• Invitation letter from Snehal
• Return flight ticket reservations
• Travel insurance for the intended travel dates

Subject: AUSTRIAN VISA APPLICATION - AMENDMENT REQUEST: Ravi Dwivedi VIS 4331 Dear Applicant, On 22.12.2023 your application for Visa C was registered at the Embassy. You are requested to kindly send the scanned copies of the following documents via email to the Embassy or submit the documents at the nearest VFS centre, for further processing of your application:

• Kindly submit Electronic letter of guarantee EVE- Elektronische Verpflichtungserkl rung obtained from the Fremdenpolizeibeh rde of the sponsor s district in Austria. Once your host company/inviting company has obtained the EVE, please share the reference number (starting from DEL_____) received from the authorities, with the Embassy.

Kindly Note: It is in your own interest to fulfil the requirements as indicated above and submit the missing documents within 14 days of the receipt of this email. Otherwise a decision will be taken based on the documentation available. Sie werden in Ihrem Interesse ersucht, die gekennzeichneten M ngel so schnell wie m glich zu beheben bzw. fehlende Unterlagen umgehend nachzureichen, um die weitere Bearbeitung des Antrages zu erm glichen. Sollten Sie innerhalb 14 Tagen die gekennzeichneten M ngel nicht beheben bzw. die fehlenden Unterlagen nicht nachreichen, wird ber den vorliegenden Antrag ohne diese Unterlagen bzw. M ngelbehebung entschieden. Austrian Embassy New Delhi R.J/ Consular Section +91 11 2419 2700 EP-13, Chandragupta Marg, Chanakyapuri, New Delhi 110 021, India bmeia.gv.at/botschaft/new-delhi facebook.at/AustrianEmbassyNewDelhihttp://www.facebook.at/AustrianEmbassyNewDelhi twitter.com/MFA_Austriahttp://www.twitter.com/MFA_Austria [refocus1][Signatur_V+30]https://www.bmeia.gv.at/en/european-foreign-policy/foreign-trade/refocus-austria/[Logo_AT_IN_22px]

The Austrian embassy in Delhi examined your application; the visa has been refused. The decision is based on the following reason(s):

• The information submitted regarding the justification for the purpose and conditions of the intended stay was not reliable.
• There are reasonable doubts as to your intention to leave the territory of the Member States before the expiry of the visa.

Other remarks: You have been given an amendment request, which you have failed to fulfil, or have only fulfilled inadequately, within the deadline set. You are a first-time traveller. The social and economic roots with the home country are not evident. The return from Schengen territory does therefore not seem to be certain.

The social and economic roots with the home country are not evident.

1. If you are visiting a host, then the category of appointment at VFS must be Visiting Friends and Family rather than Tourist .
2. VFS charged me for courier assurance, which is an optional service. Make sure to get these removed from your bill.
3. Neither my travel agent nor the VFS application center mentioned the EVE.
4. While the required documents list from the VFS website does mention it in point 6, it leads to a dead link.
5. Snehal informed me that a mere two months ago, his wife s visa was approved without an EVE. This hints at inconsistency in processing of applications, even those under identical categories.

1. Reproducible Builds Summit 2024
2. Pulling Linux up by its bootstraps
3. Towards Idempotent Rebuilds?
4. AROMA: Automatic Reproduction of Maven Artifacts
5. Community updates
6. Android Reproducible Builds at IzzyOnDroid with rbtlog
7. Extending the Scalability, Flexibility and Responsiveness of Secure Software Update Systems
8. Development news
9. Website updates
10. Upstream patches
11. Reproducibility testing framework

Reproducible Builds Summit 2024 Last month, we were very pleased to announce the upcoming Reproducible Builds Summit, set to take place from September 17th 19th 2024 in Hamburg, Germany. We are thrilled to host the seventh edition of this exciting event, following the success of previous summits in various iconic locations around the world, including Venice, Marrakesh, Paris, Berlin and Athens. Our summits are a unique gathering that brings together attendees from diverse projects, united by a shared vision of advancing the Reproducible Builds effort. During this enriching event, participants will have the opportunity to engage in discussions, establish connections and exchange ideas to drive progress in this vital field. Our aim is to create an inclusive space that fosters collaboration, innovation and problem-solving. If you re interesting in joining us this year, please make sure to read the event page, which has more details about the event and location. We are very much looking forward to seeing many readers of these reports there.

Pulling Linux up by its bootstraps (LWN) In a recent edition of Linux Weekly News, Daroc Alden has written an article on bootstrappable builds. Starting with a brief introduction that

a bootstrappable build is one that builds existing software from scratch for example, building GCC without relying on an existing copy of GCC. In 2023, the Guix project announced that the project had reduced the size of the binary bootstrap seed needed to build its operating system to just 357-bytes not counting the Linux kernel required to run the build process.

The article goes onto to describe that now, the live-bootstrap project has gone a step further and removed the need for an existing kernel at all. and concludes:

The real benefit of bootstrappable builds comes from a few things. Like reproducible builds, they can make users more confident that the binary packages downloaded from a package mirror really do correspond to the open-source project whose source code they can inspect. Bootstrappable builds have also had positive effects on the complexity of building a Linux distribution from scratch [ ]. But most of all, bootstrappable builds are a boon to the longevity of our software ecosystem. It s easy for old software to become unbuildable. By having a well-known, self-contained chain of software that can build itself from a small seed, in a variety of environments, bootstrappable builds can help ensure that today s software is not lost, no matter where the open-source community goes from here

Towards Idempotent Rebuilds? Trisquel developer Simon Josefsson wrote an interesting blog post comparing the output of the .deb files from our tests.reproducible-builds.org testing framework and the ones in the official Debian archive. Following up from a previous post on the reproducibility of Trisquel, Simon notes that typically [the] rebuilds do not match the official packages, even when they say the package is reproducible , Simon correctly identifies that the purpose of [these] rebuilds are not to say anything about the official binary build, instead the purpose is to offer a QA service to maintainers by performing two builds of a package and declaring success if both builds match. However, Simon s post swiftly moves on to announce a new tool called debdistrebuild that performs rebuilds of the difference between two distributions in a GitLab pipeline and displays diffoscope output for further analysis.

AROMA: Automatic Reproduction of Maven Artifacts Mehdi Keshani, Tudor-Gabriel Velican, Gideon Bot and Sebastian Proksch of the Delft University of Technology, Netherlands, have published a new paper in the ACM Software Engineering on a new tool to automatically reproduce Apache Maven artifacts:

Reproducible Central is an initiative that curates a list of reproducible Maven libraries, but the list is limited and challenging to maintain due to manual efforts. [We] investigate the feasibility of automatically finding the source code of a library from its Maven release and recovering information about the original release environment. Our tool, AROMA, can obtain this critical information from the artifact and the source repository through several heuristics and we use the results for reproduction attempts of Maven packages. Overall, our approach achieves an accuracy of up to 99.5% when compared field-by-field to the existing manual approach [and] we reveal that automatic reproducibility is feasible for 23.4% of the Maven packages using AROMA, and 8% of these packages are fully reproducible.

Community updates On our mailing list this month:

• Nichita Morcotilo reached out to the community, first to share their efforts to build reproducible packages cross-platform with a new build tool called rattler-build, noting that as you can imagine, building packages reproducibly on Windows is the hardest challenge (so far!) . Nichita goes onto mention that the Apple ecosystem appears to be using ZERO_AR_DATE over SOURCE_DATE_EPOCH. [ ]
• Roland Clobus announced that the Debian bookworm 12.6 live images are nearly reproducible , with more detail in the post itself and input in the thread from other contributors.
• As reported in last month s report, Pol Dellaiera completed his master thesis on Reproducibility in Software Engineering at the University of Mons, Belgium. This month, Pol announced this on the list with more background info. Since the master thesis sources have been available, it has received some feedback and contributions. As a result, an updated version of the thesis has been published containing those community fixes.
• Daniel Gr ber asked for help in getting the Yosys documentation to build reproducibly, citing issues in inter alia the PDF generation causing differing CreationDate metadata values.
• James Addison continued his long journey towards getting the Sphinx documentation generator to build reproducible documentation. In this thread, James concerns himself with the problem that even when SOURCE_DATE_EPOCH is configured, Sphinx projects that have configured their copyright notices using dynamic elements can produce nonsensical output under some circumstances. James query ended up generating a number of replies.
• Allen gunner Gunner posted a brief update on the progress the core team is making towards introducing a Code of Conduct (CoC) such that it is in place in time for the RB Summit in Hamburg in September . In particular, gunner asks if you are interested in helping with CoC design and development in the weeks ahead, simply email rb-core@lists.reproducible-builds.org and let us know . [ ]

Android Reproducible Builds at IzzyOnDroid with rbtlog On our mailing list, Fay Stegerman announced a new Reproducible Builds collaboration in the Android ecosystem:

We are pleased to announce Reproducible Builds, special client support and more in our repo : a collaboration between various independent interoperable projects: the IzzyOnDroid team, 3rd-party clients Droid-ify & Neo Store, and rbtlog (part of my collection of tools for Android Reproducible Builds) to bring Reproducible Builds to IzzyOnDroid and the wider Android ecosystem.

Extending the Scalability, Flexibility and Responsiveness of Secure Software Update Systems Congratulations to Marina Moore of the New York Tandon School of Engineering who has submitted her PhD thesis on Extending the Scalability, Flexibility and Responsiveness of Secure Software Update Systems. The introduction outlines its contributions to the field:

[S]oftware repositories are a vital component of software development and release, with packages downloaded both for direct use and to use as dependencies for other software. Further, when software is updated due to patched vulnerabilities or new features, it is vital that users are able to see and install this patched version of the software. However, this process of updating software can also be the source of attack. To address these attacks, secure software update systems have been proposed. However, these secure software update systems have seen barriers to widespread adoption. The Update Framework (TUF) was introduced in 2010 to address several attacks on software update systems including repository compromise, rollback attacks, and arbitrary software installation. Despite this, compromises continue to occur, with millions of users impacted by such compromises. My work has addressed substantial challenges to adoption of secure software update systems grounded in an understanding of practical concerns. Work with industry and academic communities provided opportunities to discover challenges, expand adoption, and raise awareness about secure software updates. [ ]

Development news In Debian this month, 12 reviews of Debian packages were added, 13 were updated and 6 were removed this month adding to our knowledge about identified issues. A new toolchain issue type was identified as well, specifically ordering_differences_in_pkg_info.
Colin Percival filed a bug against the LLVM compiler noting that building i386 binaries on the i386 architecture is different when building i386 binaries under amd64. The fix was narrowed down to x87 excess precision, which can result in slightly different register choices when the compiler is hosted on x86_64 or i386 and a fix committed. [ ]
Fay Stegerman performed some in-depth research surrounding her apksigcopier tool, after some Android .apk files signed with the latest apksigner could no longer be verified as reproducible. Fay identified the issue as follows:

Since build-tools >= 35.0.0-rc1, backwards-incompatible changes to apksigner break apksigcopier as it now by default forcibly replaces existing alignment padding and changed the default page alignment from 4k to 16k (same as Android Gradle Plugin >= 8.3, so the latter is only an issue when using older AGP). [ ]

She documented multiple available workarounds and filed a bug in Google s issue tracker.
Lastly, diffoscope is our in-depth and content-aware diff utility that can locate and diagnose reproducibility issues. This month, Chris Lamb uploaded version 272 and Mattia Rizzolo uploaded version 273 to Debian, and the following changes were made as well:

• Chris Lamb:
  • Ensure that the convert utility is from ImageMagick version 6.x. The command-line interface has seemingly changed with the 7.x series of ImageMagick. [ ]
  • Factor out version detection in test_jpeg_image. [ ]
  • Correct the import of the identify_version method after a refactoring change in a previous commit. [ ]
  • Move away from using DSA OpenSSH keys in tests as support has been deprecated and removed in OpenSSH version 9.8p1. [ ]
  • Move to assert_diff in the test_openssh_pub_key package. [ ]
  • Update copyright years. [ ]
• Mattia Rizzolo:
  • Add support for ffmpeg version 7.x which adds some extra context to the diff. [ ]
  • Rework the handling of OpenSSH testing of DSA keys if OpenSSH is strictly 9.7, and add an OpenSSH key test with a ed25519-format key [ ][ ][ ]
  • Temporarily disable a few packages that are not available in Debian testing. [ ][ ]
  • Stop ignoring the results of Debian testing in the continuous integration system. [ ]
  • Adjust options in debian/source to make sure not to pack the Python sdist directory into the binary Debian package. [ ]
  • Adjust Lintian overrides. [ ]

Website updates There were a number of improvements made to our website this month, including:

• Bernhard M. Wiedemann updated the SOURCE_DATE_EPOCH page to include instructions on how to create reproducible .zip files from within Python using the zipfile module. [ ]
• Chris Lamb fixed a potential duplicate heading on the Projects page. [ ]
• Fay Stegerman added rbtlog to the Tools page [ ] and IzzyOnDroid to the Projects page [ ], also ensuring that the latter page was always sorted regardless of the ordering within the input data files. [ ]
• Holger Levsen added Linus Nordberg to our global list of contributors [ ] as well as made a number of changes to the page for the upcoming Reproducible Builds summit later this year [ ][ ][ ][ ].
• Mattia Rizzolo updated the Civil Infrastructure Platform logo [ ] and also updated the 2024 summit page [ ][ ].
• Nichita Morcotilo added rattler-build to the Projects page. [ ][ ][ ]
• Pol Dellaiera updated the Academic Publications page, adding two publications. [ ][ ]

Upstream patches The Reproducible Builds project detects, dissects and attempts to fix as many currently-unreproducible packages as possible. We endeavour to send all of our patches upstream where appropriate. This month, we wrote a large number of such patches, including:

• Bernhard M. Wiedemann:
  • armagetron (date)
  • blaspp (hostname)
  • cligen (GnuTLSs date)
  • cloudflared (date)
  • dpdk (Sphinx doctrees)
  • fonttosfnt/xorg-x11-fonts (toolchain, date)
  • gegl (build machine details)
  • gettext-runtime (jar mtime)
  • kf6-kirigami+kf6-qqc2-desktop-style (race-condition)
  • kubernetes1.26 (backport upstream fix for random path)
  • lapackpp (hostname)
  • latex2html (nochecks)
  • libdb-4_8 (.jar modification time)
  • librcc (already merged upstream)
  • libreoffice (strip .jar mtimes + clucene-core toolchain)
  • maliit-keyboard (nocheck)
  • nautilus (date)
  • openblas (CPU type, fixed)
  • openssl-3 (random-related issue)
  • python-ruff (ASLR)
  • python3 (date, parallelism/race)
  • reproducible-faketools (0.5.2)
  • sphinx (GZip modification time)
  • sphinxcontrib (gzip mtime)
• Chris Lamb:
  • #1076368 filed against nautilus.
  • #1076507 filed against mccode.
  • #1076806 filed against meson-python.
  • #1077479 filed against debcraft.
  • #1077485 filed against pytest.
  • #1077601 filed against setuptools.
• Fridrich Strba:
  • javapackages-tools
  • ant
  • java-21-openjdk
• Evangelos Ribeiro Tzaras:
  • buffybox

Reproducibility testing framework The Reproducible Builds project operates a comprehensive testing framework running primarily at tests.reproducible-builds.org in order to check packages and other artifacts for reproducibility. In July, a number of changes were made by Holger Levsen, including:

• Grant bremner access to the ionos7 node. [ ][ ]
• Perform a dummy change to force update of all jobs. [ ][ ]

In addition, Vagrant Cascadian performed some necessary node maintenance of the underlying build hosts. [ ]

---

If you are interested in contributing to the Reproducible Builds project, please visit our Contribute page on our website. However, you can get in touch with us via:

• IRC: #reproducible-builds on irc.oftc.net.
• Mastodon: @reproducible_builds@fosstodon.org
• Mailing list: rb-general@lists.reproducible-builds.org
• Twitter: @ReproBuilds

• [1] https://tinyurl.com/ytwvpary
• [2] https://www.davidbrin.com/nonfiction/immortality.html
• [3] https://tinyurl.com/26czjpjl
• [4] https://sams-blog.com/?p=5615
• [5] https://worksinprogress.co/issue/the-maintenance-race/
• [6] https://www.youtube.com/watch?v=NhajAqI66nU
• [7] https://hashman.ca/me-cfs/
• [8] https://tinyurl.com/29b4h5oz
• [9] https://tinyurl.com/24sz7lwa
• [10] https://tinyurl.com/2c6dx8d4
• [11] https://tinyurl.com/26e3xxmn
• [12] https://tinyurl.com/26ykzgn4
• [13] https://www.youtube.com/watch?v=5V6Pez_Dbzs
• [14] https://tinyurl.com/27h5urv9

1. Introduction
2. Initial evaluation and adaptation
3. Issues extending Polis and adjusting our goals (this article)
4. Creating (a) new frontend(s) for Polis
5. Current status and roadmap

1. metadata questions,
2. seed statements,
3. and participant statements

1. Small, Christopher T., Bjorkegren, Michael, Erkkil , Timo, Shaw, Lynette and Megill, Colin (2021). Polis: Scaling deliberation by mapping high dimensional opinion spaces. Recerca. Revista de Pensament i An lisi, 26(2), pp. 1-26.

project('example', 'cpp', version: '1.0', license : ' ', default_options: ['warning_level=everything', 'cpp_std=c++17'])
subdir('example')

test_example = executable('example-test', ['main.cc'])

/* This file intentionally left empty */

#include <cstring>
int main(int argc,const char* argv[])
 
    std::string foo("foo");
    return 0;
 

$ meson setup builddir
The Meson build system
Version: 1.0.1
Source dir: /home/enrico/dev/deb/wobble-repr
Build dir: /home/enrico/dev/deb/wobble-repr/builddir
Build type: native build
Project name: example
Project version: 1.0
C++ compiler for the host machine: ccache c++ (gcc 12.2.0 "c++ (Debian 12.2.0-14) 12.2.0")
C++ linker for the host machine: c++ ld.bfd 2.40
Host machine cpu family: x86_64
Host machine cpu: x86_64
Build targets in project: 1
Found ninja-1.11.1 at /usr/bin/ninja
$ ninja -C builddir
ninja: Entering directory  builddir'
[1/2] Compiling C++ object example/example-test.p/main.cc.o
FAILED: example/example-test.p/main.cc.o
ccache c++ -Iexample/example-test.p -Iexample -I../example -fdiagnostics-color=always -D_FILE_OFFSET_BITS=64 -Wall -Winvalid-pch -Wextra -Wpedantic -Wcast-qual -Wconversion -Wfloat-equal -Wformat=2 -Winline -Wmissing-declarations -Wredundant-decls -Wshadow -Wundef -Wuninitialized -Wwrite-strings -Wdisabled-optimization -Wpacked -Wpadded -Wmultichar -Wswitch-default -Wswitch-enum -Wunused-macros -Wmissing-include-dirs -Wunsafe-loop-optimizations -Wstack-protector -Wstrict-overflow=5 -Warray-bounds=2 -Wlogical-op -Wstrict-aliasing=3 -Wvla -Wdouble-promotion -Wsuggest-attribute=const -Wsuggest-attribute=noreturn -Wsuggest-attribute=pure -Wtrampolines -Wvector-operation-performance -Wsuggest-attribute=format -Wdate-time -Wformat-signedness -Wnormalized=nfc -Wduplicated-cond -Wnull-dereference -Wshift-negative-value -Wshift-overflow=2 -Wunused-const-variable=2 -Walloca -Walloc-zero -Wformat-overflow=2 -Wformat-truncation=2 -Wstringop-overflow=3 -Wduplicated-branches -Wattribute-alias=2 -Wcast-align=strict -Wsuggest-attribute=cold -Wsuggest-attribute=malloc -Wanalyzer-too-complex -Warith-conversion -Wbidi-chars=ucn -Wopenacc-parallelism -Wtrivial-auto-var-init -Wctor-dtor-privacy -Weffc++ -Wnon-virtual-dtor -Wold-style-cast -Woverloaded-virtual -Wsign-promo -Wstrict-null-sentinel -Wnoexcept -Wzero-as-null-pointer-constant -Wabi-tag -Wuseless-cast -Wconditionally-supported -Wsuggest-final-methods -Wsuggest-final-types -Wsuggest-override -Wmultiple-inheritance -Wplacement-new=2 -Wvirtual-inheritance -Waligned-new=all -Wnoexcept-type -Wregister -Wcatch-value=3 -Wextra-semi -Wdeprecated-copy-dtor -Wredundant-move -Wcomma-subscript -Wmismatched-tags -Wredundant-tags -Wvolatile -Wdeprecated-enum-enum-conversion -Wdeprecated-enum-float-conversion -Winvalid-imported-macros -std=c++17 -O0 -g -MD -MQ example/example-test.p/main.cc.o -MF example/example-test.p/main.cc.o.d -o example/example-test.p/main.cc.o -c ../example/main.cc
In file included from ../example/main.cc:1:
/usr/include/c++/12/cstring:77:11: error:  memchr  has not been declared in  :: 
   77     using ::memchr;
                  ^~~~~~
/usr/include/c++/12/cstring:78:11: error:  memcmp  has not been declared in  :: 
   78     using ::memcmp;
                  ^~~~~~
/usr/include/c++/12/cstring:79:11: error:  memcpy  has not been declared in  :: 
   79     using ::memcpy;
                  ^~~~~~
/usr/include/c++/12/cstring:80:11: error:  memmove  has not been declared in  :: 
   80     using ::memmove;
                  ^~~~~~~
 

Another thing to note is that include_directories adds both the source directory and corresponding build directory to include path, so you don't have to care.

1. Next Reproducible Builds Summit dates announced
2. GNU Guix patch review session for reproducibility
3. New reproducibility-related academic papers
4. Misc development news
5. Website updates
6. Reproducibility testing framework

Next Reproducible Builds Summit dates announced We are very pleased to announce the upcoming Reproducible Builds Summit, set to take place from September 17th 19th 2024 in Hamburg, Germany. We are thrilled to host the seventh edition of this exciting event, following the success of previous summits in various iconic locations around the world, including Venice, Marrakesh, Paris, Berlin and Athens. Our summits are a unique gathering that brings together attendees from diverse projects, united by a shared vision of advancing the Reproducible Builds effort. During this enriching event, participants will have the opportunity to engage in discussions, establish connections and exchange ideas to drive progress in this vital field. Our aim is to create an inclusive space that fosters collaboration, innovation and problem-solving. If you re interesting in joining us this year, please make sure to read the event page which has more details about the event and location. We are very much looking forward to seeing many readers of these reports there.

GNU Guix patch review session for reproducibility Vagrant Cascadian will be holding a Reproducible Builds session as part of the monthly Guix patch review series on July 11th at 17:00 UTC. These online events are intended to encourage everyone everyone becoming a patch reviewer and the goal of reviewing patches is to help Guix project accept contributions while maintaining our quality standards and learning how to do patch reviews together in a friendly hacking session.

New reproducibility-related academic papers Multiple scholarly papers related to Reproducible Builds were published this month: An Industry Interview Study of Software Signing for Supply Chain Security was published by Kelechi G. Kalu, Tanmay Singla, Chinenye Okafor, Santiago Torres-Arias and James C. Davis of Electrical and Computer Engineering department of Purdue University, Indiana, USA, and is concerned with:

To understand software signing in practice, we interviewed 18 high-ranking industry practitioners across 13 organizations. We provide possible impacts of experienced software supply chain failures, security standards, and regulations on software signing adoption. We also study the challenges that affect an effective software signing implementation.

DiVerify: Diversifying Identity Verification in Next-Generation Software Signing was written by Chinenye L. Okafor, James C. Davis and Santiago Torres-Arias also of Purdue University and is interested in:

Code signing enables software developers to digitally sign their code using cryptographic keys, thereby associating the code to their identity. This allows users to verify the authenticity and integrity of the software, ensuring it has not been tampered with. Next-generation software signing such as Sigstore and OpenPubKey simplify code signing by providing streamlined mechanisms to verify and link signer identities to the public key. However, their designs have vulnerabilities: reliance on an identity provider introduces a single point of failure, and the failure to follow the principle of least privilege on the client side increases security risks. We introduce Diverse Identity Verification (DiVerify) scheme, which strengthens the security guarantees of next-generation software signing by leveraging threshold identity validations and scope mechanisms.

Felix Lagn hed published their thesis on the Integration of Reproducibility Verification with Diffoscope in GNU Make. This work, amongst some other results:

[ ] resulted in an extension of GNU make which is called rmake, where diffoscope a tool for detecting differences between a large number of file types was integrated into the workflow of make. rmake was later used to answer the posed research questions for this thesis. We found that different build paths and offsets are a big problem as three out of three tested Free and Open Source Software projects all contained these variations. The results also showed that gcc s optimisation levels did not affect reproducibility, but link-time optimisation embeds a lot of unreproducible information in build artefacts. Lastly, the results showed that build paths, build ID s and randomness are the three most common groups of variations encountered in the wild and potential solutions for some variations were proposed.

Lastly, Pol Dellaiera completed his master thesis on Reproducibility in Software Engineering at the University of Mons, Belgium, under the supervision of Dr. Tom Mens, professor and director of the Software Engineering Lab.

The thesis serves as an introduction to the concept of reproducibility in software engineering, offering a comprehensive overview of formalizations using mathematical notations for key concepts and an empirical evaluation of several key tools. By exploring various case studies, methodologies and tools, the research aims to provide actionable insights for practitioners and researchers alike.

Development news In Debian this month, 4 reviews of Debian packages were added, 11 were updated and 14 were removed this month adding to our knowledge about identified issues. Only one issue types was updated, though, explaining that we don t vary the build path anymore.
On our mailing list this month, Bernhard M. Wiedemann wrote that whilst he had previously collected issues that introduce non-determinism he has now moved on to discuss about mitigations , in the sense of how can we avoid whole categories of problem without patching an infinite number of individual packages . In addition, Janneke Nieuwenhuizen announced the release of two versions of GNU Mes. [ ][ ]
In openSUSE news, Bernhard M. Wiedemann published another report for that distribution.
In NixOS, with the 24.05 release out, it was again validated that our minimal ISO is reproducible by building it on a virtual machine with no access to the binary cache.
What s more, we continued to write patches in order to fix specific reproducibility issues, including Bernhard M. Wiedemann writing three patches (for qutebrowser, samba and systemd), Chris Lamb filing Debian bug #1074214 against the fastfetch package and Arnout Engelen proposing fixes to refind and for the Scala compiler [ .
Lastly, diffoscope is our in-depth and content-aware diff utility that can locate and diagnose reproducibility issues. This month, Chris Lamb uploaded two versions (270 and 271) to Debian, and made the following changes as well:

• Drop Build-Depends on liblz4-tool in order to fix Debian bug #1072575. [ ]
• Update tests to support zipdetails version 4.004 that is shipped with Perl 5.40. [ ]

Website updates There were a number of improvements made to our website this month, including Akihiro Suda very helpfully making the <h4> elements more distinguishable from the <h3> level [ ][ ] as well as adding a guide for Dockerfile reproducibility [ ]. In addition Fay Stegerman added two tools, apksigcopier and reproducible-apk-tools, to our Tools page.

Reproducibility testing framework The Reproducible Builds project operates a comprehensive testing framework running primarily at tests.reproducible-builds.org in order to check packages and other artifacts for reproducibility. In June, a number of changes were made by Holger Levsen, including:

• Marking the virt(32 64)c-armhf nodes as down. [ ]
• Granting a developer access to the osuosl4 node in order to debug a regression on the ppc64el architecture. [ ]
• Granting a developer access to the osuosl4 node. [ ][ ]

In addition, Mattia Rizzolo re-aligned the /etc/default/jenkins file with changes performed upstream [ ] and changed how configuration files are handled on the rb-mail1 host. [ ], whilst Vagrant Cascadian documented the failure of the virt32c and virt64c nodes after initial investigation [ ].

---

If you are interested in contributing to the Reproducible Builds project, please visit our Contribute page on our website. However, you can get in touch with us via:

• IRC: #reproducible-builds on irc.oftc.net.
• Mastodon: @reproducible_builds@fosstodon.org
• Mailing list: rb-general@lists.reproducible-builds.org
• Twitter: @ReproBuilds

#  image   x y z temperature
image1.png 1 2 5 34
image2.png 3 4 1 35

dtype = np.dtype([ ('image',       'U16'),
                   ('x y z',       int, (3,)),
                   ('temperature', float), ])
arr = vnlog.slurp("data.vnl", dtype=dtype)

print(arr['image'])
---> array(['image1.png', 'image2.png'], dtype='<U16')
print(arr['x y z'])
---> array([[1, 2, 5],
            [3, 4, 1]])
print(arr['temperature'])
---> array([34., 35.])

• The given structured dtype defines both how to organize the data, and which data to extract. So it can be used to read in only a subset of the available columns. Here I could have omitted the temperature column, for instance
• Sub-arrays are allowed. In the example I could say either

  dtype = np.dtype([ ('image',       'U16'),
                     ('x y z',       int, (3,)),
                     ('temperature', float), ])
  

  or

  dtype = np.dtype([ ('image',       'U16'),
                     ('x',           int),
                     ('y',           int),
                     ('z',           int),
                     ('temperature', float), ])
  

  The latter would read x, y, z into separate, individual arrays. Sometime we want this, sometimes not.
• Nested structured dtypes are not allowed. Fields inside other fields are not supported, since it's not clear how to map that to a flat vnlog legend
• If a structured dtype is given, slurp() returns the array only, since the field names are already available in the dtype

"I'm a witch. It's what we do. When it's nobody else's business, it's my business."

I should have learned this, she thought. I wanted to learn fire, and pain, but I should have learned people.

"There have been times, lately, when I dearly wished that I could change the past. Well, I can't, but I can change the present, so that when it becomes the past it will turn out to be a past worth having."

• [1] https://tinyurl.com/23e9vd7b
• [2] https://en.wikipedia.org/wiki/Homeschooling