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Commit 27e64b4b authored by Dave Martin's avatar Dave Martin Committed by Will Deacon
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regset: Add support for dynamically sized regsets



Currently the regset API doesn't allow for the possibility that
regsets (or at least, the amount of meaningful data in a regset)
may change in size.

In particular, this results in useless padding being added to
coredumps if a regset's current size is smaller than its
theoretical maximum size.

This patch adds a get_size() function to struct user_regset.
Individual regset implementations can implement this function to
return the current size of the regset data.  A regset_size()
function is added to provide callers with an abstract interface for
determining the size of a regset without needing to know whether
the regset is dynamically sized or not.

The only affected user of this interface is the ELF coredump code:
This patch ports ELF coredump to dump regsets with their actual
size in the coredump.  This has no effect except for new regsets
that are dynamically sized and provide a get_size() implementation.

Signed-off-by: default avatarDave Martin <Dave.Martin@arm.com>
Reviewed-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Dmitry Safonov <dsafonov@virtuozzo.com>
Cc: H. J. Lu <hjl.tools@gmail.com>
Signed-off-by: default avatarWill Deacon <will.deacon@arm.com>
parent c7f5828b
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+5 −5
Original line number Diff line number Diff line
@@ -1699,7 +1699,7 @@ static int fill_thread_core_info(struct elf_thread_core_info *t,
				 long signr, size_t *total)
{
	unsigned int i;
	unsigned int regset_size = view->regsets[0].n * view->regsets[0].size;
	unsigned int regset0_size = regset_size(t->task, &view->regsets[0]);

	/*
	 * NT_PRSTATUS is the one special case, because the regset data
@@ -1708,11 +1708,11 @@ static int fill_thread_core_info(struct elf_thread_core_info *t,
	 * We assume that regset 0 is NT_PRSTATUS.
	 */
	fill_prstatus(&t->prstatus, t->task, signr);
	(void) view->regsets[0].get(t->task, &view->regsets[0], 0, regset_size,
	(void) view->regsets[0].get(t->task, &view->regsets[0], 0, regset0_size,
				    &t->prstatus.pr_reg, NULL);

	fill_note(&t->notes[0], "CORE", NT_PRSTATUS,
		  PRSTATUS_SIZE(t->prstatus, regset_size), &t->prstatus);
		  PRSTATUS_SIZE(t->prstatus, regset0_size), &t->prstatus);
	*total += notesize(&t->notes[0]);

	do_thread_regset_writeback(t->task, &view->regsets[0]);
@@ -1728,7 +1728,7 @@ static int fill_thread_core_info(struct elf_thread_core_info *t,
		if (regset->core_note_type && regset->get &&
		    (!regset->active || regset->active(t->task, regset))) {
			int ret;
			size_t size = regset->n * regset->size;
			size_t size = regset_size(t->task, regset);
			void *data = kmalloc(size, GFP_KERNEL);
			if (unlikely(!data))
				return 0;
@@ -1743,7 +1743,7 @@ static int fill_thread_core_info(struct elf_thread_core_info *t,
						  size, data);
				else {
					SET_PR_FPVALID(&t->prstatus,
							1, regset_size);
							1, regset0_size);
					fill_note(&t->notes[i], "CORE",
						  NT_PRFPREG, size, data);
				}
+60 −7
Original line number Diff line number Diff line
@@ -106,6 +106,28 @@ typedef int user_regset_writeback_fn(struct task_struct *target,
				     const struct user_regset *regset,
				     int immediate);

/**
 * user_regset_get_size_fn - type of @get_size function in &struct user_regset
 * @target:	thread being examined
 * @regset:	regset being examined
 *
 * This call is optional; usually the pointer is %NULL.
 *
 * When provided, this function must return the current size of regset
 * data, as observed by the @get function in &struct user_regset.  The
 * value returned must be a multiple of @size.  The returned size is
 * required to be valid only until the next time (if any) @regset is
 * modified for @target.
 *
 * This function is intended for dynamically sized regsets.  A regset
 * that is statically sized does not need to implement it.
 *
 * This function should not be called directly: instead, callers should
 * call regset_size() to determine the current size of a regset.
 */
typedef unsigned int user_regset_get_size_fn(struct task_struct *target,
					     const struct user_regset *regset);

/**
 * struct user_regset - accessible thread CPU state
 * @n:			Number of slots (registers).
@@ -117,19 +139,33 @@ typedef int user_regset_writeback_fn(struct task_struct *target,
 * @set:		Function to store values.
 * @active:		Function to report if regset is active, or %NULL.
 * @writeback:		Function to write data back to user memory, or %NULL.
 * @get_size:		Function to return the regset's size, or %NULL.
 *
 * This data structure describes a machine resource we call a register set.
 * This is part of the state of an individual thread, not necessarily
 * actual CPU registers per se.  A register set consists of a number of
 * similar slots, given by @n.  Each slot is @size bytes, and aligned to
 * @align bytes (which is at least @size).
 * @align bytes (which is at least @size).  For dynamically-sized
 * regsets, @n must contain the maximum possible number of slots for the
 * regset, and @get_size must point to a function that returns the
 * current regset size.
 *
 * These functions must be called only on the current thread or on a
 * thread that is in %TASK_STOPPED or %TASK_TRACED state, that we are
 * guaranteed will not be woken up and return to user mode, and that we
 * have called wait_task_inactive() on.  (The target thread always might
 * wake up for SIGKILL while these functions are working, in which case
 * that thread's user_regset state might be scrambled.)
 * Callers that need to know only the current size of the regset and do
 * not care about its internal structure should call regset_size()
 * instead of inspecting @n or calling @get_size.
 *
 * For backward compatibility, the @get and @set methods must pad to, or
 * accept, @n * @size bytes, even if the current regset size is smaller.
 * The precise semantics of these operations depend on the regset being
 * accessed.
 *
 * The functions to which &struct user_regset members point must be
 * called only on the current thread or on a thread that is in
 * %TASK_STOPPED or %TASK_TRACED state, that we are guaranteed will not
 * be woken up and return to user mode, and that we have called
 * wait_task_inactive() on.  (The target thread always might wake up for
 * SIGKILL while these functions are working, in which case that
 * thread's user_regset state might be scrambled.)
 *
 * The @pos argument must be aligned according to @align; the @count
 * argument must be a multiple of @size.  These functions are not
@@ -156,6 +192,7 @@ struct user_regset {
	user_regset_set_fn		*set;
	user_regset_active_fn		*active;
	user_regset_writeback_fn	*writeback;
	user_regset_get_size_fn		*get_size;
	unsigned int			n;
	unsigned int 			size;
	unsigned int 			align;
@@ -371,5 +408,21 @@ static inline int copy_regset_from_user(struct task_struct *target,
	return regset->set(target, regset, offset, size, NULL, data);
}

/**
 * regset_size - determine the current size of a regset
 * @target:	thread to be examined
 * @regset:	regset to be examined
 *
 * Note that the returned size is valid only until the next time
 * (if any) @regset is modified for @target.
 */
static inline unsigned int regset_size(struct task_struct *target,
				       const struct user_regset *regset)
{
	if (!regset->get_size)
		return regset->n * regset->size;
	else
		return regset->get_size(target, regset);
}

#endif	/* <linux/regset.h> */