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: Dave Martin <Dave.Martin@arm.com>
Reviewed-by: Catalin 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: Will Deacon <will.deacon@arm.com>

1 files changed, 5 insertions, 5 deletions

diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index 73b01e474fdc..c697882b3aba 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -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);
 				}