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fs/binfmt_elf.c: smaller code generation around auxv vector fill

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Filling auxv vector as array with index (auxv[i++] = ...) generates
terrible code.  "saved_auxv" should be reworked because it is the worst
member of mm_struct by size/usefullness ratio but do it later.

Meanwhile help gcc a little with *auxv++ idiom.

Space savings on x86_64:

	add/remove: 0/0 grow/shrink: 0/1 up/down: 0/-127 (-127)
	Function                                     old     new   delta
	load_elf_binary                             5470    5343    -127

Link: http://lkml.kernel.org/r/20191208172301.GD19716@avx2
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Alexey Dobriyan 2020-01-30 22:16:50 -08:00 committed by Linus Torvalds
parent 7dfaa98f64
commit 1f83d80677
1 changed files with 8 additions and 7 deletions
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15
fs/binfmt_elf.c
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@ -176,7 +176,7 @@ create_elf_tables(struct linux_binprm *bprm, struct elfhdr *exec,
unsigned char k_rand_bytes[16];
int items;
elf_addr_t *elf_info;
int ei_index = 0;
int ei_index;
const struct cred *cred = current_cred();
struct vm_area_struct *vma;
@ -230,8 +230,8 @@ create_elf_tables(struct linux_binprm *bprm, struct elfhdr *exec,
/* update AT_VECTOR_SIZE_BASE if the number of NEW_AUX_ENT() changes */
#define NEW_AUX_ENT(id, val) \
do { \
elf_info[ei_index++] = id; \
elf_info[ei_index++] = val; \
*elf_info++ = id; \
*elf_info++ = val; \
} while (0)
#ifdef ARCH_DLINFO
@ -275,12 +275,13 @@ create_elf_tables(struct linux_binprm *bprm, struct elfhdr *exec,
}
#undef NEW_AUX_ENT
/* AT_NULL is zero; clear the rest too */
memset(&elf_info[ei_index], 0,
sizeof current->mm->saved_auxv - ei_index * sizeof elf_info[0]);
memset(elf_info, 0, (char *)current->mm->saved_auxv +
sizeof(current->mm->saved_auxv) - (char *)elf_info);
/* And advance past the AT_NULL entry. */
ei_index += 2;
elf_info += 2;
ei_index = elf_info - (elf_addr_t *)current->mm->saved_auxv;
sp = STACK_ADD(p, ei_index);
items = (argc + 1) + (envc + 1) + 1;
@ -338,7 +339,7 @@ create_elf_tables(struct linux_binprm *bprm, struct elfhdr *exec,
current->mm->env_end = p;
/* Put the elf_info on the stack in the right place. */
if (copy_to_user(sp, elf_info, ei_index * sizeof(elf_addr_t)))
if (copy_to_user(sp, current->mm->saved_auxv, ei_index * sizeof(elf_addr_t)))
return -EFAULT;
return 0;
}