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Subject[PATCH] ELF: smaller code generation around auxv vector fill
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

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
---

fs/binfmt_elf.c | 15 ++++++++-------
1 file changed, 8 insertions(+), 7 deletions(-)

--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -177,7 +177,7 @@ create_elf_tables(struct linux_binprm *bprm, const 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;

@@ -231,8 +231,8 @@ create_elf_tables(struct linux_binprm *bprm, const 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
@@ -276,12 +276,13 @@ create_elf_tables(struct linux_binprm *bprm, const 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;
@@ -339,7 +340,7 @@ create_elf_tables(struct linux_binprm *bprm, const 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;
}
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