fs/binfmt_elf.c: 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

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>

diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index ecd8d26..7bb0deb 100644 (file)
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -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;
 }