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| author | H.J. Lu <hjl.tools@gmail.com> | 2017-10-30 10:02:16 -0700 |
|---|---|---|
| committer | H.J. Lu <hjl.tools@gmail.com> | 2017-10-30 10:02:30 -0700 |
| commit | c5cc45148c89cc5c57d1946348dd242d4db5c5f5 (patch) | |
| tree | ceee1e4fcc30daa0d3716353d5ffd6ac587508e1 /ChangeLog | |
| parent | ce12269fac8cb873df1a8785e4a6cde870855590 (diff) | |
| download | glibc-c5cc45148c89cc5c57d1946348dd242d4db5c5f5.tar.gz glibc-c5cc45148c89cc5c57d1946348dd242d4db5c5f5.tar.xz glibc-c5cc45148c89cc5c57d1946348dd242d4db5c5f5.zip | |
i586: Use conditional branches in strcpy.S [BZ #22353]
i586 strcpy.S used a clever trick with LEA to implement jump table:
/* ECX has the last 2 bits of the address of source - 1. */
andl $3, %ecx
call 2f
2: popl %edx
/* 0xb is the distance between 2: and 1:. */
leal 0xb(%edx,%ecx,8), %ecx
jmp *%ecx
.align 8
1: /* ECX == 0 */
orb (%esi), %al
jz L(end)
stosb
xorl %eax, %eax
incl %esi
/* ECX == 1 */
orb (%esi), %al
jz L(end)
stosb
xorl %eax, %eax
incl %esi
/* ECX == 2 */
orb (%esi), %al
jz L(end)
stosb
xorl %eax, %eax
incl %esi
/* ECX == 3 */
L(1): movl (%esi), %ecx
leal 4(%esi),%esi
This fails if there are instruction length changes before L(1):. This
patch replaces it with conditional branches:
cmpb $2, %cl
je L(Src2)
ja L(Src3)
cmpb $1, %cl
je L(Src1)
L(Src0):
which have similar performance and work with any instruction lengths.
Tested on i586 and i686 with and without --disable-multi-arch.
[BZ #22353]
* sysdeps/i386/i586/strcpy.S (STRCPY): Use conditional branches.
(1): Renamed to ...
(L(Src0)): This.
(L(Src1)): New.
(L(Src2)): Likewise.
(L(1)): Renamed to ...
(L(Src3)): This.
Diffstat (limited to 'ChangeLog')
| -rw-r--r-- | ChangeLog | 11 |
1 files changed, 11 insertions, 0 deletions
diff --git a/ChangeLog b/ChangeLog index 59612389c9..5ea3d856a1 100644 --- a/ChangeLog +++ b/ChangeLog @@ -1,3 +1,14 @@ +2017-10-30 H.J. Lu <hongjiu.lu@intel.com> + + [BZ #22353] + * sysdeps/i386/i586/strcpy.S (STRCPY): Use conditional branches. + (1): Renamed to ... + (L(Src0)): This. + (L(Src1)): New. + (L(Src2)): Likewise. + (L(1)): Renamed to ... + (L(Src3)): This. + 2017-10-30 Joseph Myers <joseph@codesourcery.com> * math/math.h [__HAVE_FLOAT16 && __USE_GNU] (M_Ef16): New macro. |