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patch from njk: make x86_64 __uniclone branchless.
author
Rich Felker
<dalias@aerifal.cx>
Wed, 16 Feb 2011 14:49:54 +0000
(09:49 -0500)
committer
Rich Felker
<dalias@aerifal.cx>
Wed, 16 Feb 2011 14:49:54 +0000
(09:49 -0500)
src/thread/x86_64/clone.s
patch
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diff --git
a/src/thread/x86_64/clone.s
b/src/thread/x86_64/clone.s
index
5141005
..
3cefd93
100644
(file)
--- a/
src/thread/x86_64/clone.s
+++ b/
src/thread/x86_64/clone.s
@@
-4,6
+4,7
@@
.type __uniclone,%function
/* rdi = child_stack, rsi = start, rdx = pthread_struct */
__uniclone:
.type __uniclone,%function
/* rdi = child_stack, rsi = start, rdx = pthread_struct */
__uniclone:
+ subq $8,%rsp /* pad parent stack to prevent branch later */
subq $16,%rdi /* grow child_stack */
mov %rsi,8(%rdi) /* push start onto child_stack as return ptr */
mov %rdx,0(%rdi) /* push pthread_struct onto child_stack */
subq $16,%rdi /* grow child_stack */
mov %rsi,8(%rdi) /* push start onto child_stack as return ptr */
mov %rdx,0(%rdi) /* push pthread_struct onto child_stack */
@@
-13,10
+14,9
@@
__uniclone:
movl $56,%eax /* clone syscall number */
movl $0x7d0f00,%edi /* rdi = flags */
mov %r10,%rdx /* rdx = parent_id */
movl $56,%eax /* clone syscall number */
movl $0x7d0f00,%edi /* rdi = flags */
mov %r10,%rdx /* rdx = parent_id */
- syscall /* clone(flags, child_stack, parent_id,
- * child_id, tls) */
- test %rax,%rax
- jnz 1f /* if we're in the parent -> goto 1f */
- pop %rdi /* restore pthread_struct from child stack */
-1: ret
+ syscall /* clone(flags, child_stack, parent_id,
+ * child_id, tls) */
+ pop %rdi /* child stack: restore pthread_struct
+ * parent stack: undo rsp displacement */
+ ret
.size __uniclone,.-__uniclone
.size __uniclone,.-__uniclone