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authorRich Felker <dalias@aerifal.cx>2011-02-16 09:49:54 -0500
committerRich Felker <dalias@aerifal.cx>2011-02-16 09:49:54 -0500
commit22cd9cae819a0fd432da4b1d21502a242871e5d9 (patch)
tree39aaffd5e4fb3feacb755ad4d5a02c0bb096dc28 /src/thread/x86_64
parentbad481266e8744f8c4241e577f06e8cabf6f7f89 (diff)
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patch from njk: make x86_64 __uniclone branchless.
Diffstat (limited to 'src/thread/x86_64')
-rw-r--r--src/thread/x86_64/clone.s12
1 files changed, 6 insertions, 6 deletions
diff --git a/src/thread/x86_64/clone.s b/src/thread/x86_64/clone.s
index 51410051..3cefd933 100644
--- 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:
+ 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 */
@@ -13,10 +14,9 @@ __uniclone:
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