path: root/src/setjmp/x86_64/longjmp.s
diff options
authorAlexander Monakov <>2020-08-11 21:11:14 +0300
committerRich Felker <>2020-08-11 14:42:54 -0400
commit21431a0e43a65e9547c9a23497f074f861bcab8b (patch)
tree633bce5d95ccd614b93e15ab5a227a3d9f852e9d /src/setjmp/x86_64/longjmp.s
parentc2feda4e2ea61f4da73f2f38b2be5e327a7d1a91 (diff)
setjmp: fix x86-64 longjmp argument adjustment
longjmp 'val' argument is an int, but the assembly is referencing 64-bit registers as if the argument was a long, or the caller was responsible for extending the argument. Though the psABI is not clear on this, the interpretation in GCC is that high bits may be arbitrary and the callee is responsible for sign/zero-extending the value as needed (likewise for return values: callers must anticipate that high bits may be garbage). Therefore testing %rax is a functional bug: setjmp would wrongly return zero if longjmp was called with val==0, but high bits of %rsi happened to be non-zero. Rewrite the prologue to refer to 32-bit registers. In passing, change 'test' to use %rsi, as there's no advantage to using %rax and the new form is cheaper on processors that do not perform move elimination.
Diffstat (limited to 'src/setjmp/x86_64/longjmp.s')
1 files changed, 3 insertions, 3 deletions
diff --git a/src/setjmp/x86_64/longjmp.s b/src/setjmp/x86_64/longjmp.s
index e175a4b9..e709acad 100644
--- a/src/setjmp/x86_64/longjmp.s
+++ b/src/setjmp/x86_64/longjmp.s
@@ -5,10 +5,10 @@
.type longjmp,@function
- mov %rsi,%rax /* val will be longjmp return */
- test %rax,%rax
+ mov %esi,%eax /* val will be longjmp return */
+ test %esi,%esi
jnz 1f
- inc %rax /* if val==0, val=1 per longjmp semantics */
+ inc %eax /* if val==0, val=1 per longjmp semantics */
mov (%rdi),%rbx /* rdi is the jmp_buf, restore regs from it */
mov 8(%rdi),%rbp