From 21431a0e43a65e9547c9a23497f074f861bcab8b Mon Sep 17 00:00:00 2001 From: Alexander Monakov Date: Tue, 11 Aug 2020 21:11:14 +0300 Subject: 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. --- src/setjmp/x86_64/longjmp.s | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) (limited to 'src/setjmp/x86_64/longjmp.s') 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 _longjmp: longjmp: - 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 */ 1: mov (%rdi),%rbx /* rdi is the jmp_buf, restore regs from it */ mov 8(%rdi),%rbp -- cgit v1.2.1