https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71585
Bug ID: 71585
Summary: Cannot selectively disable stack protector with LTO
Product: gcc
Version: 5.3.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: js at alien8 dot de
Target Milestone: ---
The following code includes a function that is intended to not be compiled with
a stack canary. This is a reduced example from an embedded project, where this
function is the function that actually sets the __stack_chk_guard variable.
The code is this:
#pragma GCC push_options
#pragma GCC optimize ("-fno-stack-protector")
__attribute__((constructor)) void foo()
{
asm ("");
}
#pragma GCC pop_options
int main() { return 0; }
When compiled without LTO ( gcc -fstack-protector-all -O2 -o main
lto-func-attr.c ), it correctly emits a non-stack-protected function foo():
00000000004004c0 <foo>:
4004c0: c3 ret
When compiled with LTO ( gcc -fstack-protector-all -flto -O2 -o main
lto-func-attr.c ), it incorrectly emits a stack canary check:
00000000004004a0 <foo>:
4004a0: 48 83 ec 18 sub rsp,0x18
4004a4: 64 48 8b 04 25 28 00 mov rax,QWORD PTR fs:0x28
4004ab: 00 00
4004ad: 48 89 44 24 08 mov QWORD PTR [rsp+0x8],rax
4004b2: 31 c0 xor eax,eax
4004b4: 48 8b 44 24 08 mov rax,QWORD PTR [rsp+0x8]
4004b9: 64 48 33 04 25 28 00 xor rax,QWORD PTR fs:0x28
4004c0: 00 00
4004c2: 75 05 jne 4004c9 <foo+0x29>
4004c4: 48 83 c4 18 add rsp,0x18
4004c8: c3 ret
4004c9: e8 72 ff ff ff call 400440 <__stack_chk_fail@plt>
The expected behavior is that even with LTO, no stack canary check is emitted.
I am using gcc (GCC) 5.3.1 20160406 (Red Hat 5.3.1-6) running on Fedora 23
x86_64.
