| Issue |
124238
|
| Summary |
ASan breaks __seg_gs
|
| Labels |
new issue
|
| Assignees |
|
| Reporter |
glandium
|
Take this source:
```
#include <cstdint>
void test(uintptr_t addr) {
__builtin_memcpy((void __seg_gs*)addr, "x", 1);
}
```
It compiles to
```
test(unsigned long):
push rbp
mov rbp, rsp
mov qword ptr [rbp - 8], rdi
mov rax, qword ptr [rbp - 8]
mov byte ptr gs:[rax], 120
pop rbp
ret
```
Or even
```
test(unsigned long):
mov byte ptr gs:[rdi], 120
ret
```
Without ASan, but with ASan:
```
test(unsigned long):
push rbp
mov rbp, rsp
sub rsp, 16
mov qword ptr [rbp - 8], rdi
mov rdi, qword ptr [rbp - 8]
lea rsi, [rip + .str]
mov edx, 1
call __asan_memcpy@PLT
add rsp, 16
pop rbp
ret
```
The `gs:` addressing is gone.
Funnily enough, with `-O` + ASan, it compiles to the same thing as without ASan.
Obligatory godbolt link: https://godbolt.org/z/8hWGxdc3P
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