| Issue |
179581
|
| Summary |
MSan: false negative on bitfields
|
| Labels |
compiler-rt:msan,
false-negative
|
| Assignees |
|
| Reporter |
yus3710-fj
|
This looks similar to #39856, but it would not be the same.
(FYI: #39856 is not reproducible on my environment now.)
MemorySanitizer does not detect the use of an uninitialized value when `-O2` or higher is specified.
```cpp
typedef struct {unsigned char a:3; unsigned char b:6;} ss;
__attribute__((noinline))
int foo(ss* sp) {
sp->a=0b101;
return 0;
}
int main() {
ss s;
s.a = 0b101;
foo(&s);
if (s.b) return 1;
return 0;
}
```
```console
$ clang++ -O2 -fsanitize=memory -g test.cc && ./a.out
$ clang++ -O1 -fsanitize=memory -g test.cc && ./a.out
==404358==WARNING: MemorySanitizer: use-of-uninitialized-value
#0 0x55a10938daf8 in main /path/to/test.cc:14:1
#1 0x7f37cd663d8f (/lib/x86_64-linux-gnu/libc.so.6+0x29d8f) (BuildId: 4f7b0c955c3d81d7cac1501a2498b69d1d82bfe7)
#2 0x7f37cd663e3f in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x29e3f) (BuildId: 4f7b0c955c3d81d7cac1501a2498b69d1d82bfe7)
#3 0x55a1092f1114 in _start (/path/to/a.out+0x6f114)
SUMMARY: MemorySanitizer: use-of-uninitialized-value /path/to/test.cc:14:1 in main
Exiting
```
I can reproduce this on x86 and aarch64.
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