| Issue |
134515
|
| Summary |
[msan] Runtime false positives with iostream, msan, and -O0
|
| Labels |
new issue
|
| Assignees |
|
| Reporter |
steveWang
|
Running clang version 19.1.7 obtained from Arch Linux repositories, with libc++ 19.1.7-1 and libstdc++ 14.2.1, although this also reproduces on Compiler Explorer with newer versions of clang.
I was exploring the conditions in which MSAN / ASAN / hardened builds detect buffer overruns (initially exploring with std::array which stores its data inline), and ran into the following issues with printing argc:
```c++
// $ clang++ -fsanitize=memory
#include <iostream>
#include <vector>
int main(int argc, char** argv) {
std::vector<int> vec = {1, 2, 3, 4};
std::cout << argc << std::endl;
return 0;
}
```
https://godbolt.org/z/ovxsG8e9d
(I was initially modifying vec[argc], but removed that when constructing a reproducer to make sure that wasn't a confounding factor.)
In short: with libc++, this fails when trying to format argc, while with libstdc++, this fails when printing _any_ string.
In the latter case, I've gotten this down to the following minimum reproducer on Compiler Explorer, but it doesn't reproduce locally:
```c++
// $ clang++ -stdlib=libc++ -fsanitize=memory
#include <iostream>
int main(int argc, char** argv) {
std::cout << "hello world\n";
return 0;
}
```
https://godbolt.org/z/3Ea9coP3E
![]()
_______________________________________________
llvm-bugs mailing list
llvm-bugs@lists.llvm.org
https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-bugs
