| Issue |
76771
|
| Summary |
strange C++ unwind behavior on ppc64le with LTO program and -ftrivial-auto-var-init=zero libunwind
|
| Labels |
new issue
|
| Assignees |
|
| Reporter |
q66
|
Clang 17.0.6, ppc64le, musl libc, compiler-rt/libunwind/libc++, Chimera Linux.
Given the following program C++:
```
#include <cstdio>
#include <stdexcept>
#include <string>
using str = std::string;
int main(void) {
printf("iter 1\n");
if (true) {
str foo1{"some random string"};
try {
throw std::runtime_error{"some random string"};
} catch (std::runtime_error const &e) {
if (foo1 != e.what()) {
printf("BOO! '%s' '%s' %p\n", e.what(), foo1.data(), foo1.data());
}
printf("OK %p\n", foo1.data());
}
}
printf("iter 2\n");
if (true) {
str foo2{"some random string"};
try {
throw std::runtime_error{"some random string"};
} catch (std::runtime_error const &e) {
if (foo2 != e.what()) {
printf("BOO! '%s' '%s' %p\n", e.what(), foo2.data(), foo2.data());
}
printf("OK %p\n", foo2.data());
}
}
}
```
I get the following output:
```
iter 1
OK 0x3fffc2943891
iter 2
BOO! 'some random string' 'dom strisome ranng' 0x3fffc2943891
OK 0x3fffc2943891
```
When compiled with the following flags: `-O2 -flto=thin`, but particularly only when libunwind is compiled with `-ftrivial-auto-var-init=zero`. The prerequisite is always this combo; if I either compile the test program without LTO, or if I compile libunwind without any special flags, the test program works. It's always the second iteration that breaks. I am not sure whether this is a miscompilation problem of the test program, or of libunwind itself.
This was originally found by running the test suite of the `fmt` library, where the `ostream` tests fail like this. It's always every second throw, i.e. in a program with 4 iterations, two of them fail.
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