https://gcc.gnu.org/bugzilla/show_bug.cgi?id=125225
Bug ID: 125225
Summary: ASan finds an ODR violation in piecewise_construct
with -flto=auto
Product: gcc
Version: 16.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: stuart.a.hayhurst at gmail dot com
Target Milestone: ---
When compiling a shared library that contains a global unordered_map in an
anonymous namespace and a binary that uses the shared library and also contains
a global unordered_map in an anonymous namespace, ASan finds an ODR violation.
This only happens when -flto=auto is used, and doesn't happen with clang. The
code compiles just fine with -Wall -Wextra -Werror -Wpedantic.
Currently running G++ 16.0.1 20260425 on Debian Sid, but this also happened
with the G++ 15 series.
Let me know if you need any more information :)
Compiled with:
CXX=g++
CXXFLAGS="-std=c++20 -flto=auto -fsanitize=address"
$CXX a.cpp -c $CXXFLAGS -o a.o
$CXX b.cpp -c $CXXFLAGS -fpic -o b.o
$CXX -shared -o libb.so b.o $CXXFLAGS -fpic "-Wl,-soname,libb.so"
$CXX -o demo a.o $CXXFLAGS -L./ -lb
LD_LIBRARY_PATH="$LD_LIBRARY_PATH:./" ./demo
Couldn't figure out how to attach multiple files, so I'll paste the reproducer
below:
a.cpp:
```
#include <unordered_map>
namespace {
std::unordered_map<int, bool> example_map = {
{1, {true}}
};
}
int main() {
return example_map[1];
}
```
b.cpp:
```
#include <iostream>
#include <unordered_map>
namespace {
std::unordered_map<int, bool> example_map = {
{1, {true}}
};
}
namespace exposed {
void something() {
std::cout << example_map[1] << std::endl;
}
}
```
