c++c++20c++-modules

Program crashes when using modules partitions and implementation units

I have following program:

#include <cstdio>

import animal;

int main() {
 auto s = makeSound();
 printf("%s", s.c_str());
 return 0;
}

and module interface:

module;
#include <string>
export module animal;
import :sound;

export std::string makeSound() {
 return makeSound_Impl();
}

and module implementation unit:

module;

#include <string>

module animal:sound;

std::string makeSound_Impl() {
 return "Wroooarrh";
}

Program is compiled with:

g++ -fmodules-ts -g -std=c++20 animal_sound.cpp -c -o animal_sound.o
g++ -fmodules-ts -g -std=c++20 animal.cpp -c -o animal.o
g++ -fmodules-ts -g -std=c++20 animal.o animal_sound.o main.cpp -o main.exe

Compiler version:

g++ --version
g++ (Ubuntu 13.1.0-8ubuntu1~22.04) 13.1

Program crashes on basic_string:

Program received signal SIGSEGV, Segmentation fault.
0x00005555555566c2 in std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >::_M_data (this=0xd00aa32b9e55bf00) at /usr/include/c++/13/bits/basic_string.h:223
223           { return _M_dataplus._M_p; }
(gdb) bt
#0  0x00005555555566c2 in std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >::_M_data (this=0x0) at /usr/include/c++/13/bits/basic_string.h:223
#1  0x0000555555556f3a in std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >::c_str (this=0x7fffffffda50) at /usr/include/c++/13/bits/basic_string.h:2584
#2  0x0000555555556ea6 in main () at main.cpp:7

When compiled with module 'animal' defining makeSound directly (not working as proxy to implementation unit):

module;
#include <string>
export module animal;

export std::string makeSound() {
 return "Sound!";
}

Everything works fine (program does not crash). Am I doing something wrong, or that's a compiler issue?

EDIT

Interestingly I was able to reproduce the issue without implementation units. If no include <string> is present in module 'animal' then problem is gone.

module;
#include <string>
export module animal:sound;

export std::string makeSound() {
 return "Wroooarrh";
}

module;
// #include <string>  // Adding include makes program crash
export module animal;
export import :sound;

EDI2

Reported bug on GCC Bugzilla: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111447

Solution

  • The problem you seem to be having is due to each of the module units in the same module having a #include <string> in them. This should not be a problem; there should be nothing wrong with different module units in the same module including the same header in their global module fragments. But your compiler won't seem to let you do it.

    That makes it a compiler bug.