https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110635
Bug ID: 110635
Summary: Segmentation fault when the awaiter's await_resume in
initial-suspend returns a class type.
Product: gcc
Version: 13.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: eustrain at outlook dot com
Target Milestone: ---
The simplest code here:
#include <coroutine>
struct Coroutine {
struct promise_type;
using handler_type = std::coroutine_handle<promise_type>;
struct initial_suspend_awaiter {
bool await_ready() noexcept { return false; }
void await_suspend(handler_type h) noexcept { }
using await_resume_return_object = struct{}; // bad
// using await_resume_return_object = int; // ok
await_resume_return_object await_resume() noexcept { return {}; }
initial_suspend_awaiter() noexcept { }
~initial_suspend_awaiter() noexcept { }
};
struct promise_type {
void return_void() noexcept {}
void unhandled_exception() noexcept { }
initial_suspend_awaiter initial_suspend() noexcept { return {}; }
std::suspend_never final_suspend() noexcept { return {}; }
Coroutine get_return_object() { return
Coroutine{handler_type::from_promise(*this)}; }
};
handler_type handler;
};
int main() {
auto coro = []()->Coroutine { co_return; }();
coro.handler.resume();
}
The C++ standard said, a coroutine behaves as if its function-body were
replaced by:
{
promise-type promise promise-constructor-arguments ;
try {
co_await promise.initial_suspend() ;
<function-body>
} catch ( ... ) {
if (!initial-await-resume-called)
throw ;
promise.unhandled_exception() ;
}
final-suspend :
co_await promise.final_suspend() ;
}
So, the result of "promise-type promise promise-constructor-arguments" will be
discarded. However, when it returns the class type, gcc will get a segmentation
fault.
The complete test code: https://godbolt.org/z/dG8q9GGj8
You can modify the CASE macro to adjust the return type in that code.
The bug is also occur in clang in a somewhat different situation.
https://github.com/llvm/llvm-project/issues/63803
