Can't get segmentation fault exit code from boost child process - c++11

Question

I am trying to get the exit code of a child process (using boost::process and boost::asio) when that child process is killed due to a segmentation violation or divide be zero or any other kill signal. The exit code and error code always return with 0 and success.
I am running this on CentOS 7 using g++ 4.8.5 and boost 1.66
If I run the same code with a child process that simply returns a non-zero exit code it successfully returns that exit code.
#include <iostream>
#include <boost/process.hpp>
#include <boost/asio/io_service.hpp>
namespace bp = boost::process;
using namespace std;
int main (int argc, char** argv)
{
string exe = "./crashes";
vector<string> data;
boost::asio::io_service ios;
int exit_code;
error_code ec;
future<string> ostr;
bp::child c(exe,
(bp::std_out & bp::std_err) > ostr,
ios,
bp::on_exit=[&exit_code, &ec](int exit, const error_code& ecin)
{exit_code = exit; ec = ecin;});
ios.run();
cout << "Exit Code = " << exit_code << endl;
cout << "Error Code = " << ec.message() << endl;
cout << "child stdin & stderr:\n";
cout << ostr.get() << endl;
return exit_code;
}
and the crashes code
int main (int argc, char** argv)
{
int* y = 0;
int c = *y;
}
The results show a 0 exit code and Success error_code
Exit Code = 0
Error Code = Success
child stdin & stderr:
running the crashes executable alone returns an exit code of 139
bash-4.2$ ./crashes
Segmentation fault (core dumped)
bash-4.2$ echo $?
139

Answer 1

The details of process termination and exit codes are platform dependent.
Boost process papers over the differences in the default interface: your on_exit handler is called with the result of boost::process::detail::posix::eval_exit_status() of the exit status, which means:
inline int eval_exit_status(int code)
{
if (WIFEXITED(code))
{
return WEXITSTATUS(code);
}
else if (WIFSIGNALED(code))
{
return WTERMSIG(code);
}
else
{
return code;
}
}
So, you get "exit-code 11" meaning segfault... If you want to actually know, you can look at native_exit_code()
bp::on_exit = [&result, &c](int /*ignored*/, const std::error_code &ec) {
auto exit_status = c.native_exit_code();
result.exit_code = boost::make_optional(WIFEXITED(exit_status), WEXITSTATUS(exit_status));
result.signal = boost::make_optional(WIFSIGNALED(exit_status), WTERMSIG(exit_status));
result.ec = ec;
}
Now this assumes some changes to the result variables. Full listing:
Listing
#include <boost/asio/io_service.hpp>
#include <boost/process.hpp>
#include <iostream>
namespace bp = boost::process;
int main(int argc, char**) {
std::string exe = argc>1? "./ltua" : "./crashes";
boost::asio::io_service ios;
struct {
boost::optional<int> exit_code;
boost::optional<int> signal;
std::error_code ec{};
} result;
std::future<std::string> ostr;
bp::group g;
bp::child c(exe, g, (bp::std_out & bp::std_err) > ostr, ios,
bp::on_exit = [&result, &c](int /*ignored*/, const std::error_code &ec) {
auto exit_status = c.native_exit_code();
result.exit_code = boost::make_optional(WIFEXITED(exit_status), WEXITSTATUS(exit_status));
result.signal = boost::make_optional(WIFSIGNALED(exit_status), WTERMSIG(exit_status));
result.ec = ec;
});
//g.wait();
ios.run();
if (result.exit_code) {
std::cout << "Exited with " << *result.exit_code << std::endl;
}
if (result.signal) {
std::cout << "Signaled with sginal #" << *result.signal << ", aka " << ::strsignal(*result.signal) << std::endl;
}
std::cout << "Error Code = " << result.ec.message() << std::endl;
std::cout << "child stdin & stderr:\n";
std::cout << ostr.get() << std::endl;
return result.exit_code? *result.exit_code : 255;
}
Output
When run with ltua.cpp:
#include <iostream>
int main() {
std::cout << "so long" << std::end;
std::cerr << "and thanks" << std::end;
std::cout << "for all" << std::end;
std::cerr << "the fish" << std::end;
return 42;
}
Prints
Exited with 42
Error Code = Success
child stdin & stderr:
so long
and thanks
for all
the fish
And with crashes.cpp:
int main() {
int *y = 0;
int c = *y;
}
Prints
Signaled with sginal #11, aka Segmentation fault
Error Code = Success
child stdin & stderr: