[Bug c++/48854] New: signal mask is not restored when exiting signal handler via exception

[cubbi at cubbi dot org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48854

           Summary: signal mask is not restored when exiting signal
                    handler via exception
           Product: gcc
           Version: 4.6.0
            Status: UNCONFIRMED
          Severity: trivial
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: cubbi@cubbi.org


When using -fnon-call-exception to convert a SIGSEGV or SIGFPE to a C++
exception, the straightforward implementation fails to handle the same signal
more than once because it remains masked after the signal handler and the
exception handler have been executed.

While this is reasonable behavior, perhaps it should be briefly mentioned in
the documentation on -fnon-call-exceptions?

Example (compile with -fnon-call-exceptions)

#include <iostream>
#include <stdexcept>
#include <signal.h>
void handler(int signo)
{
    std::cerr << "Signal handler called with " << signo << '\n';

    // uncomment the following lines to fix the bug
    // sigset_t x;
    // sigemptyset (&x);
    // sigaddset(&x, SIGSEGV);
    // sigprocmask(SIG_UNBLOCK, &x, NULL);

    throw std::runtime_error("sigsegv");
}

int main()
{
    signal(SIGSEGV, handler);
    int* invalid_p = NULL;

    // first attempt: always works
    try{
        *invalid_p = 7;
    } catch(const std::exception& e)
    {
        std::cerr << "main() caught " << e.what() << '\n';
    }

    // second attempt: fails unless uncommented sigprocmask above
    try{
        *invalid_p = 7;
    } catch(const std::exception& e)
    {
        std::cerr << "main() caught " << e.what() << '\n';
    }
}

reproduced using
gcc 3.4.6 (linux x86_64)
gcc 4.4.1 (linux i386)
gcc 4.5.2 (linux x86_64)
gcc 4.6.0 20110325 (linux x86_64)