Bug#827015: libunwind8: Linking with Libwunind leads to corrupt process signal mask if exception thrown in c++

[Marc Strämke]

Package: libunwind8
Version: 1.1-4.1
Severity: important

Dear Maintainer,

linking c++ Programs with libunwind leads to corruption of the process signal
mask as soon as an exception is thrown.

Since 1.0.1-3 libunwind is configured with --enable-cxx-exceptions. As soon as
one links with libunwind it does get called every exception thrown.
Which is Probably not what the user expects. Without rebuilding libunwind
cannot be used for any of its other functionality without
also handling all c++ exceptions.

During exception handling the following problem appears:
Without libunwind the sample program works as expected:

# g++  -o sigtest visu/sigtest.cpp  -lpthread
# ./sigtest
Signals blocked: 1 (Hangup)     65 (Unknown signal 65)
Throw exception
Signals blocked: 1 (Hangup)     65 (Unknown signal 65)


With libunwind:

# g++  -o sigtest visu/sigtest.cpp  -lpthread -lunwind
# ./sigtest
Signals blocked: 1 (Hangup)     65 (Unknown signal 65)
Throw exception
Signals blocked: 4 (Illegal instruction)        7 (Bus error)   10 (User
defined signal 1)      12 (User defined signal 2)      13 (Broken pipe)
14 (Alarm clock)        17 (Child exited)       18 (Continued)  24 (CPU time
limit exceeded) 25 (File size limit exceeded)   28 (Window changed)     34
(Real-time signal 0) 37 (Real-time signal 3) 38 (Real-time signal 4) 41 (Real-
time signal 7) 42 (Real-time signal 8) 43 (Real-time signal 9) 44 (Real-time
signal 10)    45 (Real-time signal 11) 46 (Real-time signal 12)        47
(Real-time signal 13)        65 (Unknown signal 65)





-- System Information:
Debian Release: stretch/sid
  APT prefers testing
  APT policy: (500, 'testing')
Architecture: amd64 (x86_64)
Foreign Architectures: i386

Kernel: Linux 4.5.0-2-amd64 (SMP w/8 CPU cores)
Locale: LANG=de_DE.UTF-8, LC_CTYPE=de_DE.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)

Versions of packages libunwind8 depends on:
ii  libc6     2.22-9
ii  liblzma5  5.1.1alpha+20120614-2.1

libunwind8 recommends no packages.

libunwind8 suggests no packages.

#include <stdexcept>
#include <signal.h>
#include <string.h>
#include <stdio.h>

void function_that_throw() {
    printf("Throw exception\n");
    throw std::runtime_error("Exception");
}

void printSigMask() {
    sigset_t currmask;
    sigprocmask(SIG_BLOCK, NULL, &currmask);
    printf("Signals blocked: ");
    for (int sig = 1; sig <= NSIG; sig++) {
        if (sigismember(&currmask, sig)) {
            printf("%d (%s)\t", sig, strsignal(sig));
        }
    }
    printf("\n");
}

int main(int ac, char *av[]) {
    sigset_t sigset;

    sigemptyset(&sigset);
    sigaddset(&sigset, SIGHUP);
    pthread_sigmask(SIG_BLOCK, &sigset, NULL);

    printSigMask();
    try {
        function_that_throw();
    } catch (std::exception &excp) {
    }

    printSigMask();
}