Deadlocking a signal handler by using ObjC (ARM / x86-32)

deadlock.m

#import <Foundation/Foundation.h>

static void unsafe_signal_handler (int signo) {
    signal(signo, SIG_DFL);
    
    /* Attempt to use ObjC to fetch the backtrace. Will trigger deadlock. */
    [NSThread callStackSymbols];
}

int main(int argc, char *argv[]) {
    signal(SIGSEGV, unsafe_signal_handler);
    
    void *cache[] = {
        NULL, NULL, NULL
    };

    /* Some random data array */
    void *displayStrings[6] = {
        "This little piggy went to the market",
        "This little piggy stayed at home",
        cache, 
        "This little piggy had roast beef.",
        "This little piggy had none.",
        "And this little piggy went 'Wee! Wee! Wee!' all the way home",
    };
    
    /* A corrupted/under-retained/re-used piece of memory */
    struct {
        void *isa;
    } corruptObj;
    corruptObj.isa = displayStrings;
    
    /* Attempting to message an invalid/corrupt object */
    [(id)&corruptObj class];
    
    return 0;
}