landonf · June 17, 2011 22:51
diff --git a/stackoverflow.m b/stackoverflow.m
 #import <Foundation/Foundation.h>

 #import <pthread.h>
 #import <execinfo.h>
 #import <string.h>
 #import <stdint.h>

 /*
 * A signal handler that is broken in two ways:
 * 1) The handler calls APIs that are not declared to be async-safe and may deadlock or otherwise fail.
 * 2) The handler can not capture a backtrace should the stack overflow.
 */
 static void unsafe_signal_handler (int signo) {
    signal(signo, SIG_DFL);

    /* Attempt to use backtrace(3) to fetch the backtrace. This requires that we be
     * operating on the crashed thread's stack, but that stack just overflowed,
     * and our signal handler will simply crash.
     *
     * However, if we used sigaltstack() to correctly run on a different stack, our
     * backtrace would be empty! This is not limited to backtrace(3) -- [NSThread callStackReturnAddresses]
     * will exhibit the same behavior.
     *
     * This is one reason why backtraces must be implemented by implementing your own stack walking
     * using the ucontext_t from the SA_SIGINFO prototype.
     */
    void *callstack[128];
    int count = backtrace(callstack, 128);
    backtrace_symbols_fd(callstack, count, STDERR_FILENO);
 }

 int main(int argc, char *argv[]) {
    NSAutoreleasePool *pool = [NSAutoreleasePool new];

    /* Set up the signal handler. */
    signal(SIGABRT, unsafe_signal_handler);
    signal(SIGSEGV, unsafe_signal_handler);
    
    /* Run some buggy code in an unusual code path. A small typo will trigger infinite recursion ... */
    NSArray *resultMessages = [NSMutableArray arrayWithObject: @"Error message!"];
    NSMutableArray *results = [[NSMutableArray alloc] init];

    for (NSObject *result in resultMessages)
        [results addObject: results]; // Whoops!

    NSLog(@"Some strange unexpected error we never see occured with results: %@", results);

    [pool drain];
    return 0;
 }
	#import <Foundation/Foundation.h>

	#import <pthread.h>
	#import <execinfo.h>
	#import <string.h>
	#import <stdint.h>

	/*
	* A signal handler that is broken in two ways:
	* 1) The handler calls APIs that are not declared to be async-safe and may deadlock or otherwise fail.
	* 2) The handler can not capture a backtrace should the stack overflow.
	*/
	static void unsafe_signal_handler (int signo) {
	signal(signo, SIG_DFL);

	/* Attempt to use backtrace(3) to fetch the backtrace. This requires that we be
	* operating on the crashed thread's stack, but that stack just overflowed,
	* and our signal handler will simply crash.
	*
	* However, if we used sigaltstack() to correctly run on a different stack, our
	* backtrace would be empty! This is not limited to backtrace(3) -- [NSThread callStackReturnAddresses]
	* will exhibit the same behavior.
	*
	* This is one reason why backtraces must be implemented by implementing your own stack walking
	* using the ucontext_t from the SA_SIGINFO prototype.
	*/
	void *callstack[128];
	int count = backtrace(callstack, 128);
	backtrace_symbols_fd(callstack, count, STDERR_FILENO);
	}

	int main(int argc, char *argv[]) {
	NSAutoreleasePool *pool = [NSAutoreleasePool new];

	/* Set up the signal handler. */
	signal(SIGABRT, unsafe_signal_handler);
	signal(SIGSEGV, unsafe_signal_handler);

	/* Run some buggy code in an unusual code path. A small typo will trigger infinite recursion ... */
	NSArray *resultMessages = [NSMutableArray arrayWithObject: @"Error message!"];
	NSMutableArray *results = [[NSMutableArray alloc] init];

	for (NSObject *result in resultMessages)
	[results addObject: results]; // Whoops!

	NSLog(@"Some strange unexpected error we never see occured with results: %@", results);

	[pool drain];
	return 0;
	}