Debugging TV Frame 0x0C
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This document discusses debugging multiple exceptions that occur across threads. It presents code with two threads that each cause an exception by dereferencing a null pointer. The crash report shows that thread 2 crashed with an EXC_BAD_ACCESS exception. GDB output shows examining the crashed thread 2 and disassembling the code where it crashed.
![Multiple Exceptions
© 2012 DumpAnalysis.org + TraceAnalysis.org
void * thread_one (void *arg)
{
int *p = NULL;
*p = 1;
return 0;
}
void * thread_two (void *arg)
{
int *p = NULL;
*p = 2;
return 0;
}
int main(int argc, const char * argv[])
{
pthread_t threadID_one, threadID_two;
pthread_create (&threadID_one, NULL, thread_one, NULL);
pthread_create (&threadID_two, NULL, thread_two, NULL);
sleep(3);
return 0;
}](https://image.slidesharecdn.com/debuggingtvframe0x0c-171020154657/85/Debugging-TV-Frame-0x0C-3-320.jpg)
![GDB Output
© 2012 DumpAnalysis.org + TraceAnalysis.org
(gdb) info threads
3 0x00000001062ffe4e in thread_two (arg=0x0)
at /MultipleThreads/main.c:24
2 0x00000001062ffe1e in thread_one (arg=0x0)
at /MultipleThreads/main.c:16
* 1 0x00007fff854e0e42 in __semwait_signal ()
(gdb) thread 2
[Switching to thread 2 (core thread 1)]
0x00000001062ffe1e in thread_one (arg=0x0)
at /MultipleThreads/main.c:16
16 *p = 1;
(gdb) disassemble 0x00000001062ffe1e
Dump of assembler code for function thread_one:
0x00000001062ffe00 <thread_one+0>: push %rbp
0x00000001062ffe01 <thread_one+1>: mov %rsp,%rbp
0x00000001062ffe04 <thread_one+4>: mov $0x0,%rax
0x00000001062ffe0e <thread_one+14>: mov %rdi,-0x8(%rbp)
0x00000001062ffe12 <thread_one+18>: movq $0x0,-0x10(%rbp)
0x00000001062ffe1a <thread_one+26>: mov -0x10(%rbp),%rdi
0x00000001062ffe1e <thread_one+30>: movl $0x1,(%rdi)
0x00000001062ffe24 <thread_one+36>: pop %rbp
0x00000001062ffe25 <thread_one+37>: retq
End of assembler dump.
(gdb) info registers rdi
rdi 0x0 0](https://image.slidesharecdn.com/debuggingtvframe0x0c-171020154657/85/Debugging-TV-Frame-0x0C-5-320.jpg)
Debugging TV Frame 0x0C
- 1. Frame 0x0C Presenter: Dmitry Vostokov Sponsors Debugging.TV
- 2. • Multithreading • Multiple exceptions • Diagnostic Console reports • GDB commands for thread navigation Topics © 2012 DumpAnalysis.org + TraceAnalysis.org
- 3. Multiple Exceptions © 2012 DumpAnalysis.org + TraceAnalysis.org void * thread_one (void *arg) { int *p = NULL; *p = 1; return 0; } void * thread_two (void *arg) { int *p = NULL; *p = 2; return 0; } int main(int argc, const char * argv[]) { pthread_t threadID_one, threadID_two; pthread_create (&threadID_one, NULL, thread_one, NULL); pthread_create (&threadID_two, NULL, thread_two, NULL); sleep(3); return 0; }
- 4. Crash Report © 2012 DumpAnalysis.org + TraceAnalysis.org Crashed Thread: 2 Exception Type: EXC_BAD_ACCESS (SIGSEGV) Exception Codes: KERN_INVALID_ADDRESS at 0x0000000000000000 Thread 0:: Dispatch queue: com.apple.main-thread 0 libsystem_kernel.dylib 0x00007fff854e0e42 __semwait_signal + 10 1 libsystem_c.dylib 0x00007fff8ababdea nanosleep + 164 2 libsystem_c.dylib 0x00007fff8ababc2c sleep + 61 3 MultipleThreads 0x000000010f523ec3 main + 99 (main.c:36) 4 MultipleThreads 0x000000010f523df4 start + 52 Thread 1: 0 MultipleThreads 0x000000010f523e1e thread_one + 30 (main.c:16) 1 libsystem_c.dylib 0x00007fff8abf58bf _pthread_start + 335 2 libsystem_c.dylib 0x00007fff8abf8b75 thread_start + 13 Thread 2 Crashed: 0 MultipleThreads 0x000000010f523e4e thread_two + 30 (main.c:24) 1 libsystem_c.dylib 0x00007fff8abf58bf _pthread_start + 335 2 libsystem_c.dylib 0x00007fff8abf8b75 thread_start + 13 Thread 2 crashed with X86 Thread State (64-bit): rax: 0x0000000000000000 rbx: 0x0000000000000000 rcx: 0x00007fff854e10c2 rdx: 0x0000000000000000 rdi: 0x0000000000000000 rsi: 0x0000000000000000 rbp: 0x000000010f780f10 rsp: 0x000000010f780f10 r8: 0x00007fff754c3fb8 r9: 0x0000000000000001 r10: 0x00007fff8abf8b94 r11: 0x0000000000000202 r12: 0x0000000000001303 r13: 0x000000010f781000 r14: 0x0000000000000000 r15: 0x000000010f523e30 rip: 0x000000010f523e4e rfl: 0x0000000000010217 cr2: 0x0000000000000000
- 5. GDB Output © 2012 DumpAnalysis.org + TraceAnalysis.org (gdb) info threads 3 0x00000001062ffe4e in thread_two (arg=0x0) at /MultipleThreads/main.c:24 2 0x00000001062ffe1e in thread_one (arg=0x0) at /MultipleThreads/main.c:16 * 1 0x00007fff854e0e42 in __semwait_signal () (gdb) thread 2 [Switching to thread 2 (core thread 1)] 0x00000001062ffe1e in thread_one (arg=0x0) at /MultipleThreads/main.c:16 16 *p = 1; (gdb) disassemble 0x00000001062ffe1e Dump of assembler code for function thread_one: 0x00000001062ffe00 <thread_one+0>: push %rbp 0x00000001062ffe01 <thread_one+1>: mov %rsp,%rbp 0x00000001062ffe04 <thread_one+4>: mov $0x0,%rax 0x00000001062ffe0e <thread_one+14>: mov %rdi,-0x8(%rbp) 0x00000001062ffe12 <thread_one+18>: movq $0x0,-0x10(%rbp) 0x00000001062ffe1a <thread_one+26>: mov -0x10(%rbp),%rdi 0x00000001062ffe1e <thread_one+30>: movl $0x1,(%rdi) 0x00000001062ffe24 <thread_one+36>: pop %rbp 0x00000001062ffe25 <thread_one+37>: retq End of assembler dump. (gdb) info registers rdi rdi 0x0 0
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