Re: [issues] arm gdb backtrace for read syscall

[Matthieu CASTET <matthieu.castet@xxxxxxxxxx>]

Carlos O'Donell a écrit :
> On Mon, Oct 20, 2008 at 4:23 AM, Matthieu CASTET
> <matthieu.castet@xxxxxxxxxx> wrote:
>>> Could you describe the behaviour you would like?
>> I would like that when a process is block on the read system call, I can
>> get the complete backtrace ie getting caller of the read syscall.
>> This is the case for example for sigwaitinfo syscall.
> 
> Please provide a test-case.
> 
Ok here a testcase. /tmp/fifo could be a fifo, an uart or whatever you like.
For info with gdb 6.8, I got [1].


Matthieu

Note that not memseting 'buff' leads to different results (ie we got the
dl_resolver call in the backtrace).

[1]

(gdb) info threads
[New Thread 723]
  2 Thread 723  0x40033844 in read ()
   from /opt/arm-eglibc/arm-none-linux-gnueabi/libc/lib/libpthread.so.0
* 1 Thread 722  0x4002b8b8 in pthread_join (threadid=0x4095d490,
    thread_return=0xbecfdd64) at pthread_join.c:89
(gdb) thread 2
[Switching to thread 2 (Thread 723)]#0  0x40033844 in read ()
   from /opt/arm-eglibc/arm-none-linux-gnueabi/libc/lib/libpthread.so.0
Current language:  auto; currently asm
(gdb) bt
#0  0x40033844 in read ()
   from /opt/arm-eglibc/arm-none-linux-gnueabi/libc/lib/libpthread.so.0
#1  0x400330ac in __pthread_enable_asynccancel () at cancellation.c:42
#2  0x00000000 in ?? ()

#include <pthread.h>
#include <assert.h>
#include <limits.h>
#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>


/* to be build with gcc -O0 -g -lpthread

*/

#define CHECK(x) do { \
		assert(x==0); \
	} while (0)

void *reader(void *data)
{
	char buff [10];
	int fd = open("/tmp/fifo", O_RDONLY);
	/* clean the stack */
	memset(buff, 0, 10);
	while (1) {
		if (fd != -1) {
			read(fd, buff, 1);
		}
	}
}

void launch_thread(pthread_attr_t *attr, void *(*start_routine)(void *))
{
	size_t guardsize;
	size_t stacksize;
	pthread_t thandle;
	void *ret;
	int res;

	printf("creating thread %p\n", start_routine);
	res = pthread_create(&thandle, attr, start_routine, NULL);
	printf("done with status %d %s\n", res, strerror(res));
	if (res == 0) {
		CHECK(pthread_join(thandle, &ret));
	}
}

int main()
{
	launch_thread(NULL, reader);
	return 0;
}