binutils-gdb/gdb/testsuite/gdb.base/step-over-clone.c
Andrew Burgess 99ba4b64d3 gdb/testsuite: update test gdb.base/step-over-syscall.exp
I was looking at PR gdb/19675 and the related test
gdb.base/step-over-syscall.exp.  This test includes a call to kfail
when we are testing a displaced step over a clone syscall.

While looking at the test I removed the call to kfail and ran the
test, and was surprised that the test passed.

I ran the test a few times and it does sometimes fail, but mostly it
passed fine.

PR gdb/19675 describes how, when we displaced step over a clone, the
new thread is created with a $pc in the displaced step buffer.  GDB
then fails to "fix" this $pc (for the new thread), and the thread will
be set running with its current $pc value.  This means that the new
thread will just start executing from whatever happens to be after the
displaced stepping buffer.

In the original PR gdb/19675 bug report Yao Qi was seeing the new
thread cause a segfault, the problem is, what actually happens is
totally undefined.

On my machine, I'm seeing the new thread reenter main, it then starts
trying to run the test again (in the new thread).  This just happens
to be safe enough (in this simple test) that most of the time the
inferior doesn't crash.

In this commit I try to make the test slightly more likely to fail by
doing a couple of things.

First, I added a static variable to main, this is set true when the
first thread enters main, if a second thread ever enters main then I
force an abort.

Second, when the test is finishing I want to ensure that the new
threads have had a chance to do "something bad" if they are going to.
So I added a global counter, as each thread starts successfully it
decrements the counter.  The main thread does not proceed to the final
marker function (where GDB has placed a breakpoint) until all threads
have started successfully.  This means that if the newly created
thread doesn't successfully enter clone_fn then the counter will never
reach zero and the test will timeout.

With these two changes my hope is that the test should fail more
reliably, and so, I have also changed the test to call setup_kfail
before the specific steps that we expect to misbehave instead of just
calling kfail and skipping parts of the test completely.  The benefit
of this is that if/when we fix GDB this test will start to KPASS and
we'll know to update this test to remove the setup_kfail call.
2021-08-05 10:44:16 +01:00

94 lines
2.6 KiB
C

/* This testcase is part of GDB, the GNU debugger.
Copyright 2016-2021 Free Software Foundation, Inc.
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>. */
#define _GNU_SOURCE
#include <stdlib.h>
#include <unistd.h>
#include <sched.h>
#include <pthread.h>
static void
marker ()
{}
#define STACK_SIZE 0x1000
/* These are used to signal that the threads have started correctly. The
GLOBAL_THREAD_COUNT is set to the number of threads in main, then
decremented (under a lock) in each new thread. */
pthread_mutex_t global_lock = PTHREAD_MUTEX_INITIALIZER;
int global_thread_count = 0;
static int
clone_fn (void *unused)
{
/* Signal that this thread has started correctly. */
if (pthread_mutex_lock (&global_lock) != 0)
abort ();
global_thread_count--;
if (pthread_mutex_unlock (&global_lock) != 0)
abort ();
return 0;
}
int
main (void)
{
int i, pid;
unsigned char *stack[6];
/* Due to bug gdb/19675 the cloned thread _might_ try to reenter main
(this depends on where the displaced instruction is placed for
execution). However, if we do reenter main then lets ensure we fail
hard rather then just silently executing the code below. */
static int started = 0;
if (!started)
started = 1;
else
abort ();
for (i = 0; i < (sizeof (stack) / sizeof (stack[0])); i++)
stack[i] = malloc (STACK_SIZE);
global_thread_count = (sizeof (stack) / sizeof (stack[0]));
for (i = 0; i < (sizeof (stack) / sizeof (stack[0])); i++)
{
pid = clone (clone_fn, stack[i] + STACK_SIZE, CLONE_FILES | CLONE_VM,
NULL);
}
for (i = 0; i < (sizeof (stack) / sizeof (stack[0])); i++)
free (stack[i]);
/* Set an alarm so we don't end up stuck waiting for threads that might
never start correctly. */
alarm (120);
/* Now wait for all the threads to start up. */
while (global_thread_count != 0)
{
/* Force memory barrier so GLOBAL_THREAD_COUNT will be refetched. */
asm volatile ("" ::: "memory");
sleep (1);
}
/* Call marker, this is what GDB is waiting for. */
marker ();
}