Re: [patch] Fix TLS access for -static -pthread

[Yao Qi <yao@codesourcery.com>]

On 06/05/2014 04:06 PM, Jan Kratochvil wrote:
>> This patch is to set another breakpoint at the end of main, so that
>> > main thread will hit it, and we can check the value of tlsvar then.
>> > It is safe and we don't have to worry about whether gdb is able to
>> > unwind from pthread library to main function or not.
> I have to warn that it may be a bit weaker test, it never tests both threads
> TLS access during the same stop, it tests only the current thread.
> 
> But it still tests the patch works so I am fine with it (not an approval).
> 

The patch below is to keep testing TLS access in one stop, and
work around the bug of unwinding clone.  WDYT?

-- 
Yao (齐尧)

Subject: [PATCH] Fix the race in gdb.threads/staticthreads.exp

The code in gdb.threads/staticthreads.exp about checking the value of
tlsvar in main thread is racy, because when child thread hits
breakpoint, the main thread may not go into pthread_join yet, and
may not be unwind to main.

This patch is to move the line setting breakpoint on after sem_wait,
so that the child thread will hit breakpoint after main thread calls
sem_post.  IOW, when child thread hits breakpoint, the main thread is
in either sem_post or pthread_join.  "up 10" can unwind main thread to
main.

gdb/testsuite:

2014-06-05  Yao Qi  <yao@codesourcery.com>

	* gdb.threads/staticthreads.c (thread_function): Move the line
	setting breakpoint on forward.
	* gdb.threads/staticthreads.exp: Update comments.
---
 gdb/testsuite/gdb.threads/staticthreads.c   | 2 +-
 gdb/testsuite/gdb.threads/staticthreads.exp | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/gdb/testsuite/gdb.threads/staticthreads.c b/gdb/testsuite/gdb.threads/staticthreads.c
index 5c8eabe..db78063 100644
--- a/gdb/testsuite/gdb.threads/staticthreads.c
+++ b/gdb/testsuite/gdb.threads/staticthreads.c
@@ -38,7 +38,6 @@ thread_function (void *arg)
 #ifdef HAVE_TLS
   tlsvar = 2;
 #endif
-  printf ("Thread executing\n"); /* tlsvar-is-set */
   while (sem_wait (&semaphore) != 0)
     {
       if (errno != EINTR)
@@ -47,6 +46,7 @@ thread_function (void *arg)
 	  return NULL;
 	}
     }
+  printf ("Thread executing\n"); /* tlsvar-is-set */
   return NULL;
 }
 
diff --git a/gdb/testsuite/gdb.threads/staticthreads.exp b/gdb/testsuite/gdb.threads/staticthreads.exp
index 9fa625a..bdc03d4 100644
--- a/gdb/testsuite/gdb.threads/staticthreads.exp
+++ b/gdb/testsuite/gdb.threads/staticthreads.exp
@@ -105,7 +105,7 @@ if { "$have_tls" != "" } {
     gdb_continue_to_breakpoint "tlsvar-is-set" ".* tlsvar-is-set .*"
     gdb_test "p tlsvar" " = 2" "tlsvar in thread"
     gdb_test "thread 1" ".*"
-    # Unwind from pthread_join.
+    # Unwind to main.
     gdb_test "up 10" " in main .*"
     gdb_test "p tlsvar" " = 1" "tlsvar in main"
 }
-- 
1.9.0