gdbserver: move_out_of_jump_pad_callback misses switching current thread

While hacking on the fix for PR threads/18600 (Threads left stopped
after fork+thread spawn), I once saw its test (fork-plus-threads.exp)
FAIL against gdbserver because move_out_of_jump_pad_callback has a
gdb_breakpoint_here call, and the caller isn't making sure the current
thread points to the right thread.  In the case I saw, the current
thread pointed to the wrong process, so gdb_breakpoint_here returned
the wrong answer.  Unfortunately I didn't save logs.  Still, seems
obvious enough and it should fix a potential occasional racy FAIL.

Tested on x86_64 Fedora 20.

gdb/gdbserver/ChangeLog:
2015-08-06  Pedro Alves  <palves@redhat.com>

	* linux-low.c (move_out_of_jump_pad_callback): Temporarily switch
	the current thread.

diff --git a/gdb/gdbserver/ChangeLog b/gdb/gdbserver/ChangeLog
index d03d1f6b2f4cbcfc9fa2aa6eee57fa2f75cb23cd..d035aaeb4b2e1dcee1699aa6e04112c8e664135d 100644 (file)
--- a/gdb/gdbserver/ChangeLog
+++ b/gdb/gdbserver/ChangeLog
@@ -1,3 +1,8 @@
+2015-08-06  Pedro Alves  <palves@redhat.com>
+
+       * linux-low.c (move_out_of_jump_pad_callback): Temporarily switch
+       the current thread.
+
 2015-08-06  Pedro Alves  <palves@redhat.com>
 
        * linux-low.c (linux_write_memory): Rewrite debug output to avoid

diff --git a/gdb/gdbserver/linux-low.c b/gdb/gdbserver/linux-low.c
index 57e4eba2e66b2cf1c934cdb1894f8aa9ba88a7ab..a229c5018d360696bda07eae6a978cfdf1173164 100644 (file)
--- a/gdb/gdbserver/linux-low.c
+++ b/gdb/gdbserver/linux-low.c
@@ -3646,6 +3646,7 @@ static void
 move_out_of_jump_pad_callback (struct inferior_list_entry *entry)
 {
   struct thread_info *thread = (struct thread_info *) entry;
+  struct thread_info *saved_thread;
   struct lwp_info *lwp = get_thread_lwp (thread);
   int *wstat;
 
@@ -3657,6 +3658,10 @@ move_out_of_jump_pad_callback (struct inferior_list_entry *entry)
     }
   gdb_assert (lwp->stopped);
 
+  /* For gdb_breakpoint_here.  */
+  saved_thread = current_thread;
+  current_thread = thread;
+
   wstat = lwp->status_pending_p ? &lwp->status_pending : NULL;
 
   /* Allow debugging the jump pad, gdb_collect, etc.  */
@@ -3684,6 +3689,8 @@ move_out_of_jump_pad_callback (struct inferior_list_entry *entry)
     }
   else
     lwp_suspended_inc (lwp);
+
+  current_thread = saved_thread;
 }
 
 static int