[PATCH v2 2/6] gdb/infrun: in condition evaluation resume only current thread.

[Natalia Saiapova <natalia.saiapova@intel.com>]

When stopped at a conditional BP, GDB evaluates the condition for the
event thread in order to decide whether the thread should be stopped or
resumed.  Thus, if the condition includes an inferior call, during
the call not all threads have finalized state, some of them might
still be shown as running.  While executing the proceed for the inferior
call, GDB tries to resume all non-exited threads.  This leads to
the following assertion, when GDB tries to resume a running thread:

    (gdb) b 43 if foo()
    Breakpoint 1 at 0x119b: file main.c, line 43.
    (gdb) run
    Starting program: main
    [Thread debugging using libthread_db enabled]
    Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
    [New Thread 0x7ffff77c4700 (LWP 21421)]
    [New Thread 0x7ffff6fc3700 (LWP 21422)]
    gdb/nat/x86-linux-dregs.c:146: internal-error: void x86_linux_update_debug_registers(lwp_info*): Assertion `lwp_is_stopped (lwp)' failed.
    A problem internal to GDB has been detected,
    further debugging may prove unreliable.

    This is a bug, please report it.  For instructions, see:
    <https://www.gnu.org/software/gdb/bugs/>.

This patch changes the behavior, so if the current thread is in the
middle of a condition evaluation, only the current thread is resumed.

gdb/ChangeLog:
2020-08-26  Natalia Saiapova  <natalia.saiapova@intel.com>
	    Tankut Baris Aktemur <tankut.baris.aktemur@intel.com>

	* infrun.c (user_visible_resume_ptid): In BP condition
	evaluation, resume only the current thread

Co-authored-by: Natalia Saiapova <natalia.saiapova@intel.com>
Co-authored-by: Tankut Baris Aktemur <tankut.baris.aktemur@intel.com>

Signed-off-by: Natalia Saiapova <natalia.saiapova@intel.com>
---
 gdb/infrun.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/gdb/infrun.c b/gdb/infrun.c
index d552fb3adb2..91271c2ddbe 100644
--- a/gdb/infrun.c
+++ b/gdb/infrun.c
@@ -2156,6 +2156,14 @@ user_visible_resume_ptid (int step)
 	 mode.  */
       resume_ptid = inferior_ptid;
     }
+  else if (inferior_ptid != null_ptid
+	   && inferior_thread ()->control.in_cond_eval)
+    {
+      /* The inferior thread is evaluating a BP condition.  Other threads
+	 might be stopped or running and we do not want to change their
+	 state, thus, resume only the current thread.  */
+      resume_ptid = inferior_ptid;
+    }
   else if (!sched_multi && target_supports_multi_process ())
     {
       /* Resume all threads of the current process (and none of other
-- 
2.17.1

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