Read stop_pc after updating the gdbarch when exec'ing

When an inferior execs and changes architecture (e.g. 64 bits to 32
bits), the gdbarch associated to the inferior is updated by the
follow_exec call in handle_inferior_event_1.  We should avoid doing any
register read before that point, because the registers sent by the
remote side will be those of the new architecture, but we would
interpret them using the old architecture.  We do just that by setting
stop_pc during this window, which obviously requires reading the
registers.  This results in gdb.multi/multi-arch-exec.exp failing, GDB
outputting the following error:

  Truncated register 50 in remote 'g' packet

This patch fixes that by postponing the setting of stop_pc to after
we've updated the inferior gdbarch.

This bug was hiding another problem, and as such introduces some
failures in gdb.base/foll-exec-mode.exp.  The following patch takes care
of that.

gdb/ChangeLog:

	* infrun.c (handle_inferior_event_1): When exec'ing, read
	stop_pc after follow_exec.

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 27922083662c3131e744a0d9583a641e736ead63..2fe8ab103f7d17341a1581a615c3c035d34bccc3 100644 (file)
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,8 @@
+2017-09-05  Simon Marchi  <simon.marchi@ericsson.com>
+
+       * infrun.c (handle_inferior_event_1): When exec'ing, read
+       stop_pc after follow_exec.
+
 2017-09-05  Simon Marchi  <simon.marchi@ericsson.com>
 
        * remote.c (process_g_packet): Update error message.

diff --git a/gdb/infrun.c b/gdb/infrun.c
index 7568a5ef478df3ef168827ffe959a31d7bec3396..1c6b186e4d5fe02726c036c1c0fd92583be33808 100644 (file)
--- a/gdb/infrun.c
+++ b/gdb/infrun.c
@@ -5309,8 +5309,6 @@ Cannot fill $_exitsignal with the correct signal number.\n"));
       if (!ptid_equal (ecs->ptid, inferior_ptid))
        context_switch (ecs->ptid);
 
-      stop_pc = regcache_read_pc (get_thread_regcache (ecs->ptid));
-
       /* Do whatever is necessary to the parent branch of the vfork.  */
       handle_vfork_child_exec_or_exit (1);
 
@@ -5319,6 +5317,8 @@ Cannot fill $_exitsignal with the correct signal number.\n"));
          stop.  */
       follow_exec (inferior_ptid, ecs->ws.value.execd_pathname);
 
+      stop_pc = regcache_read_pc (get_thread_regcache (ecs->ptid));
+
       /* In follow_exec we may have deleted the original thread and
         created a new one.  Make sure that the event thread is the
         execd thread for that case (this is a nop otherwise).  */