[binutils-gdb/gdb-8.0-branch] Read stop_pc after updating the gdbarch when exec'ing

[Simon Marchi <simark at sourceware dot org>]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=61bffb81d5ffdb7c6005b7b7fb6cfd8e9e6b19ce

commit 61bffb81d5ffdb7c6005b7b7fb6cfd8e9e6b19ce
Author: Simon Marchi <simon.marchi@ericsson.com>
Date:   Tue Sep 5 16:45:10 2017 +0200

    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:
---
 gdb/ChangeLog | 5 +++++
 gdb/infrun.c  | 4 ++--
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 25310e7..81b7960 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,5 +1,10 @@
 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.
 
 2017-09-01  Jan Kratochvil  <jan.kratochvil@redhat.com>
diff --git a/gdb/infrun.c b/gdb/infrun.c
index 8a67633..fd62a9b 100644
--- a/gdb/infrun.c
+++ b/gdb/infrun.c
@@ -5326,8 +5326,6 @@ 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);
 
@@ -5336,6 +5334,8 @@ 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).  */