[PATCH] PR gdb/14306 - GDB doesn't work when execing different format

[Pedro Alves <palves at redhat dot com>]

When handling an exec, we load the new image as new exec_bfd, which
updates the current gdbarch to reflect the new executable.  But, we
fail to refetch a new target description from the target, ending up
with e.g.:

(gdb) c
Continuing.
process 21057 is executing new program: /usr/bin/ls
warning: Selected architecture i386:x86-64 is not compatible with reported
target architecture i386
Architecture of file not recognized.
(gdb)

In this case, /usr/bin/ls is 64-bit, while the pre-exec program was
32-bit.  We tried to match the old 32-bit target description with the
new 64-bit executable, which doesn't work.

This fixes it.  Tested on x86_64 Fedora 17, and applied.

gdb/
2012-11-09  Pedro Alves  <palves@redhat.com>

	PR gdb/14306

	* infrun.c: Include target-descriptions.h.
	(follow_exec): Fetch new target description.

gdb/testsuite/
2012-11-09  Pedro Alves  <palves@redhat.com>

	PR gdb/14306

	* gdb.multi/multi-arch-exec.c: New file.
	* gdb.multi/multi-arch-exec.exp: New file.
---
 gdb/infrun.c                                |   19 ++++++++
 gdb/testsuite/gdb.multi/multi-arch-exec.c   |   29 ++++++++++++
 gdb/testsuite/gdb.multi/multi-arch-exec.exp |   64 +++++++++++++++++++++++++++
 3 files changed, 112 insertions(+)
 create mode 100644 gdb/testsuite/gdb.multi/multi-arch-exec.c
 create mode 100644 gdb/testsuite/gdb.multi/multi-arch-exec.exp

diff --git a/gdb/infrun.c b/gdb/infrun.c
index 3d6eccd..4efc2af 100644
--- a/gdb/infrun.c
+++ b/gdb/infrun.c
@@ -58,6 +58,7 @@
 #include "probe.h"
 #include "objfiles.h"
 #include "completer.h"
+#include "target-descriptions.h"
 
 /* Prototypes for local functions */
 
@@ -913,6 +914,16 @@ follow_exec (ptid_t pid, char *execd_pathname)
       set_current_inferior (inf);
       set_current_program_space (pspace);
     }
+  else
+    {
+      /* The old description may no longer be fit for the new image.
+	 E.g, a 64-bit process exec'ed a 32-bit process.  Clear the
+	 old description; we'll read a new one below.  No need to do
+	 this on "follow-exec-mode new", as the old inferior stays
+	 around (its description is later cleared/refetched on
+	 restart).  */
+      target_clear_description ();
+    }
 
   gdb_assert (current_program_space == inf->pspace);
 
@@ -932,6 +943,14 @@ follow_exec (ptid_t pid, char *execd_pathname)
   if ((inf->symfile_flags & SYMFILE_NO_READ) == 0)
     set_initial_language ();
 
+  /* If the target can specify a description, read it.  Must do this
+     after flipping to the new executable (because the target supplied
+     description must be compatible with the executable's
+     architecture, and the old executable may e.g., be 32-bit, while
+     the new one 64-bit), and before anything involving memory or
+     registers.  */
+  target_find_description ();
+
 #ifdef SOLIB_CREATE_INFERIOR_HOOK
   SOLIB_CREATE_INFERIOR_HOOK (PIDGET (inferior_ptid));
 #else
diff --git a/gdb/testsuite/gdb.multi/multi-arch-exec.c b/gdb/testsuite/gdb.multi/multi-arch-exec.c
new file mode 100644
index 0000000..3d1c240
--- /dev/null
+++ b/gdb/testsuite/gdb.multi/multi-arch-exec.c
@@ -0,0 +1,29 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2012 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#include <stdio.h>
+#include <unistd.h>
+
+int
+main ()
+{
+  execl ("gdb.multi/multi-arch-exec-hello",
+         "gdb.multi/multi-arch-exec-hello",
+         (char *) NULL);
+  perror ("execl failed");
+  exit (1);
+}
diff --git a/gdb/testsuite/gdb.multi/multi-arch-exec.exp b/gdb/testsuite/gdb.multi/multi-arch-exec.exp
new file mode 100644
index 0000000..785ca8d
--- /dev/null
+++ b/gdb/testsuite/gdb.multi/multi-arch-exec.exp
@@ -0,0 +1,64 @@
+# Copyright 2009-2012 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# Test multi-exec / multi-process features that work for all configurations,
+# even ones that cannot run multiple processes simultaneously.
+
+set testfile "multi-arch-exec"
+
+# The plain remote target can't do multiple inferiors.
+if [target_info exists use_gdb_stub] {
+    return
+}
+
+# Can't use standard_testfile, we want executables with specialized
+# names.
+set exec1 "multi-arch-exec"
+set srcfile1 multi-arch-exec.c
+set binfile1 [standard_output_file ${exec1}]
+
+set exec2 "multi-arch-exec-hello"
+set srcfile2 hello.c
+set binfile2 [standard_output_file ${exec2}]
+
+# Build two executables, one for each arch.
+
+if [istarget "s390*-*-*"] {
+    set march1 "-m64"
+    set march2 "-m31"
+} else {
+    set march1 "-m64"
+    set march2 "-m32"
+}
+
+if { [prepare_for_testing ${testfile}.exp ${exec1} "${srcfile1}" \
+	  [list debug nowarnings additional_flags=${march1}]] } {
+    return -1
+}
+
+if { [prepare_for_testing ${testfile}.exp ${exec2} "${srcfile2}" \
+	  [list debug nowarnings additional_flags=${march2}]] } {
+    return -1
+}
+
+clean_restart ${exec1}
+if ![runto_main] then {
+    fail "Couldn't run to main"
+    return -1
+}
+
+# Test that GDB updates the target description / arch successfuly
+# after the exec.
+gdb_test "continue" "Breakpoint 1, main.*" "continue across exec that changes architecture"