Re: [patch] Fix inferior execl of new PIE x86_64

[Jan Kratochvil <jan dot kratochvil at redhat dot com>]

On Sat, 16 Oct 2010 01:20:45 +0200, Pedro Alves wrote:
> Hmm.  I'm looking at clear_symtab_users, and noticing that varobj_invalidate
> also appears to recreate varobj's, thus, it ends up using the unrelocated
> symbols, and thus may manage to not trigger an exception and end up with
> varobj's with the wrong values.  (If an exception is triggered, say a memory
> error, it appears that is caught and swallowed, and the varobjs ends
> up with no value.)

OK... I agree there is a problem.

time T+0: FE did -var-update, stopped.
time T+1: inferior did exec, GDB did follow-exec.
time T+2: FE did -var-update, stopped.

IMO the goal is to report at time T+2 the changes of types/values between T+0
and T+2.  Even if we would call varobj_invalidate after relocations from
follow_exec still MI would report only changes between T+1 and T+2.  Changes
between T+0 and T+1 would still get lost.

There is IMO already a problem in the defined API of varobj_invalidate.  The
invalidation has been made more fine grained by (never checked-in):
	[patch 8/8] Types GC [varobj]
	http://sourceware.org/ml/gdb-patches/2009-05/msg00551.html

(Part of the types garbage collector as a preprequisite for VLA (Variable
Length Arrays, for var[variable] and/or Fortran.)


Therefore currently postponing that part of the problem till the resubmit of
GC/VLA.


> Your patch looks like an improvement already, so it is okay as is with me.

Checked-in.


> Please make the test be skipped against remote targets though, since
> there's no support for following execs in the remote protocol.

if [is_remote target] {


Thanks,
Jan


http://sourceware.org/ml/gdb-cvs/2010-10/msg00101.html

--- src/gdb/ChangeLog	2010/10/17 08:43:45	1.12265
+++ src/gdb/ChangeLog	2010/10/17 17:45:16	1.12266
@@ -1,5 +1,23 @@
 2010-10-17  Jan Kratochvil  <jan.kratochvil@redhat.com>
 
+	* infrun.c (follow_exec): Replace symbol_file_add_main by
+	symbol_file_add with SYMFILE_DEFER_BP_RESET, set_initial_language and
+	breakpoint_re_set.
+	* m32r-rom.c (m32r_load, m32r_upload_command): Use parameter 0 for
+	clear_symtab_users.
+	* objfiles.c (free_all_objfiles): Likewise.
+	* remote-m32r-sdi.c (m32r_load): Likewise.
+	* solib-som.c (som_solib_create_inferior_hook): Likewise.
+	* symfile.c (new_symfile_objfile): New comment for add_flags.  Call
+	clear_symtab_users with ADD_FLAGS.
+	(reread_symbols): Use parameter 0 for clear_symtab_users.
+	(clear_symtab_users): New parameter add_flags.  Do not call
+	breakpoint_re_set if SYMFILE_DEFER_BP_RESET.
+	(clear_symtab_users_cleanup): Use parameter 0 for clear_symtab_users.
+	* symtab.h (clear_symtab_users): New parameter add_flags.
+
+2010-10-17  Jan Kratochvil  <jan.kratochvil@redhat.com>
+
 	Fix GCC false warning.
 	* varobj.c (value_get_print_value) <str_addr>: Initialize it.
 
--- src/gdb/testsuite/ChangeLog	2010/10/15 17:48:47	1.2481
+++ src/gdb/testsuite/ChangeLog	2010/10/17 17:45:17	1.2482
@@ -1,3 +1,8 @@
+2010-10-17  Jan Kratochvil  <jan.kratochvil@redhat.com>
+
+	* gdb.base/pie-execl.exp: New file.
+	* gdb.base/pie-execl.c: New file.
+
 2010-10-13  Doug Evans  <dje@google.com>
 	    Jan Kratochvil  <jan.kratochvil@redhat.com>
 
--- src/gdb/infrun.c	2010/09/24 18:35:27	1.451
+++ src/gdb/infrun.c	2010/10/17 17:45:16	1.452
@@ -835,8 +835,15 @@
   /* That a.out is now the one to use. */
   exec_file_attach (execd_pathname, 0);
 
-  /* Load the main file's symbols.  */
-  symbol_file_add_main (execd_pathname, 0);
+  /* SYMFILE_DEFER_BP_RESET is used as the proper displacement for PIE
+     (Position Independent Executable) main symbol file will get applied by
+     solib_create_inferior_hook below.  breakpoint_re_set would fail to insert
+     the breakpoints with the zero displacement.  */
+
+  symbol_file_add (execd_pathname, SYMFILE_MAINLINE | SYMFILE_DEFER_BP_RESET,
+		   NULL, 0);
+
+  set_initial_language ();
 
 #ifdef SOLIB_CREATE_INFERIOR_HOOK
   SOLIB_CREATE_INFERIOR_HOOK (PIDGET (inferior_ptid));
@@ -846,6 +853,8 @@
 
   jit_inferior_created_hook ();
 
+  breakpoint_re_set ();
+
   /* Reinsert all breakpoints.  (Those which were symbolic have
      been reset to the proper address in the new a.out, thanks
      to symbol_file_command...) */
--- src/gdb/m32r-rom.c	2010/09/14 08:01:12	1.41
+++ src/gdb/m32r-rom.c	2010/10/17 17:45:16	1.42
@@ -188,7 +188,7 @@
      the stack may not be valid, and things would get horribly
      confused... */
 
-  clear_symtab_users ();
+  clear_symtab_users (0);
 }
 
 static void
@@ -551,7 +551,7 @@
      the stack may not be valid, and things would get horribly
      confused... */
 
-  clear_symtab_users ();
+  clear_symtab_users (0);
 }
 
 /* Provide a prototype to silence -Wmissing-prototypes.  */
--- src/gdb/objfiles.c	2010/09/22 20:00:53	1.122
+++ src/gdb/objfiles.c	2010/10/17 17:45:16	1.123
@@ -692,7 +692,7 @@
   {
     free_objfile (objfile);
   }
-  clear_symtab_users ();
+  clear_symtab_users (0);
 }
 
 /* A helper function for objfile_relocate1 that relocates a single
--- src/gdb/remote-m32r-sdi.c	2010/09/14 08:01:12	1.53
+++ src/gdb/remote-m32r-sdi.c	2010/10/17 17:45:16	1.54
@@ -1377,7 +1377,7 @@
      might be to call normal_stop, except that the stack may not be valid,
      and things would get horribly confused... */
 
-  clear_symtab_users ();
+  clear_symtab_users (0);
 
   if (!nostart)
     {
--- src/gdb/solib-som.c	2010/05/16 23:49:58	1.29
+++ src/gdb/solib-som.c	2010/10/17 17:45:16	1.30
@@ -354,7 +354,7 @@
   /* Make the breakpoint at "_start" a shared library event breakpoint.  */
   create_solib_event_breakpoint (target_gdbarch, anaddr);
 
-  clear_symtab_users ();
+  clear_symtab_users (0);
 }
 
 static void
--- src/gdb/symfile.c	2010/10/01 20:26:11	1.297
+++ src/gdb/symfile.c	2010/10/17 17:45:16	1.298
@@ -1038,7 +1038,7 @@
 
 /* Perform required actions after either reading in the initial
    symbols for a new objfile, or mapping in the symbols from a reusable
-   objfile. */
+   objfile.  ADD_FLAGS is a bitmask of enum symfile_add_flags.  */
 
 void
 new_symfile_objfile (struct objfile *objfile, int add_flags)
@@ -1051,7 +1051,7 @@
       /* OK, make it the "real" symbol file.  */
       symfile_objfile = objfile;
 
-      clear_symtab_users ();
+      clear_symtab_users (add_flags);
     }
   else if ((add_flags & SYMFILE_DEFER_BP_RESET) == 0)
     {
@@ -2530,7 +2530,7 @@
       /* Notify objfiles that we've modified objfile sections.  */
       objfiles_changed ();
 
-      clear_symtab_users ();
+      clear_symtab_users (0);
       /* At least one objfile has changed, so we can consider that
          the executable we're debugging has changed too.  */
       observer_notify_executable_changed ();
@@ -2748,10 +2748,10 @@
 
 
 /* Reset all data structures in gdb which may contain references to symbol
-   table data.  */
+   table data.  ADD_FLAGS is a bitmask of enum symfile_add_flags.  */
 
 void
-clear_symtab_users (void)
+clear_symtab_users (int add_flags)
 {
   /* Someday, we should do better than this, by only blowing away
      the things that really need to be blown.  */
@@ -2761,7 +2761,8 @@
   clear_current_source_symtab_and_line ();
 
   clear_displays ();
-  breakpoint_re_set ();
+  if ((add_flags & SYMFILE_DEFER_BP_RESET) == 0)
+    breakpoint_re_set ();
   set_default_breakpoint (0, NULL, 0, 0, 0);
   clear_pc_function_cache ();
   observer_notify_new_objfile (NULL);
@@ -2780,7 +2781,7 @@
 static void
 clear_symtab_users_cleanup (void *ignore)
 {
-  clear_symtab_users ();
+  clear_symtab_users (0);
 }
 
 /* OVERLAYS:
--- src/gdb/symtab.h	2010/09/08 17:17:42	1.163
+++ src/gdb/symtab.h	2010/10/17 17:45:16	1.164
@@ -1186,7 +1186,7 @@
 
 /* symfile.c */
 
-extern void clear_symtab_users (void);
+extern void clear_symtab_users (int add_flags);
 
 extern enum language deduce_language_from_filename (const char *);
 
--- src/gdb/testsuite/gdb.base/pie-execl.c
+++ src/gdb/testsuite/gdb.base/pie-execl.c	2010-10-17 17:45:47.138149000 +0000
@@ -0,0 +1,51 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2010 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>
+#include <assert.h>
+
+static void pie_execl_marker (void);
+
+int
+main (int argc, char **argv)
+{
+  setbuf (stdout, NULL);
+
+#if BIN == 1
+  if (argc == 2)
+    {
+      printf ("pie-execl: re-exec: %s\n", argv[1]);
+      execl (argv[1], argv[1], NULL);
+      assert (0);
+    }
+#endif
+
+  pie_execl_marker ();
+
+  return 0;
+}
+
+/* pie_execl_marker must be on a different address than in `pie-execl2.c'.  */
+
+volatile int v;
+
+static void
+pie_execl_marker (void)
+{
+  v = 1;
+}
--- src/gdb/testsuite/gdb.base/pie-execl.exp
+++ src/gdb/testsuite/gdb.base/pie-execl.exp	2010-10-17 17:45:47.456930000 +0000
@@ -0,0 +1,100 @@
+# Copyright 2010 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/>.
+
+# The problem was due to amd64_skip_prologue attempting to access inferior
+# memory before the PIE (Position Independent Executable) gets relocated.
+
+if ![istarget *-linux*] {
+    continue
+}
+
+# Remote protocol does not support follow-exec notifications.
+
+if [is_remote target] {
+    continue
+}
+
+set testfile "pie-execl"
+set srcfile ${testfile}.c
+set executable1 ${testfile}1
+set executable2 ${testfile}2
+set binfile1 ${objdir}/${subdir}/${executable1}
+set binfile2 ${objdir}/${subdir}/${executable2}
+
+# Use conditional compilation according to `BIN' as GDB remembers the source
+# file name of the breakpoint.
+
+set opts [list debug {additional_flags=-fPIE -pie}]
+if {[build_executable ${testfile}.exp $executable1 $srcfile [concat $opts {additional_flags=-DBIN=1}]] == ""
+    || [build_executable ${testfile}.exp $executable2 $srcfile [concat $opts {additional_flags=-DBIN=2}]] == ""} {
+    return -1
+}
+
+clean_restart ${executable1}
+
+gdb_test_no_output "set args ${binfile2}"
+
+if ![runto_main] {
+    return -1
+}
+
+# Do not stop on `main' after re-exec.
+delete_breakpoints
+
+gdb_breakpoint "pie_execl_marker"
+gdb_test "info breakpoints" ".*" ""
+
+set addr1 ""
+set test "pie_execl_marker address first"
+gdb_test_multiple "p/x &pie_execl_marker" $test {
+    -re " = (0x\[0-9a-f\]+)\r\n$gdb_prompt $" {
+	set addr1 $expect_out(1,string)
+	pass $test
+    }
+}
+verbose -log "addr1 is $addr1"
+
+set test "continue"
+gdb_test_multiple $test $test {
+    -re "Error in re-setting breakpoint" {
+	fail $test
+    }
+    -re "Cannot access memory" {
+	fail $test
+    }
+    -re "pie-execl: re-exec.*executing new program.*\r\nBreakpoint \[0-9\]+,\[^\r\n\]* pie_execl_marker .*\r\n$gdb_prompt $" {
+	pass $test
+    }
+}
+
+gdb_test "info breakpoints" ".*" ""
+
+set addr2 ""
+set test "pie_execl_marker address second"
+gdb_test_multiple "p/x &pie_execl_marker" $test {
+    -re " = (0x\[0-9a-f\]+)\r\n$gdb_prompt $" {
+	set addr2 $expect_out(1,string)
+	pass $test
+    }
+}
+verbose -log "addr2 is $addr2"
+
+# Ensure we cannot get a false PASS and the inferior has really changed.
+set test "pie_execl_marker address has changed"
+if [string equal $addr1 $addr2] {
+    fail $test
+} else {
+    pass $test
+}