[patch] Fix inferior execl of new PIE x86_64

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

Hi,

gcc -o 1 1.c -Wall -g -fPIE -pie; gdb -nx ./1 -ex 'b main' -ex r -ex c 

Starting program: .../gdb/1 
Breakpoint 1, main (argc=1, argv=0x7fffffffdff8) at 1.c:7
7	  setbuf (stdout, NULL);
Continuing.
re-exec
process 28056 is executing new program: .../gdb/1
Error in re-setting breakpoint 1: Cannot access memory at address 0x80c
exit
Program exited normally.
(gdb) _

while it should be:

re-exec
process 28095 is executing new program: .../gdb/1
Breakpoint 1, main (argc=2, argv=0x7fffffffe008) at 1.c:7
7	  setbuf (stdout, NULL);
(gdb) _

The error comes from:

throw_error <- memory_error <- read_memory <- read_memory_unsigned_integer <-
amd64_analyze_prologue <- amd64_skip_prologue <- gdbarch_skip_prologue <-
skip_prologue_sal <- find_function_start_sal <- symbol_found <- decode_variable
<- decode_line_1 <- breakpoint_re_set_one <- catch_errors <- breakpoint_re_set
<- clear_symtab_users <- new_symfile_objfile <-
symbol_file_add_with_addrs_or_offsets <- symbol_file_add_from_bfd <-
symbol_file_add <- symbol_file_add_main_1 <- symbol_file_add_main <-
follow_exec


I understand this hack is not nice, the correct way would be to unify more
follow_exec with post_create_inferior.  But I could break it for non-GNU/Linux
targets a lot.

No regressions on {x86_64,x86_64-m32,i686}-fedora14snapshot-linux-gnu.


Thanks,
Jan


for the demo above:
------------------------------------------------------------------------------
#include <unistd.h>
#include <assert.h>
#include <stdio.h>
int
main (int argc, char **argv)
{
  setbuf (stdout, NULL);
  if (argc == 1)
    {
      puts ("re-exec");
      execl ("/proc/self/exe", argv[0], "foo", NULL);
      assert (0);
    }
  puts ("exit");
  return 0;
}
------------------------------------------------------------------------------


gdb/
2010-09-30  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.

gdb/testsuite/
2010-09-30  Jan Kratochvil  <jan.kratochvil@redhat.com>

	* gdb.base/pie-execl.exp: New file.
	* gdb.base/pie-execl.c: New file.

--- a/gdb/infrun.c
+++ b/gdb/infrun.c
@@ -835,8 +835,15 @@ follow_exec (ptid_t pid, char *execd_pathname)
   /* 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 @@ follow_exec (ptid_t pid, char *execd_pathname)
 
   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...) */
--- a/gdb/m32r-rom.c
+++ b/gdb/m32r-rom.c
@@ -188,7 +188,7 @@ m32r_load (char *filename, int from_tty)
      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 @@ m32r_upload_command (char *args, int from_tty)
      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.  */
--- a/gdb/objfiles.c
+++ b/gdb/objfiles.c
@@ -692,7 +692,7 @@ free_all_objfiles (void)
   {
     free_objfile (objfile);
   }
-  clear_symtab_users ();
+  clear_symtab_users (0);
 }
 
 /* A helper function for objfile_relocate1 that relocates a single
--- a/gdb/remote-m32r-sdi.c
+++ b/gdb/remote-m32r-sdi.c
@@ -1377,7 +1377,7 @@ m32r_load (char *args, int from_tty)
      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)
     {
--- a/gdb/solib-som.c
+++ b/gdb/solib-som.c
@@ -354,7 +354,7 @@ keep_going:
   /* 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
--- a/gdb/symfile.c
+++ b/gdb/symfile.c
@@ -1035,7 +1035,7 @@ syms_from_objfile (struct objfile *objfile,
 
 /* 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)
@@ -1048,7 +1048,7 @@ new_symfile_objfile (struct objfile *objfile, int add_flags)
       /* 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)
     {
@@ -2527,7 +2527,7 @@ reread_symbols (void)
       /* 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 ();
@@ -2745,10 +2745,10 @@ allocate_symtab (char *filename, struct objfile *objfile)
 
 
 /* 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.  */
@@ -2758,7 +2758,8 @@ clear_symtab_users (void)
   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);
@@ -2777,7 +2778,7 @@ clear_symtab_users (void)
 static void
 clear_symtab_users_cleanup (void *ignore)
 {
-  clear_symtab_users ();
+  clear_symtab_users (0);
 }
 
 /* OVERLAYS:
--- a/gdb/symtab.h
+++ b/gdb/symtab.h
@@ -1186,7 +1186,7 @@ extern void skip_prologue_sal (struct symtab_and_line *);
 
 /* 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 *);
 
--- /dev/null
+++ b/gdb/testsuite/gdb.base/pie-execl.c
@@ -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;
+}
--- /dev/null
+++ b/gdb/testsuite/gdb.base/pie-execl.exp
@@ -0,0 +1,94 @@
+# 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
+}
+
+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
+}