[review] Fix backtrace of prelinked libc with separate debuginfo

[review] Fix backtrace of prelinked libc with separate debuginfo

[Jan Kratochvil]

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Hi,

currently (on Fedora Core 6) after installation of /usr/lib/debug separate
debuginfo files the backtraces no longer display some libc functions:

#5  <signal handler called>
#6  0x00c98402 in __kernel_vsyscall ()
#7  0x0077ebc6 in ?? () from /lib/i686/nosegneg/libc.so.6
#8  0x08048444 in main () at doublesym.c:15

while after `rm -rf /usr/lib/debug':

#5  <signal handler called>
#6  0x0087b402 in __kernel_vsyscall ()
#7  0x0077ebc6 in __pause_nocancel () from /lib/i686/nosegneg/libc.so.6
#8  0x08048444 in main () at doublesym.c:15

It is (I believe) due to the fact the system libc gets prelinked to some
address but the separate debuginfo file is not updated for the prelinked
address.  `matching_bfd_sections' will fail to match afterwards.

Not sure if the testcase properly fails on all systems, it works for me with
the prelinking in effect.


Regards,
Jan

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2006-10-29  Jan Kratochvil  <jan.kratochvil@redhat.com>

	* gdb/symtab.c (matching_bfd_sections): Fix VMA matching for objects
	loaded at a different address than stored on the disk.

2006-10-29  Jan Kratochvil  <jan.kratochvil@redhat.com>

	* gdb.base/relativedebug.c, gdb.base/relativedebug.exp: New file, 
	resolving of PC in libc pause(3) (with possibly different on-disk VMA).


Index: gdb/symtab.c
===================================================================
--- gdb/symtab.c	17 Oct 2006 20:17:44 -0000	1.148
+++ gdb/symtab.c	29 Oct 2006 22:29:21 -0000
@@ -739,8 +739,11 @@ matching_bfd_sections (asection *first, 
   if (bfd_get_section_size (first) != bfd_get_section_size (second))
     return 0;
 
+  /* In-memory addresses may start at a different offset, relativize them.  */
   if (bfd_get_section_vma (first->owner, first)
-      != bfd_get_section_vma (second->owner, second))
+      - bfd_get_start_address (first->owner)
+      != bfd_get_section_vma (second->owner, second)
+	 - bfd_get_start_address (second->owner))
     return 0;
 
   if (bfd_get_section_name (first->owner, first) == NULL
Index: gdb/testsuite/gdb.base/relativedebug.c
===================================================================
--- /dev/null	1 Jan 1970 00:00:00 -0000
+++ gdb/testsuite/gdb.base/relativedebug.c	29 Oct 2006 22:29:21 -0000
@@ -0,0 +1,37 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2006 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 2 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, write to the Free Software
+   Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
+   02111-1307, USA.  */
+
+#include <unistd.h>
+#include <stdlib.h>
+#include <signal.h>
+
+
+static void handler (int signo)
+{
+	abort ();
+}
+
+int main (void)
+{
+	signal (SIGALRM, handler);
+	alarm (1);
+	pause ();
+	pause ();
+	return 0;
+}
Index: gdb/testsuite/gdb.base/relativedebug.exp
===================================================================
--- /dev/null	1 Jan 1970 00:00:00 -0000
+++ gdb/testsuite/gdb.base/relativedebug.exp	29 Oct 2006 22:29:21 -0000
@@ -0,0 +1,68 @@
+# Copyright 2006 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 2 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, write to the Free Software
+# Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.  
+
+if $tracelevel then {
+    strace $tracelevel
+}
+
+set testfile relativedebug
+set srcfile ${testfile}.c
+set binfile ${objdir}/${subdir}/${testfile}
+if  { [gdb_compile "${srcdir}/${subdir}/${srcfile}" "${binfile}" executable {debug}] != "" } {
+    untested "Couldn't compile test program"
+    return -1
+}
+
+# Get things started.
+
+gdb_exit
+gdb_start
+gdb_reinitialize_dir $srcdir/$subdir
+gdb_load ${binfile}
+
+# pause () -> SIGALRM -> handler () -> abort ()
+
+gdb_test "run" \
+         ".*Program received signal SIGABRT, Aborted..*" \
+         "run"
+
+# incorrect (#6):
+# (gdb) bt
+# #0  0x00325402 in __kernel_vsyscall ()
+# #1  0x00718f20 in *__GI_raise (sig=6) at ../nptl/sysdeps/unix/sysv/linux/raise.c:64
+# #2  0x0071a801 in *__GI_abort () at abort.c:88
+# #3  0x0804841f in handler (signo=14) at ./gdb.base/relativedebug.c:27
+# #4  <signal handler called>
+# #5  0x00325402 in __kernel_vsyscall ()
+# #6  0x0077ebc6 in ?? () from /lib/i686/nosegneg/libc.so.6
+# #7  0x08048455 in main () at ./gdb.base/relativedebug.c:34
+# (gdb)
+
+# correct (#6):
+# (gdb) bt
+# #0  0x00b33402 in __kernel_vsyscall ()
+# #1  0x00718f20 in *__GI_raise (sig=6) at ../nptl/sysdeps/unix/sysv/linux/raise.c:64
+# #2  0x0071a801 in *__GI_abort () at abort.c:88
+# #3  0x0804841f in handler (signo=14) at ./gdb.base/relativedebug.c:27
+# #4  <signal handler called>
+# #5  0x00b33402 in __kernel_vsyscall ()
+# #6  0x0077ebc6 in __pause_nocancel () from /lib/i686/nosegneg/libc.so.6
+# #7  0x08048455 in main () at ./gdb.base/relativedebug.c:34
+# (gdb)
+
+gdb_test "bt" \
+         ".*\[^a-zA-Z\]pause\[^a-zA-Z\].*" \
+         "pause(3) seen there"

Re: [review] Fix backtrace of prelinked libc with separate debuginfo

[Daniel Jacobowitz]

On Sun, Oct 29, 2006 at 11:39:12PM +0100, Jan Kratochvil wrote:
> It is (I believe) due to the fact the system libc gets prelinked to some
> address but the separate debuginfo file is not updated for the prelinked
> address.  `matching_bfd_sections' will fail to match afterwards.
> 
> Not sure if the testcase properly fails on all systems, it works for me with
> the prelinking in effect.

Right.  It won't fail on Debian even with prelinking - I think this is
because Debian uses binutils' objcopy program, which puts the stripped
symbols in the debug file, but eu-strip leaves them only in the
original file.  Which seems pretty strange but that's what it does.

> 2006-10-29  Jan Kratochvil  <jan.kratochvil@redhat.com>
> 
> 	* gdb/symtab.c (matching_bfd_sections): Fix VMA matching for objects
> 	loaded at a different address than stored on the disk.
> 
> 2006-10-29  Jan Kratochvil  <jan.kratochvil@redhat.com>
> 
> 	* gdb.base/relativedebug.c, gdb.base/relativedebug.exp: New file, 
> 	resolving of PC in libc pause(3) (with possibly different on-disk VMA).

I updated the test case to work with remote targets and then checked
this in.

-- 
Daniel Jacobowitz
CodeSourcery

2007-01-09  Jan Kratochvil  <jan.kratochvil@redhat.com>

	* symtab.c (matching_bfd_sections): Fix VMA matching for
	prelinked objects.

2007-01-09  Jan Kratochvil  <jan.kratochvil@redhat.com>

	* gdb.base/relativedebug.c, gdb.base/relativedebug.exp: New files.

Index: symtab.c
===================================================================
RCS file: /cvs/src/src/gdb/symtab.c,v
retrieving revision 1.151
diff -u -p -r1.151 symtab.c
--- symtab.c	9 Jan 2007 17:58:59 -0000	1.151
+++ symtab.c	9 Jan 2007 22:39:14 -0000
@@ -739,8 +739,11 @@ matching_bfd_sections (asection *first, 
   if (bfd_get_section_size (first) != bfd_get_section_size (second))
     return 0;
 
+  /* In-memory addresses may start at a different offset, relativize them.  */
   if (bfd_get_section_vma (first->owner, first)
-      != bfd_get_section_vma (second->owner, second))
+      - bfd_get_start_address (first->owner)
+      != bfd_get_section_vma (second->owner, second)
+	 - bfd_get_start_address (second->owner))
     return 0;
 
   if (bfd_get_section_name (first->owner, first) == NULL
Index: testsuite/gdb.base/relativedebug.c
===================================================================
RCS file: testsuite/gdb.base/relativedebug.c
diff -N testsuite/gdb.base/relativedebug.c
--- /dev/null	1 Jan 1970 00:00:00 -0000
+++ testsuite/gdb.base/relativedebug.c	9 Jan 2007 22:39:14 -0000
@@ -0,0 +1,37 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2007 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 2 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, write to the Free Software
+   Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
+   02111-1307, USA.  */
+
+#include <unistd.h>
+#include <stdlib.h>
+#include <signal.h>
+
+
+static void handler (int signo)
+{
+	abort ();
+}
+
+int main (void)
+{
+	signal (SIGALRM, handler);
+	alarm (1);
+	pause ();
+	pause ();
+	return 0;
+}
Index: testsuite/gdb.base/relativedebug.exp
===================================================================
RCS file: testsuite/gdb.base/relativedebug.exp
diff -N testsuite/gdb.base/relativedebug.exp
--- /dev/null	1 Jan 1970 00:00:00 -0000
+++ testsuite/gdb.base/relativedebug.exp	9 Jan 2007 22:39:14 -0000
@@ -0,0 +1,71 @@
+# Copyright 2007 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 2 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, write to the Free Software
+# Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.  
+
+if $tracelevel then {
+    strace $tracelevel
+}
+
+set testfile relativedebug
+set srcfile ${testfile}.c
+set binfile ${objdir}/${subdir}/${testfile}
+if  { [gdb_compile "${srcdir}/${subdir}/${srcfile}" "${binfile}" executable {debug}] != "" } {
+    untested "Couldn't compile test program"
+    return -1
+}
+
+# Get things started.
+
+gdb_exit
+gdb_start
+gdb_reinitialize_dir $srcdir/$subdir
+gdb_load ${binfile}
+
+runto_main
+
+# pause () -> SIGALRM -> handler () -> abort ()
+gdb_test "continue" "Program received signal SIGABRT.*"
+
+# Backtracing through pause broke if glibc has been prelinked,
+# because the separate debug files in /usr/lib/debug had different
+# base addresses.
+
+# incorrect (#6):
+# (gdb) bt
+# #0  0x00325402 in __kernel_vsyscall ()
+# #1  0x00718f20 in *__GI_raise (sig=6) at ../nptl/sysdeps/unix/sysv/linux/raise.c:64
+# #2  0x0071a801 in *__GI_abort () at abort.c:88
+# #3  0x0804841f in handler (signo=14) at ./gdb.base/relativedebug.c:27
+# #4  <signal handler called>
+# #5  0x00325402 in __kernel_vsyscall ()
+# #6  0x0077ebc6 in ?? () from /lib/i686/nosegneg/libc.so.6
+# #7  0x08048455 in main () at ./gdb.base/relativedebug.c:34
+# (gdb)
+
+# correct (#6):
+# (gdb) bt
+# #0  0x00b33402 in __kernel_vsyscall ()
+# #1  0x00718f20 in *__GI_raise (sig=6) at ../nptl/sysdeps/unix/sysv/linux/raise.c:64
+# #2  0x0071a801 in *__GI_abort () at abort.c:88
+# #3  0x0804841f in handler (signo=14) at ./gdb.base/relativedebug.c:27
+# #4  <signal handler called>
+# #5  0x00b33402 in __kernel_vsyscall ()
+# #6  0x0077ebc6 in __pause_nocancel () from /lib/i686/nosegneg/libc.so.6
+# #7  0x08048455 in main () at ./gdb.base/relativedebug.c:34
+# (gdb)
+
+gdb_test "bt" \
+         ".*\[^a-zA-Z\]pause\[^a-zA-Z\].*" \
+         "pause found in backtrace"

Re: [review] Fix backtrace of prelinked libc with separate debuginfo

[Jan Kratochvil]

On Tue, 09 Jan 2007 23:43:23 +0100, Daniel Jacobowitz wrote:
> On Sun, Oct 29, 2006 at 11:39:12PM +0100, Jan Kratochvil wrote:
> > It is (I believe) due to the fact the system libc gets prelinked to some
> > address but the separate debuginfo file is not updated for the prelinked
> > address.  `matching_bfd_sections' will fail to match afterwards.
> > 
> > Not sure if the testcase properly fails on all systems, it works for me with
> > the prelinking in effect.
> 
> Right.  It won't fail on Debian even with prelinking

I was trying to figure it out but there are too many combinations and without
the system available... While my patch was for matching_bfd_sections() (not
present in gdb-6.5 and therefore neither in debian-unstable) I imported
matching_bfd_sections() specifically to fix this bug before as it was easier
than without the matching_bfd_sections() patch.


> - I think this is
> because Debian uses binutils' objcopy program, which puts the stripped
> symbols in the debug file, but eu-strip leaves them only in the
> original file.  Which seems pretty strange but that's what it does.

The libbfd backward compatibility was recently restored by elfutils.
Currently a partial symtab copy is being made:

* Wed Oct 11 2006 Roland McGrath <roland@redhat.com> - 0.124-1
- eu-strip -f: copy symtab into debuginfo file when relocs use it

...
> I updated the test case to work with remote targets and then checked
> this in.

Thanks.


Regards,
Jan

Re: [review] Fix backtrace of prelinked libc with separate debuginfo

[Daniel Jacobowitz]

On Thu, Jan 11, 2007 at 11:17:25PM +0100, Jan Kratochvil wrote:
> > - I think this is
> > because Debian uses binutils' objcopy program, which puts the stripped
> > symbols in the debug file, but eu-strip leaves them only in the
> > original file.  Which seems pretty strange but that's what it does.
> 
> The libbfd backward compatibility was recently restored by elfutils.
> Currently a partial symtab copy is being made:
> 
> * Wed Oct 11 2006 Roland McGrath <roland@redhat.com> - 0.124-1
> - eu-strip -f: copy symtab into debuginfo file when relocs use it

Thanks - that's good to know.

-- 
Daniel Jacobowitz
CodeSourcery