[patch] Fix a crash when displaying variables from shared library.

Paul Pluzhnikov
2009-02-05T03:03:11Z

Greetings,

Consider this source:

/* main.c */
int main() { return foo(); }

/* foo.c; compile as a shared library */
int a_global;
int foo() { return ++a_global; }

If you set "display a_global", and re-run the program, GDB will
crash (gdb-6.7, 6.8, Head).

This is happening because display_chain expressions refer to
symbols, but solib symbols get freed and reloaded across inferior
restarts.

Attached patch adds a test case and fixes the problem.

Tested on x86_64-linux with no regressions.

OK to commit?

--
Paul Pluzhnikov

ChangeLog:

2009-02-04 Paul Pluzhnikov <ppluzhnikov@google.com>

* printcmd.c (do_one_display): Reparse exp_string.
(clear_dangling_display_expressions): New function.
(_initialize_printcmd): Add observer.
* solib.c (clear_solib): Add missing notification.

testsuite/ChangeLog:

2009-02-04 Paul Pluzhnikov <ppluzhnikov@google.com>

* solib-display.exp: New file.
* solib-display-main.c: New file.
* solib-display-lib.c: New file.

Index: printcmd.c
===================================================================
RCS file: /cvs/src/src/gdb/printcmd.c,v
retrieving revision 1.142
diff -u -p -u -r1.142 printcmd.c
--- printcmd.c 5 Feb 2009 00:13:43 -0000 1.142
+++ printcmd.c 5 Feb 2009 02:43:31 -0000
@@ -43,6 +43,7 @@
#include "disasm.h"
#include "dfp.h"
#include "valprint.h"
+#include "observer.h"

#ifdef TUI
#include "tui/tui.h" /* For tui_active et.al. */
@@ -1526,6 +1527,9 @@ do_one_display (struct display *d)
if (!within_current_scope)
return;

+ if (d->exp == NULL)
+ d->exp = parse_expression (d->exp_string);
+
current_display_number = d->number;

annotate_display_begin ();
@@ -1731,6 +1735,18 @@ disable_display_command (char *args, int
p++;
}
}
+
+static void
+clear_dangling_display_expressions (struct so_list *solist)
+{
+ struct display *d;
+
+ for (d = display_chain; d; d = d->next)
+ {
+ xfree (d->exp);
+ d->exp = NULL;
+ }
+}
\f

/* Print the value in stack frame FRAME of a variable specified by a
@@ -2367,6 +2383,8 @@ _initialize_printcmd (void)

current_display_number = -1;

+ observer_attach_solib_unloaded (clear_dangling_display_expressions);
+
add_info ("address", address_info,
_("Describe where symbol SYM is stored."));

Index: solib.c
===================================================================
RCS file: /cvs/src/src/gdb/solib.c,v
retrieving revision 1.109
diff -u -p -u -r1.109 solib.c
--- solib.c 15 Jan 2009 16:35:22 -0000 1.109
+++ solib.c 5 Feb 2009 02:43:31 -0000
@@ -908,6 +908,7 @@ clear_solib (void)
{
struct so_list *so = so_list_head;
so_list_head = so->next;
+ observer_notify_solib_unloaded (so);
if (so->abfd)
remove_target_sections (so->abfd);
free_so (so);
Index: testsuite/gdb.base/solib-display-lib.c
===================================================================
RCS file: testsuite/gdb.base/solib-display-lib.c
diff -N testsuite/gdb.base/solib-display-lib.c
--- /dev/null 1 Jan 1970 00:00:00 -0000
+++ testsuite/gdb.base/solib-display-lib.c 5 Feb 2009 02:43:31 -0000
@@ -0,0 +1,19 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+ Copyright 2009 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/>. */
+
+int a_global;
+int foo () { return ++a_global; }
Index: testsuite/gdb.base/solib-display-main.c
===================================================================
RCS file: testsuite/gdb.base/solib-display-main.c
diff -N testsuite/gdb.base/solib-display-main.c
--- /dev/null 1 Jan 1970 00:00:00 -0000
+++ testsuite/gdb.base/solib-display-main.c 5 Feb 2009 02:43:31 -0000
@@ -0,0 +1,23 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+ Copyright 2009 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/>. */
+
+extern int foo ();
+
+int main ()
+{
+ return foo ();
+}
Index: testsuite/gdb.base/solib-display.exp
===================================================================
RCS file: testsuite/gdb.base/solib-display.exp
diff -N testsuite/gdb.base/solib-display.exp
--- /dev/null 1 Jan 1970 00:00:00 -0000
+++ testsuite/gdb.base/solib-display.exp 5 Feb 2009 02:43:31 -0000
@@ -0,0 +1,61 @@
+# Copyright 2009 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/>.
+#
+# Contributed by Paul Pluzhnikov <ppluzhnikov@google.com>
+#
+
+if {[skip_shlib_tests]} {
+ return 0
+}
+
+# Library file.
+set libname "solib-display-lib"
+set srcfile_lib ${srcdir}/${subdir}/${libname}.c
+set binfile_lib ${objdir}/${subdir}/${libname}.so
+set lib_flags [list debug ldflags=-Wl,-Bsymbolic]
+# Binary file.
+set testfile "solib-display-main"
+set srcfile ${srcdir}/${subdir}/${testfile}.c
+set binfile ${objdir}/${subdir}/${testfile}
+set bin_flags [list debug shlib=${binfile_lib}]
+
+if [get_compiler_info ${binfile}] {
+ return -1
+}
+
+if { [gdb_compile_shlib ${srcfile_lib} ${binfile_lib} $lib_flags] != ""
+ || [gdb_compile ${srcfile} ${binfile} executable $bin_flags] != "" } {
+ untested "Could not compile $binfile_lib or $binfile."
+ return -1
+}
+
+gdb_exit
+gdb_start
+gdb_reinitialize_dir $srcdir/$subdir
+gdb_load ${binfile}
+
+if ![runto_main] then {
+ fail "Can't run to main"
+ return 0
+}
+
+gdb_test "display a_global"
+gdb_test "continue"
+gdb_test "run" "1: a_global = 0"
+
+gdb_exit
+
+return 0
+
+