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Re: [RFA/symtab] Handle weak functions as global
- From: Daniel Jacobowitz <drow at false dot org>
- To: gdb-patches at sources dot redhat dot com
- Date: Fri, 1 Dec 2006 13:15:08 -0500
- Subject: Re: [RFA/symtab] Handle weak functions as global
- References: <20041101173014.GA20449@nevyn.them.org>
I was reminded about this patch, two years old now, earlier in the
week. I've updated it and applied it; patch and testcase below.
On Mon, Nov 01, 2004 at 12:30:15PM -0500, Daniel Jacobowitz wrote:
> This patch is a one liner, but requires a bit of explanation. If you have a
> version of glibc available with debugging symbols (in both ld.so and
> libc.so), you can see the problem like this:
>
> - Compile a program which calls open ().
> - Run to main.
> - Set a breakpoint on open.
> - Continue - the breakpoint will not be hit.
>
> [Separate debug files will show the bug if you point GDB at the right
> directory; on Debian this is /usr/lib/debug, not sure where it is on RH
> systems.]
>
> What happens, in my setup at least, is that gdb searches first the
> executable, then libc.so.6, then ld.so for "open". It either finds a
> trampoline in the executable or nothing at all (depending on your version of
> binutils). Then, it finds open in libc.so.6, which has type mst_file_text.
> Then it finds open in ld.so, which also has a symbol named open, which also
> has type mst_file_text. We did not find any mst_text symbol, so we settle
> for returning the most recent mst_file_text symbol - which is the wrong one.
>
> There's two strange things here. The first is that we return the second
> file symbol instead of the first; it doesn't much matter, since we'll be
> wrong half the time anyway. The second is that the symbol in libc.so is
> marked as mst_file_text. This turned out to be because BSF_WEAK handling
> was added to elfread for non-code symbols, but not for code symbols; and
> open is a weak entry point to libc.so.6 for historical reasons. If we treat
> it as global, paralleling the non-code symbol handling, then GDB will
> resolve breakpoints on "open" reliably to libc.so.6 (assuming no other
> shared library defines it). This gives the debugger much better chances of
> finding the right symbol - any situation more complicated would require
> setting breakpoints at all functions named "open", which is a To-Do-Later
> issue.
--
Daniel Jacobowitz
CodeSourcery
2006-12-01 Daniel Jacobowitz <dan@codesourcery.com>
* elfread.c (elf_symtab_read): Treat weak functions as global.
2006-12-01 Daniel Jacobowitz <dan@codesourcery.com>
* gdb.base/solib-weak.c, gdb.base/solib-weak.exp, gdb.base/weaklib1.c,
gdb.base/weaklib2.c: New files.
Index: elfread.c
===================================================================
RCS file: /cvs/src/src/gdb/elfread.c,v
retrieving revision 1.55
diff -u -p -r1.55 elfread.c
--- elfread.c 21 Feb 2006 20:38:48 -0000 1.55
+++ elfread.c 1 Dec 2006 18:10:05 -0000
@@ -284,7 +284,7 @@ elf_symtab_read (struct objfile *objfile
}
else if (sym->section->flags & SEC_CODE)
{
- if (sym->flags & BSF_GLOBAL)
+ if (sym->flags & (BSF_GLOBAL | BSF_WEAK))
{
ms_type = mst_text;
}
Index: testsuite/gdb.base/solib-weak.c
===================================================================
RCS file: testsuite/gdb.base/solib-weak.c
diff -N testsuite/gdb.base/solib-weak.c
--- /dev/null 1 Jan 1970 00:00:00 -0000
+++ testsuite/gdb.base/solib-weak.c 1 Dec 2006 18:10:05 -0000
@@ -0,0 +1,25 @@
+/* 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. */
+
+int
+main()
+{
+ foo ();
+ return 0;
+}
Index: testsuite/gdb.base/solib-weak.exp
===================================================================
RCS file: testsuite/gdb.base/solib-weak.exp
diff -N testsuite/gdb.base/solib-weak.exp
--- /dev/null 1 Jan 1970 00:00:00 -0000
+++ testsuite/gdb.base/solib-weak.exp 1 Dec 2006 18:10:05 -0000
@@ -0,0 +1,109 @@
+# 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.
+
+# Test setting breakpoints on shared library functions provided by more
+# than one shared library, when one of the implementations is a "weak"
+# symbol. GDB should set a breakpoint at the first copy it finds.
+
+# Don't try to run shared library test cases on a remote target for now.
+if ![isnative] then {
+ return 0
+}
+
+# This test uses GCC-specific syntax.
+if [get_compiler_info not-used] {
+ return -1
+}
+
+if {![test_compiler_info "gcc-*"]} {
+ return 0
+}
+
+proc do_test { lib1opts lib2opts lib1first } {
+ global objdir srcdir subdir
+
+ set testopts ""
+ if {$lib1opts == ""} {
+ append testopts "lib1 nodebug, "
+ } else {
+ append testopts "lib1 debug, "
+ }
+ if {$lib2opts == ""} {
+ append testopts "lib2 nodebug, "
+ } else {
+ append testopts "lib2 debug, "
+ }
+ if {$lib1first} {
+ append testopts "lib1 first"
+ } else {
+ append testopts "lib2 first"
+ }
+
+ set testfile "solib-weak"
+ set srcfile ${testfile}.c
+ set binfile ${objdir}/${subdir}/${testfile}
+
+ set libfile1 "weaklib1"
+ set libfile2 "weaklib2"
+ set lib1src ${srcdir}/${subdir}/${libfile1}.c
+ set lib2src ${srcdir}/${subdir}/${libfile2}.c
+ set lib1 ${objdir}/${subdir}/${libfile1}.sl
+ set lib2 ${objdir}/${subdir}/${libfile2}.sl
+
+ if $lib1first {
+ set exec_opts [list debug shlib=${lib1} shlib=${lib2}]
+ set expected_file ${libfile1}
+ } else {
+ set exec_opts [list debug shlib=${lib2} shlib=${lib1}]
+ set expected_file ${libfile2}
+ }
+
+ if { [gdb_compile_shlib ${lib1src} ${lib1} ${lib1opts}] != ""
+ || [gdb_compile_shlib ${lib2src} ${lib2} ${lib2opts}] != ""
+ || [gdb_compile "${srcdir}/${subdir}/${srcfile}" ${binfile} executable $exec_opts] != ""} {
+ return -1
+ }
+
+ gdb_exit
+ gdb_start
+ gdb_reinitialize_dir $srcdir/$subdir
+ gdb_load ${binfile}
+
+ runto_main
+
+ gdb_breakpoint "bar"
+
+ # If the library which will be used is compiled without debugging
+ # information, GDB will pick the wrong copy of "bar", i.e. the one
+ # with debugging information.
+
+ if {(${lib1opts} == "" && ${lib2opts} != "" && ${lib1first} == 1)
+ || (${lib1opts} != "" && ${lib2opts} == "" && ${lib1first} == 0)} {
+ setup_kfail *-*-* gdb/1824
+ }
+
+ gdb_test "continue" "Breakpoint .* bar .*${expected_file}\\..*" \
+ "run to breakpoint - $testopts"
+}
+
+foreach lib1opts {{} {debug}} {
+ foreach lib2opts {{} {debug}} {
+ foreach lib1first {1 0} {
+ do_test $lib1opts $lib2opts $lib1first
+ }
+ }
+}
Index: testsuite/gdb.base/weaklib1.c
===================================================================
RCS file: testsuite/gdb.base/weaklib1.c
diff -N testsuite/gdb.base/weaklib1.c
--- /dev/null 1 Jan 1970 00:00:00 -0000
+++ testsuite/gdb.base/weaklib1.c 1 Dec 2006 18:10:05 -0000
@@ -0,0 +1,24 @@
+/* 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. */
+
+void __attribute__((weak))
+bar (void)
+{
+ puts ("bar in u1");
+}
Index: testsuite/gdb.base/weaklib2.c
===================================================================
RCS file: testsuite/gdb.base/weaklib2.c
diff -N testsuite/gdb.base/weaklib2.c
--- /dev/null 1 Jan 1970 00:00:00 -0000
+++ testsuite/gdb.base/weaklib2.c 1 Dec 2006 18:10:05 -0000
@@ -0,0 +1,31 @@
+/* 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. */
+
+void bar (void);
+void
+foo (void)
+{
+ bar ();
+}
+
+void
+bar (void)
+{
+ puts ("bar in u2");
+}