Re: [RFA/symtab] Handle weak functions as global

[Daniel Jacobowitz <drow at false dot 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");
+}