[RFA/symtab] Handle weak functions as global

[RFA/symtab] Handle weak functions as global

[Daniel Jacobowitz]

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.

Is this patch OK?

-- 
Daniel Jacobowitz

2004-11-01  Daniel Jacobowitz  <dan@debian.org>

	* elfread.c (elf_symtab_read): Treat weak functions as global.

Index: elfread.c
===================================================================
RCS file: /big/fsf/rsync/src-cvs/src/gdb/elfread.c,v
retrieving revision 1.47
diff -u -p -r1.47 elfread.c
--- elfread.c	23 Oct 2004 16:18:08 -0000	1.47
+++ elfread.c	1 Nov 2004 17:00:39 -0000
@@ -305,7 +305,7 @@ 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;
 		    }

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

[Elena Zannoni]

Daniel Jacobowitz writes:
 > 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.
 > 

Interesting. This is just gdb not following in the symbol searches any
of the ELF scoping rules. Can you add a small testcase?

How about:

file1.c
---
void
bar (void)
{
  puts ("bar in u1");
}


file2.c
---
void bar (void);
void
foo (void)
{
  bar ();
}
 
void
bar (void)
{
  puts ("bar in u2");
}


foo.c
---
int
main()
{
  foo ();
  return 0;
}


If you compile the files with bar() as shared libraries, what version
of bar does gdb pick from main?



 > Is this patch OK?
 > 

Does it effect the testcase above?


 > -- 
 > Daniel Jacobowitz
 > 
 > 2004-11-01  Daniel Jacobowitz  <dan@debian.org>
 > 
 > 	* elfread.c (elf_symtab_read): Treat weak functions as global.
 > 
 > Index: elfread.c
 > ===================================================================
 > RCS file: /big/fsf/rsync/src-cvs/src/gdb/elfread.c,v
 > retrieving revision 1.47
 > diff -u -p -r1.47 elfread.c
 > --- elfread.c	23 Oct 2004 16:18:08 -0000	1.47
 > +++ elfread.c	1 Nov 2004 17:00:39 -0000
 > @@ -305,7 +305,7 @@ 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;
 >  		    }

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

[Daniel Jacobowitz]

On Sun, Nov 28, 2004 at 09:08:32PM -0500, Elena Zannoni wrote:
> Interesting. This is just gdb not following in the symbol searches any
> of the ELF scoping rules. Can you add a small testcase?

I'll have to limit it to GCC - the patch only affects weak symbols. 
Here's a test case; one unexpected failure without the patch, none
with.  Two known failures (see below).

> If you compile the files with bar() as shared libraries, what version
> of bar does gdb pick from main?

The right one, with or without the patch - if you link the library
contaning file1 first on the command line, it breaks in file1.c,
otherwise it breaks in file2.c.  I think you could get GDB to give the
wrong answer with more complicated tests - for instance using dlopen.
Like you said, GDB doesn't know anything about ELF scoping (and I don't
think it could know everything about it, either - does the link map
expose enough information about search order?).

The only way I could get the test to work was by using a weak symbol
and building the shared libraries without debug information.  This
patch only changes the minsym type; with debug information,
lookup_minimal_symbol is never called.  The original problem came up
because "open" is an assembly stub in GDB.

This exposed a related problem, which I've filed as gdb/1824.  If one
has debug and the other doesn't, lookup_symbol will succeed, and we'll
always breakpoint the full symbol.  Global minimal symbols could
be handled before static full symbols, one object at a time.  Or, as I
suggest in the bug report, we could just breakpoint both copies.  I
suspect that's more robust and more useful.

Testcase look OK?  I finally added some shared library utility code to
gdb.exp.

-- 
Daniel Jacobowitz

2004-11-30  Daniel Jacobowitz  <dan@debian.org>

	* gdb.base/solib-weak.c, gdb.base/solib-weak.exp, gdb.base/weaklib1.c,
	gdb.base/weaklib2.c: New files.
	* lib/gdb.exp (gdb_compile): Handle shlib=.
	(gdb_compile_shlib): New function.

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	30 Nov 2004 21:22:27 -0000
@@ -0,0 +1,25 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2004 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	30 Nov 2004 21:28:35 -0000
@@ -0,0 +1,109 @@
+#   Copyright 2004
+#   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 ${objdir}/${subdir}/solib-weak] {
+    return -1
+}
+
+if {$gcc_compiled == 0} {
+    return 0
+}
+
+proc do_test { lib1opts lib2opts lib1first } {
+    global objdir srcdir subdir
+
+    set testopts ""
+    if {$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	30 Nov 2004 21:22:26 -0000
@@ -0,0 +1,24 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2004 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	30 Nov 2004 21:22:26 -0000
@@ -0,0 +1,31 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2004 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");
+}                                                                                                       
Index: testsuite/lib/gdb.exp
===================================================================
RCS file: /big/fsf/rsync/src-cvs/src/gdb/testsuite/lib/gdb.exp,v
retrieving revision 1.58
diff -u -p -r1.58 gdb.exp
--- testsuite/lib/gdb.exp	10 Sep 2004 01:04:59 -0000	1.58
+++ testsuite/lib/gdb.exp	30 Nov 2004 21:24:17 -0000
@@ -1324,6 +1324,30 @@ proc gdb_compile {source dest type optio
     global gdb_wrapper_flags;
     global gdb_wrapper_initialized;
 
+    # Add platform-specific options if a shared library was specified using
+    # "shlib=librarypath" in OPTIONS.
+    set new_options ""
+    set shlib_found 0
+    foreach opt $options {
+	if [regexp {^shlib=(.*)} $opt dummy_var shlib_name] {
+	    lappend source $shlib_name
+	    if {$shlib_found == 0} {
+		set shlib_found 1
+		global gcc_compiled
+		if { ($gcc_compiled 
+		      &&  ([istarget "powerpc*-*-aix*"]
+			|| [istarget "rs6000*-*-aix*"] )) } {
+		    lappend options "additional_flags=-L${objdir}/${subdir}"
+		} elseif { [istarget "mips-sgi-irix*"] } {
+		    lappend options "additional_flags=-rpath ${objdir}/${subdir}"
+		}
+	    }
+	} else {
+	    lappend new_options $opt
+	}
+    }
+    set options $new_options
+
     if [target_info exists gdb_stub] {
 	set options2 { "additional_flags=-Dusestubs" }
 	lappend options "libs=[target_info gdb_stub]";
@@ -1434,6 +1458,50 @@ proc gdb_compile_objc {source dest type 
     }
 }
 
+# Build a shared library from SOURCES.  You must use get_compiler_info
+# first.
+
+proc gdb_compile_shlib {sources dest options} {
+    global gcc_compiled
+
+    set obj_options $options
+    if {$gcc_compiled == 0} {
+	if [istarget "hppa*-hp-hpux*"] then {
+	    lappend obj_options "additional_flags=+z"
+	} elseif { [istarget "mips-sgi-irix*"] } {
+	    # Disable SGI compiler's implicit -Dsgi
+	    lappend obj_options "additional_flags=-Usgi"
+	} else {
+	    # don't know what the compiler is...
+	}
+    } else {
+	if { !([istarget "powerpc*-*-aix*"]
+	       || [istarget "rs6000*-*-aix*"]) } {
+	    lappend obj_options "additional_flags=-fpic"
+	}
+    }
+
+    set outdir [file dirname $dest]
+    set objects ""
+    foreach source $sources {
+	set sourcebase [file tail $source]
+	if {[gdb_compile $source "${outdir}/${sourcebase}.o" object $obj_options] != ""} {
+	    return -1
+	}
+	lappend objects ${outdir}/${sourcebase}.o
+    }
+
+    if [istarget "hppa*-*-hpux*"] {
+	remote_exec build "ld -b ${objects} -o ${dest}"
+    } else {
+	set link_options options
+	lappend link_options "additional_flags=-shared"
+	if {[gdb_compile "${objects}" "${dest}" executable $link_options] != ""} {
+	    return -1
+	}
+    }
+}
+
 proc send_gdb { string } {
     global suppress_flag;
     if { $suppress_flag } {

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

[Daniel Jacobowitz]

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");
+}