[patch] Fix C `extern' shadowing in a local block

[patch] Fix C `extern' shadowing in a local block

[Jan Kratochvil]

Hi,

fix GDB evaluation for:
{
  int var = 1;
  {
    extern int var;

    Access "var" at this point from GDB which must access the `extern' variable.
  }
}

Such code will still not work due to GCC PR debug/39563.  GCC may also fix it
a way compatible with current GDB (`extern var' to be global and use
DW_TAG_imported_declaration in the local block).  Still IMO a valid DWARF
layout used in the attached .S testcase currently fails for GDB.

The testcase was written primarily as currently removing LOC_UNRESOLVED from
the GDB codebase had no effect on the testsuite results.

I did remove LOC_UNRESOLVED before but that patch was wrong (+got no replies):
  http://sourceware.org/ml/gdb-patches/2008-08/msg00117.html

Maybe during LOC_UNRESOLVED parsing GDB could already lookup the minimal
symbol and create LOC_STATIC instead (but what to create for TLS minimal
symbols?).  Did not try this way but it would remove LOC_UNRESOLVED.

No regressions on x86_64-unknown-linux-gnu.


Thanks,
Jan


gdb/
2009-03-26  Jan Kratochvil  <jan.kratochvil@redhat.com>

	* dwarf2read.c
	(new_symbol <DW_TAG_variable> <!DW_AT_location> <DW_AT_external>):
	Create the symbol in local scope.
	* symtab.h (cu->list_in_scope <LOC_UNRESOLVED>): New comment part.

gdb/testsuite/
2009-03-26  Jan Kratochvil  <jan.kratochvil@redhat.com>

	* gdb.dwarf2/dw2-unresolved-main.c, gdb.dwarf2/dw2-unresolved.S,
	gdb.dwarf2/dw2-unresolved.exp: New.

--- gdb/dwarf2read.c	26 Mar 2009 14:47:18 -0000	1.298
+++ gdb/dwarf2read.c	26 Mar 2009 21:09:04 -0000
@@ -7657,7 +7657,7 @@ new_symbol (struct die_info *die, struct
 		  && dwarf2_attr (die, DW_AT_type, cu) != NULL)
 		{
 		  SYMBOL_CLASS (sym) = LOC_UNRESOLVED;
-		  add_symbol_to_list (sym, &global_symbols);
+		  add_symbol_to_list (sym, cu->list_in_scope);
 		}
 	      else if (!die_is_declaration (die, cu))
 		{
--- gdb/symtab.h	6 Feb 2009 21:33:58 -0000	1.135
+++ gdb/symtab.h	26 Mar 2009 21:09:04 -0000
@@ -472,7 +472,13 @@ enum address_class
      in another object file or runtime common storage.
      The linker might even remove the minimal symbol if the global
      symbol is never referenced, in which case the symbol remains
-     unresolved.  */
+     unresolved.
+     
+     GDB would normally find the symbol in the minimal symbol table if it will
+     not find it in the full symbol table.  But a reference to an external
+     symbol in a local block shadowing other definition requires full symbol
+     without possibly having its address available for LOC_STATIC.  Testcase
+     is provided as `gdb.dwarf2/dw2-unresolved.exp'.  */
 
   LOC_UNRESOLVED,
 
--- /dev/null	1 Jan 1970 00:00:00 -0000
+++ gdb/testsuite/gdb.dwarf2/dw2-unresolved-main.c	26 Mar 2009 21:09:05 -0000
@@ -0,0 +1,46 @@
+/* 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/>.  */
+
+#include <stdlib.h>
+
+asm (".globl cu_text_start");
+asm ("cu_text_start:");
+
+int
+main (void)
+{
+  unsigned char var = 1;
+
+  if (var != 1)
+    abort ();
+  {
+    extern unsigned char var;
+
+    /* Do not rely on the `extern' DIE output by GCC (GCC PR debug/39563).  */
+asm (".globl extern_block_start");
+asm ("extern_block_start:");
+    if (var != 2)
+      abort ();
+asm (".globl extern_block_end");
+asm ("extern_block_end:");
+  }
+
+  return 0;
+}
+
+asm (".globl cu_text_end");
+asm ("cu_text_end:");
--- /dev/null	1 Jan 1970 00:00:00 -0000
+++ gdb/testsuite/gdb.dwarf2/dw2-unresolved.S	26 Mar 2009 21:09:05 -0000
@@ -0,0 +1,171 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2007, 2008, 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/>.  */
+
+	.data
+
+/* VAR1 is wrong here, in the real inferior it is located on stack.  As both
+   places are never modified and they are initialized to the same value it
+   makes no difference.  Ensure the name clash for "var".  */
+var1:	.byte	1
+
+	.globl	var
+var:	.byte	2
+
+/* Debug information */
+
+	.section .debug_info
+.Lcu1_begin:
+	/* CU header */
+	.4byte	.Lcu1_end - .Lcu1_start		/* Length of Compilation Unit */
+.Lcu1_start:
+	.2byte	2				/* DWARF Version */
+	.4byte	.Labbrev1_begin			/* Offset into abbrev section */
+	.byte	4				/* Pointer size */
+
+	/* CU die */
+	.uleb128 1				/* Abbrev: DW_TAG_compile_unit */
+	.4byte	cu_text_end			/* DW_AT_high_pc */
+	.4byte	cu_text_start			/* DW_AT_low_pc */
+	.ascii	"dw2-unresolved-main.c\0"	/* DW_AT_name */
+	.ascii	"GNU C 4.3.2\0"			/* DW_AT_producer */
+	.byte	1				/* DW_AT_language (C) */
+
+.Ltype_uchar:
+	.uleb128	2			/* Abbrev: DW_TAG_base_type */
+	.ascii		"unsigned char\0"	/* DW_AT_name */
+	.byte		1			/* DW_AT_byte_size */
+	.byte		7			/* DW_AT_encoding */
+
+	/* main */
+	.uleb128	3			/* Abbrev: DW_TAG_subprogram */
+	.byte		1			/* DW_AT_decl_file */
+	.byte		2			/* DW_AT_decl_line */
+	.ascii		"main\0"		/* DW_AT_name */
+	.4byte		.Ltype_uchar-.Lcu1_begin	/* DW_AT_type */
+	.4byte		cu_text_start		/* DW_AT_low_pc */
+	.4byte		cu_text_end		/* DW_AT_high_pc */
+
+	.uleb128	4			/* Abbrev: DW_TAG_variable (location) */
+	.ascii		"var\0"			/* DW_AT_name */
+	.byte		2f - 1f			/* DW_AT_location */
+1:	.byte		3			/*   DW_OP_addr */
+/* See VAR1 definition why this DIE is not correct.  */
+	.4byte		var1			/*   <addr> */
+2:	.4byte		.Ltype_uchar-.Lcu1_begin	/* DW_AT_type */
+
+	.uleb128	6			/* Abbrev: DW_TAG_lexical_block */
+	.4byte		extern_block_start	/* DW_AT_low_pc */
+	.4byte		extern_block_end	/* DW_AT_high_pc */
+
+	.uleb128	5			/* Abbrev: DW_TAG_variable (extern) */
+	.ascii		"var\0"			/* DW_AT_name */
+	.4byte		.Ltype_uchar-.Lcu1_begin	/* DW_AT_type */
+	.byte		1			/* DW_AT_external */
+
+	.byte		0			/* End of children of the lexical block */
+
+	.byte		0			/* End of children of main */
+
+	.byte		0			/* End of children of CU */
+
+.Lcu1_end:
+
+/* Abbrev table */
+	.section .debug_abbrev
+.Labbrev1_begin:
+	.uleb128	1			/* Abbrev code */
+	.uleb128	0x11			/* DW_TAG_compile_unit */
+	.byte		1			/* has_children */
+	.uleb128	0x12			/* DW_AT_high_pc */
+	.uleb128	0x1			/* DW_FORM_addr */
+	.uleb128	0x11			/* DW_AT_low_pc */
+	.uleb128	0x1			/* DW_FORM_addr */
+	.uleb128	0x3			/* DW_AT_name */
+	.uleb128	0x8			/* DW_FORM_string */
+	.uleb128	0x25			/* DW_AT_producer */
+	.uleb128	0x8			/* DW_FORM_string */
+	.uleb128	0x13			/* DW_AT_language */
+	.uleb128	0xb			/* DW_FORM_data1 */
+	.byte		0x0			/* Terminator */
+	.byte		0x0			/* Terminator */
+
+	.uleb128	2			/* Abbrev code */
+	.uleb128	0x24			/* DW_TAG_base_type */
+	.byte		0			/* has_children */
+	.uleb128	0x3			/* DW_AT_name */
+	.uleb128	0x8			/* DW_FORM_string */
+	.uleb128	0xb			/* DW_AT_byte_size */
+	.uleb128	0xb			/* DW_FORM_data1 */
+	.uleb128	0x3e			/* DW_AT_encoding */
+	.uleb128	0xb			/* DW_FORM_data1 */
+	.byte		0x0			/* Terminator */
+	.byte		0x0			/* Terminator */
+
+	.uleb128	3			/* Abbrev code */
+	.uleb128	0x2e			/* DW_TAG_subprogram */
+	.byte		1			/* has_children */
+	.uleb128	0x3a			/* DW_AT_decl_file */
+	.uleb128	0xb			/* DW_FORM_data1 */
+	.uleb128	0x3b			/* DW_AT_decl_line */
+	.uleb128	0xb			/* DW_FORM_data1 */
+	.uleb128	0x3			/* DW_AT_name */
+	.uleb128	0x8			/* DW_FORM_string */
+	.uleb128	0x49			/* DW_AT_type */
+	.uleb128	0x13			/* DW_FORM_ref4 */
+	.uleb128	0x11			/* DW_AT_low_pc */
+	.uleb128	0x1			/* DW_FORM_addr */
+	.uleb128	0x12			/* DW_AT_high_pc */
+	.uleb128	0x1			/* DW_FORM_addr */
+	.byte		0x0			/* Terminator */
+	.byte		0x0			/* Terminator */
+
+	.uleb128	4			/* Abbrev code (location) */
+	.uleb128	0x34			/* DW_TAG_variable */
+	.byte		0			/* has_children */
+	.uleb128	0x3			/* DW_AT_name */
+	.uleb128	0x8			/* DW_FORM_string */
+	.uleb128	0x2			/* DW_AT_location */
+	.uleb128	0xa			/* DW_FORM_block1 */
+	.uleb128	0x49			/* DW_AT_type */
+	.uleb128	0x13			/* DW_FORM_ref4 */
+	.byte		0x0			/* Terminator */
+	.byte		0x0			/* Terminator */
+
+	.uleb128	5			/* Abbrev code (extern) */
+	.uleb128	0x34			/* DW_TAG_variable */
+	.byte		0			/* has_children */
+	.uleb128	0x3			/* DW_AT_name */
+	.uleb128	0x8			/* DW_FORM_string */
+	.uleb128	0x49			/* DW_AT_type */
+	.uleb128	0x13			/* DW_FORM_ref4 */
+	.uleb128	0x3f			/* DW_AT_external */
+	.uleb128	0xc			/* DW_FORM_flag */
+	.byte		0x0			/* Terminator */
+	.byte		0x0			/* Terminator */
+
+	.uleb128	6			/* Abbrev code */
+	.uleb128	0x0b			/* DW_TAG_lexical_block */
+	.byte		1			/* has_children */
+	.uleb128	0x11			/* DW_AT_low_pc */
+	.uleb128	0x1			/* DW_FORM_addr */
+	.uleb128	0x12			/* DW_AT_high_pc */
+	.uleb128	0x1			/* DW_FORM_addr */
+	.byte		0x0			/* Terminator */
+	.byte		0x0			/* Terminator */
+
+	.byte		0x0			/* Terminator */
+	.byte		0x0			/* Terminator */
--- /dev/null	1 Jan 1970 00:00:00 -0000
+++ gdb/testsuite/gdb.dwarf2/dw2-unresolved.exp	26 Mar 2009 21:09:05 -0000
@@ -0,0 +1,41 @@
+# 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/>.
+
+# This test can only be run on targets which support DWARF-2 and use gas.
+# For now pick a sampling of likely targets.
+if {![istarget *-*-linux*]
+    && ![istarget *-*-gnu*]
+    && ![istarget *-*-elf*]
+    && ![istarget *-*-openbsd*]
+    && ![istarget arm-*-eabi*]
+    && ![istarget powerpc-*-eabi*]} {
+    return 0  
+}
+
+if { [prepare_for_testing dw2-unresolved.exp "dw2-unresolved" {dw2-unresolved-main.c dw2-unresolved.S} {nodebug}] } {
+    return -1
+}
+
+if ![runto_main] {
+    return -1
+}
+
+# This testcase tests LOC_UNRESOLVED works right.
+
+gdb_breakpoint "*extern_block_start"
+gdb_continue_to_breakpoint "*extern_block_start"
+
+# Expect the inner value 2.  Value 1 from the outer local block is shadowed.
+gdb_test "print var" "= 2( '.*')?"

Re: [patch] Fix C `extern' shadowing in a local block

[Jan Kratochvil]

On Thu, 26 Mar 2009 22:21:28 +0100, Jan Kratochvil wrote:
> fix GDB evaluation for:
> {
>   int var = 1;
>   {
>     extern int var;
> 
>     Access "var" at this point from GDB which must access the `extern' variable.
>   }
> }
> 
> Such code will still not work due to GCC PR debug/39563.  GCC may also fix it
> a way compatible with current GDB (`extern var' to be global and use
> DW_TAG_imported_declaration in the local block).  Still IMO a valid DWARF
> layout used in the attached .S testcase currently fails for GDB.

The patch provided for GCC (but still not checked-in) requires fixed GDB:
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39563#c5


Thanks,
Jan

Re: [patch] Fix C `extern' shadowing in a local block

[Joel Brobecker]

Hi Jan,

> 2009-03-26  Jan Kratochvil  <jan.kratochvil@redhat.com>
> 
> 	* dwarf2read.c
> 	(new_symbol <DW_TAG_variable> <!DW_AT_location> <DW_AT_external>):
> 	Create the symbol in local scope.

This part makes me uncomfortable. I am afraid that doing so would be
misinterpreting the meaning of DW_AT_external. Also, I would mean
that we are treating this attribute differently depending on whether
we have a location attribute or not. This may be the correct thing
to do, but I want to make sure that the debugging information generated
in this case is correct.

We have to consider for instance the following example:

    extern int toto;
    
    int
    main (void)
    {
      toto++;
      return 0;
    }

The debugging information generated for our extern looks like this:

        .uleb128 0x4    # (DIE (0x55) DW_TAG_variable)
        .long   .LASF4  # DW_AT_name: "toto"
        .byte   0x1     # DW_AT_decl_file (foo.c)
        .byte   0x1     # DW_AT_decl_line
        .long   0x4e    # DW_AT_type
        .byte   0x1     # DW_AT_external
        .byte   0x1     # DW_AT_declaration
        .byte   0x0     # end of children of DIE 0xb

The description for the global variable looks completely identical
to your example where the variable is bound to a local scope.

Now, in practice, I think that things would work in both cases.
In my example, with your patch, the variable would be inserted
at the file_symbols level instead of inside the local scope associated
to your block.

I would like to have Daniel's opinion on this. I'll see if he's on IRC.

-- 
Joel

Re: [patch] Fix C `extern' shadowing in a local block

[Daniel Jacobowitz]

On Thu, Apr 02, 2009 at 11:54:13AM -0700, Joel Brobecker wrote:
> This part makes me uncomfortable. I am afraid that doing so would be
> misinterpreting the meaning of DW_AT_external.

I think that this is what DW_AT_external means: the declaration
represents an externally visible variable.

> Also, I would mean
> that we are treating this attribute differently depending on whether
> we have a location attribute or not.

This bothers me too, but I think it's OK.  A local scope definition of
an external variable with a location is an odd concept, and until I
see an example that produces one, I have no idea what we should do
with it.  The only one I can think of would be a declaration (not
definition) with location:

  DW_TAG_variable
    DW_AT_name: bar
    DW_AT_external: 1
    DW_AT_declaration: 1
    DW_AT_location: &bar

But I don't think anyone produces that.

I took a look at our LOC_UNRESOLVED handling; I don't think it's quite
wise, since it ignores the full symbol table, but in practice that's
fine for unstripped binaries.

-- 
Daniel Jacobowitz
CodeSourcery

Re: [patch] Fix C `extern' shadowing in a local block

[Jan Kratochvil]

Hi Joel and Daniel,

thanks for the verification, checked-in.

print/d fix has been suggested by Pedro Alves.


Regards,
Jan


http://sourceware.org/ml/gdb-cvs/2009-04/msg00021.html

gdb/
2009-04-02  Jan Kratochvil  <jan.kratochvil@redhat.com>

	* dwarf2read.c
	(new_symbol <DW_TAG_variable> <!DW_AT_location> <DW_AT_external>):
	Create the symbol in local scope.
	* symtab.h (cu->list_in_scope <LOC_UNRESOLVED>): New comment part.

gdb/testsuite/
2009-04-02  Jan Kratochvil  <jan.kratochvil@redhat.com>

	* gdb.dwarf2/dw2-unresolved-main.c, gdb.dwarf2/dw2-unresolved.S,
	gdb.dwarf2/dw2-unresolved.exp: New.

--- src/gdb/dwarf2read.c	2009/03/31 20:21:07	1.299
+++ src/gdb/dwarf2read.c	2009/04/02 21:01:40	1.300
@@ -7682,7 +7682,7 @@
 		  && dwarf2_attr (die, DW_AT_type, cu) != NULL)
 		{
 		  SYMBOL_CLASS (sym) = LOC_UNRESOLVED;
-		  add_symbol_to_list (sym, &global_symbols);
+		  add_symbol_to_list (sym, cu->list_in_scope);
 		}
 	      else if (!die_is_declaration (die, cu))
 		{
--- src/gdb/symtab.h	2009/02/06 21:33:58	1.135
+++ src/gdb/symtab.h	2009/04/02 21:01:40	1.136
@@ -472,7 +472,13 @@
      in another object file or runtime common storage.
      The linker might even remove the minimal symbol if the global
      symbol is never referenced, in which case the symbol remains
-     unresolved.  */
+     unresolved.
+     
+     GDB would normally find the symbol in the minimal symbol table if it will
+     not find it in the full symbol table.  But a reference to an external
+     symbol in a local block shadowing other definition requires full symbol
+     without possibly having its address available for LOC_STATIC.  Testcase
+     is provided as `gdb.dwarf2/dw2-unresolved.exp'.  */
 
   LOC_UNRESOLVED,
 
--- src/gdb/testsuite/gdb.dwarf2/dw2-unresolved-main.c
+++ src/gdb/testsuite/gdb.dwarf2/dw2-unresolved-main.c	2009-04-02 21:02:18.535807000 +0000
@@ -0,0 +1,46 @@
+/* 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/>.  */
+
+#include <stdlib.h>
+
+asm (".globl cu_text_start");
+asm ("cu_text_start:");
+
+int
+main (void)
+{
+  unsigned char var = 1;
+
+  if (var != 1)
+    abort ();
+  {
+    extern unsigned char var;
+
+    /* Do not rely on the `extern' DIE output by GCC (GCC PR debug/39563).  */
+asm (".globl extern_block_start");
+asm ("extern_block_start:");
+    if (var != 2)
+      abort ();
+asm (".globl extern_block_end");
+asm ("extern_block_end:");
+  }
+
+  return 0;
+}
+
+asm (".globl cu_text_end");
+asm ("cu_text_end:");
--- src/gdb/testsuite/gdb.dwarf2/dw2-unresolved.S
+++ src/gdb/testsuite/gdb.dwarf2/dw2-unresolved.S	2009-04-02 21:02:19.630621000 +0000
@@ -0,0 +1,171 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2007, 2008, 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/>.  */
+
+	.data
+
+/* VAR1 is wrong here, in the real inferior it is located on stack.  As both
+   places are never modified and they are initialized to the same value it
+   makes no difference.  Ensure the name clash for "var".  */
+var1:	.byte	1
+
+	.globl	var
+var:	.byte	2
+
+/* Debug information */
+
+	.section .debug_info
+.Lcu1_begin:
+	/* CU header */
+	.4byte	.Lcu1_end - .Lcu1_start		/* Length of Compilation Unit */
+.Lcu1_start:
+	.2byte	2				/* DWARF Version */
+	.4byte	.Labbrev1_begin			/* Offset into abbrev section */
+	.byte	4				/* Pointer size */
+
+	/* CU die */
+	.uleb128 1				/* Abbrev: DW_TAG_compile_unit */
+	.4byte	cu_text_end			/* DW_AT_high_pc */
+	.4byte	cu_text_start			/* DW_AT_low_pc */
+	.ascii	"dw2-unresolved-main.c\0"	/* DW_AT_name */
+	.ascii	"GNU C 4.3.2\0"			/* DW_AT_producer */
+	.byte	1				/* DW_AT_language (C) */
+
+.Ltype_uchar:
+	.uleb128	2			/* Abbrev: DW_TAG_base_type */
+	.ascii		"unsigned char\0"	/* DW_AT_name */
+	.byte		1			/* DW_AT_byte_size */
+	.byte		7			/* DW_AT_encoding */
+
+	/* main */
+	.uleb128	3			/* Abbrev: DW_TAG_subprogram */
+	.byte		1			/* DW_AT_decl_file */
+	.byte		2			/* DW_AT_decl_line */
+	.ascii		"main\0"		/* DW_AT_name */
+	.4byte		.Ltype_uchar-.Lcu1_begin	/* DW_AT_type */
+	.4byte		cu_text_start		/* DW_AT_low_pc */
+	.4byte		cu_text_end		/* DW_AT_high_pc */
+
+	.uleb128	4			/* Abbrev: DW_TAG_variable (location) */
+	.ascii		"var\0"			/* DW_AT_name */
+	.byte		2f - 1f			/* DW_AT_location */
+1:	.byte		3			/*   DW_OP_addr */
+/* See VAR1 definition why this DIE is not correct.  */
+	.4byte		var1			/*   <addr> */
+2:	.4byte		.Ltype_uchar-.Lcu1_begin	/* DW_AT_type */
+
+	.uleb128	6			/* Abbrev: DW_TAG_lexical_block */
+	.4byte		extern_block_start	/* DW_AT_low_pc */
+	.4byte		extern_block_end	/* DW_AT_high_pc */
+
+	.uleb128	5			/* Abbrev: DW_TAG_variable (extern) */
+	.ascii		"var\0"			/* DW_AT_name */
+	.4byte		.Ltype_uchar-.Lcu1_begin	/* DW_AT_type */
+	.byte		1			/* DW_AT_external */
+
+	.byte		0			/* End of children of the lexical block */
+
+	.byte		0			/* End of children of main */
+
+	.byte		0			/* End of children of CU */
+
+.Lcu1_end:
+
+/* Abbrev table */
+	.section .debug_abbrev
+.Labbrev1_begin:
+	.uleb128	1			/* Abbrev code */
+	.uleb128	0x11			/* DW_TAG_compile_unit */
+	.byte		1			/* has_children */
+	.uleb128	0x12			/* DW_AT_high_pc */
+	.uleb128	0x1			/* DW_FORM_addr */
+	.uleb128	0x11			/* DW_AT_low_pc */
+	.uleb128	0x1			/* DW_FORM_addr */
+	.uleb128	0x3			/* DW_AT_name */
+	.uleb128	0x8			/* DW_FORM_string */
+	.uleb128	0x25			/* DW_AT_producer */
+	.uleb128	0x8			/* DW_FORM_string */
+	.uleb128	0x13			/* DW_AT_language */
+	.uleb128	0xb			/* DW_FORM_data1 */
+	.byte		0x0			/* Terminator */
+	.byte		0x0			/* Terminator */
+
+	.uleb128	2			/* Abbrev code */
+	.uleb128	0x24			/* DW_TAG_base_type */
+	.byte		0			/* has_children */
+	.uleb128	0x3			/* DW_AT_name */
+	.uleb128	0x8			/* DW_FORM_string */
+	.uleb128	0xb			/* DW_AT_byte_size */
+	.uleb128	0xb			/* DW_FORM_data1 */
+	.uleb128	0x3e			/* DW_AT_encoding */
+	.uleb128	0xb			/* DW_FORM_data1 */
+	.byte		0x0			/* Terminator */
+	.byte		0x0			/* Terminator */
+
+	.uleb128	3			/* Abbrev code */
+	.uleb128	0x2e			/* DW_TAG_subprogram */
+	.byte		1			/* has_children */
+	.uleb128	0x3a			/* DW_AT_decl_file */
+	.uleb128	0xb			/* DW_FORM_data1 */
+	.uleb128	0x3b			/* DW_AT_decl_line */
+	.uleb128	0xb			/* DW_FORM_data1 */
+	.uleb128	0x3			/* DW_AT_name */
+	.uleb128	0x8			/* DW_FORM_string */
+	.uleb128	0x49			/* DW_AT_type */
+	.uleb128	0x13			/* DW_FORM_ref4 */
+	.uleb128	0x11			/* DW_AT_low_pc */
+	.uleb128	0x1			/* DW_FORM_addr */
+	.uleb128	0x12			/* DW_AT_high_pc */
+	.uleb128	0x1			/* DW_FORM_addr */
+	.byte		0x0			/* Terminator */
+	.byte		0x0			/* Terminator */
+
+	.uleb128	4			/* Abbrev code (location) */
+	.uleb128	0x34			/* DW_TAG_variable */
+	.byte		0			/* has_children */
+	.uleb128	0x3			/* DW_AT_name */
+	.uleb128	0x8			/* DW_FORM_string */
+	.uleb128	0x2			/* DW_AT_location */
+	.uleb128	0xa			/* DW_FORM_block1 */
+	.uleb128	0x49			/* DW_AT_type */
+	.uleb128	0x13			/* DW_FORM_ref4 */
+	.byte		0x0			/* Terminator */
+	.byte		0x0			/* Terminator */
+
+	.uleb128	5			/* Abbrev code (extern) */
+	.uleb128	0x34			/* DW_TAG_variable */
+	.byte		0			/* has_children */
+	.uleb128	0x3			/* DW_AT_name */
+	.uleb128	0x8			/* DW_FORM_string */
+	.uleb128	0x49			/* DW_AT_type */
+	.uleb128	0x13			/* DW_FORM_ref4 */
+	.uleb128	0x3f			/* DW_AT_external */
+	.uleb128	0xc			/* DW_FORM_flag */
+	.byte		0x0			/* Terminator */
+	.byte		0x0			/* Terminator */
+
+	.uleb128	6			/* Abbrev code */
+	.uleb128	0x0b			/* DW_TAG_lexical_block */
+	.byte		1			/* has_children */
+	.uleb128	0x11			/* DW_AT_low_pc */
+	.uleb128	0x1			/* DW_FORM_addr */
+	.uleb128	0x12			/* DW_AT_high_pc */
+	.uleb128	0x1			/* DW_FORM_addr */
+	.byte		0x0			/* Terminator */
+	.byte		0x0			/* Terminator */
+
+	.byte		0x0			/* Terminator */
+	.byte		0x0			/* Terminator */
--- src/gdb/testsuite/gdb.dwarf2/dw2-unresolved.exp
+++ src/gdb/testsuite/gdb.dwarf2/dw2-unresolved.exp	2009-04-02 21:02:20.918871000 +0000
@@ -0,0 +1,41 @@
+# 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/>.
+
+# This test can only be run on targets which support DWARF-2 and use gas.
+# For now pick a sampling of likely targets.
+if {![istarget *-*-linux*]
+    && ![istarget *-*-gnu*]
+    && ![istarget *-*-elf*]
+    && ![istarget *-*-openbsd*]
+    && ![istarget arm-*-eabi*]
+    && ![istarget powerpc-*-eabi*]} {
+    return 0  
+}
+
+if { [prepare_for_testing dw2-unresolved.exp "dw2-unresolved" {dw2-unresolved-main.c dw2-unresolved.S} {nodebug}] } {
+    return -1
+}
+
+if ![runto_main] {
+    return -1
+}
+
+# This testcase tests LOC_UNRESOLVED works right.
+
+gdb_breakpoint "*extern_block_start"
+gdb_continue_to_breakpoint "*extern_block_start"
+
+# Expect the inner value 2.  Value 1 from the outer local block is shadowed.
+gdb_test "print/d var" "= 2"