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

[Jan Kratochvil <jan dot kratochvil at redhat dot com>]

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( '.*')?"