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https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=185337
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2008-02-24  Jan Kratochvil  <jan.kratochvil@redhat.com>
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	Port to GDB-6.8pre.
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currently for trivial nonthreaded helloworld with no debug info up to -ggdb2 you
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will get:
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        (gdb) p errno
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        [some error]
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* with -ggdb2 and less "errno" in fact does not exist anywhere as it was
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  compiled to "(*__errno_location ())" and the macro definition is not present.
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  Unfortunately gdb will find the TLS symbol and it will try to access it but
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  as the program has been compiled without -lpthread the TLS base register
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  (%gs on i386) is not setup and it will result in:
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        Cannot access memory at address 0x8
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Attached suggestion patch how to deal with the most common "errno" symbol
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for the most common under-ggdb3 compiled programs.
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2007-11-03  Jan Kratochvil  <jan.kratochvil@redhat.com>
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	* ./gdb/dwarf2read.c (read_partial_die, dwarf2_linkage_name): Prefer
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	DW_AT_MIPS_linkage_name over DW_AT_name now only for non-C.
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glibc-debuginfo-2.7-2.x86_64: /usr/lib/debug/lib64/libc.so.6.debug:
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  <81a2>     DW_AT_name        : (indirect string, offset: 0x280e): __errno_location
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  <81a8>     DW_AT_MIPS_linkage_name: (indirect string, offset: 0x2808): *__GI___errno_location
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Index: gdb-6.8cvs20080219/gdb/dwarf2read.c
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===================================================================
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--- gdb-6.8cvs20080219.orig/gdb/dwarf2read.c	2008-02-19 17:27:21.000000000 +0100
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+++ gdb-6.8cvs20080219/gdb/dwarf2read.c	2008-02-20 13:35:19.000000000 +0100
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@@ -5679,8 +5679,8 @@ read_partial_die (struct partial_die_inf
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 	{
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 	case DW_AT_name:
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-	  /* Prefer DW_AT_MIPS_linkage_name over DW_AT_name.  */
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-	  if (part_die->name == NULL)
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+	  /* Prefer DW_AT_MIPS_linkage_name over DW_AT_name for non-C.  */
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+	  if (cu->language == language_c || part_die->name == NULL)
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 	    part_die->name = DW_STRING (&attr);
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 	  break;
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 	case DW_AT_comp_dir:
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@@ -5688,7 +5688,9 @@ read_partial_die (struct partial_die_inf
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 	    part_die->dirname = DW_STRING (&attr);
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 	  break;
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 	case DW_AT_MIPS_linkage_name:
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-	  part_die->name = DW_STRING (&attr);
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+	  /* Prefer DW_AT_MIPS_linkage_name over DW_AT_name for non-C.  */
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+	  if (cu->language != language_c || part_die->name == NULL)
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+	    part_die->name = DW_STRING (&attr);
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 	  break;
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 	case DW_AT_low_pc:
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 	  has_low_pc_attr = 1;
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@@ -7936,9 +7938,13 @@ dwarf2_linkage_name (struct die_info *di
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 {
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   struct attribute *attr;
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-  attr = dwarf2_attr (die, DW_AT_MIPS_linkage_name, cu);
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-  if (attr && DW_STRING (attr))
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-    return DW_STRING (attr);
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+  /* Prefer DW_AT_MIPS_linkage_name over DW_AT_name for non-C.  */
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+  if (cu->language != language_c)
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+    {
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+      attr = dwarf2_attr (die, DW_AT_MIPS_linkage_name, cu);
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+      if (attr && DW_STRING (attr))
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+	return DW_STRING (attr);
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+    }
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   attr = dwarf2_attr (die, DW_AT_name, cu);
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   if (attr && DW_STRING (attr))
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     return DW_STRING (attr);
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Index: gdb-6.8cvs20080219/gdb/gdbtypes.c
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===================================================================
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--- gdb-6.8cvs20080219.orig/gdb/gdbtypes.c	2008-02-14 23:03:57.000000000 +0100
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+++ gdb-6.8cvs20080219/gdb/gdbtypes.c	2008-02-20 13:35:19.000000000 +0100
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@@ -3106,6 +3106,8 @@ gdbtypes_post_init (struct gdbarch *gdba
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     init_type (TYPE_CODE_INT, 
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 	       gdbarch_int_bit (gdbarch) / TARGET_CHAR_BIT,
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 	       0, "int", (struct objfile *) NULL);
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+  builtin_type->builtin_int_ptr =
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+    make_pointer_type (builtin_type->builtin_int, NULL);
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   builtin_type->builtin_unsigned_int =
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     init_type (TYPE_CODE_INT, 
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 	       gdbarch_int_bit (gdbarch) / TARGET_CHAR_BIT,
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@@ -3215,6 +3217,11 @@ gdbtypes_post_init (struct gdbarch *gdba
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 	       "<text variable, no debug info>", NULL);
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   TYPE_TARGET_TYPE (builtin_type->nodebug_text_symbol) =
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     builtin_type->builtin_int;
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+  builtin_type->nodebug_text_symbol_errno_location =
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+    init_type (TYPE_CODE_FUNC, 1, 0, 
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+	       "<text variable for __errno_location, no debug info>", NULL);
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+  TYPE_TARGET_TYPE (builtin_type->nodebug_text_symbol_errno_location) =
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+    builtin_type->builtin_int_ptr;
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   builtin_type->nodebug_data_symbol =
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     init_type (TYPE_CODE_INT, 
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 	       gdbarch_int_bit (gdbarch) / HOST_CHAR_BIT, 0,
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Index: gdb-6.8cvs20080219/gdb/gdbtypes.h
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===================================================================
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--- gdb-6.8cvs20080219.orig/gdb/gdbtypes.h	2008-02-14 23:03:57.000000000 +0100
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+++ gdb-6.8cvs20080219/gdb/gdbtypes.h	2008-02-20 13:35:19.000000000 +0100
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@@ -942,6 +942,7 @@ struct builtin_type
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   /* Types used for symbols with no debug information.  */
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   struct type *nodebug_text_symbol;
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+  struct type *nodebug_text_symbol_errno_location;
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   struct type *nodebug_data_symbol;
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   struct type *nodebug_unknown_symbol;
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   struct type *nodebug_tls_symbol;
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@@ -960,6 +961,7 @@ struct builtin_type
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   struct type *builtin_char;
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   struct type *builtin_short;
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   struct type *builtin_int;
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+  struct type *builtin_int_ptr;
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   struct type *builtin_long;
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   struct type *builtin_signed_char;
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   struct type *builtin_unsigned_char;
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Index: gdb-6.8cvs20080219/gdb/parse.c
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===================================================================
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--- gdb-6.8cvs20080219.orig/gdb/parse.c	2008-01-02 00:04:03.000000000 +0100
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+++ gdb-6.8cvs20080219/gdb/parse.c	2008-02-20 13:35:19.000000000 +0100
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@@ -437,7 +437,12 @@ write_exp_msymbol (struct minimal_symbol
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     case mst_text:
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     case mst_file_text:
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     case mst_solib_trampoline:
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-      write_exp_elt_type (builtin_type (gdbarch)->nodebug_text_symbol);
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+      if (builtin_type (gdbarch)->nodebug_text_symbol_errno_location != NULL
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+          && strcmp (SYMBOL_LINKAGE_NAME (msymbol), "__errno_location") == 0)
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+	write_exp_elt_type (builtin_type (gdbarch)
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+					  ->nodebug_text_symbol_errno_location);
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+      else
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+	write_exp_elt_type (builtin_type (gdbarch)->nodebug_text_symbol);
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       break;
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     case mst_data:
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Index: gdb-6.8cvs20080219/gdb/target.c
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===================================================================
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--- gdb-6.8cvs20080219.orig/gdb/target.c	2008-02-19 17:22:33.000000000 +0100
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+++ gdb-6.8cvs20080219/gdb/target.c	2008-02-20 13:36:17.000000000 +0100
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@@ -812,6 +812,25 @@ pop_target (void)
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   internal_error (__FILE__, __LINE__, _("failed internal consistency check"));
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 }
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+static int
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+resolve_errno (void *arg)
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+{
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+  CORE_ADDR *arg_addr = arg;
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+  struct expression *expr;
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+  struct cleanup *old_chain = 0;
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+  struct value *val;
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+
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+  expr = parse_expression ("__errno_location()");
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+  old_chain = make_cleanup (free_current_contents, &expr;;
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+  val = evaluate_expression (expr);
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+  *arg_addr = value_as_address (val);
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+  release_value (val);
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+  value_free (val);
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+  do_cleanups (old_chain);
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+
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+  return 1;
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+}
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+
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 /* Using the objfile specified in OBJFILE, find the address for the
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    current thread's thread-local storage with offset OFFSET.  */
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 CORE_ADDR
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@@ -893,7 +912,28 @@ target_translate_tls_address (struct obj
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   /* It wouldn't be wrong here to try a gdbarch method, too; finding
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      TLS is an ABI-specific thing.  But we don't do that yet.  */
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   else
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-    error (_("Cannot find thread-local variables on this target"));
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+    {
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+      struct minimal_symbol *msymbol;
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+
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+      msymbol = lookup_minimal_symbol ("errno", NULL, NULL);
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+      if (msymbol != NULL
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+	  && SYMBOL_VALUE_ADDRESS (msymbol) == offset
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+	  && (SYMBOL_BFD_SECTION (msymbol)->owner == objfile->obfd
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+	      || (objfile->separate_debug_objfile != NULL
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+	          && SYMBOL_BFD_SECTION (msymbol)->owner
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+		     == objfile->separate_debug_objfile->obfd)
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+	      || (objfile->separate_debug_objfile_backlink != NULL
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+	          && SYMBOL_BFD_SECTION (msymbol)->owner
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+		     == objfile->separate_debug_objfile_backlink->obfd)))
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+	{
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+	  if (!catch_errors (resolve_errno, (void *) &addr, "",
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+	                     RETURN_MASK_ALL))
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+	    error (_("TLS symbol `errno' not resolved for non-TLS program."
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+		     "  You should compile the program with `gcc -pthread'."));
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+	}
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+      else
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+	error (_("Cannot find thread-local variables on this target"));
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+    }
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   return addr;
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 }
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Index: gdb-6.8cvs20080219/gdb/testsuite/gdb.dwarf2/dw2-errno.c
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===================================================================
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--- /dev/null	1970-01-01 00:00:00.000000000 +0000
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+++ gdb-6.8cvs20080219/gdb/testsuite/gdb.dwarf2/dw2-errno.c	2008-02-20 13:35:19.000000000 +0100
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@@ -0,0 +1,28 @@
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+/* This testcase is part of GDB, the GNU debugger.
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+
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+   Copyright 2005, 2007 Free Software Foundation, Inc.
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+
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+   This program is free software; you can redistribute it and/or modify
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+   it under the terms of the GNU General Public License as published by
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+   the Free Software Foundation; either version 3 of the License, or
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+   (at your option) any later version.
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+
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+   This program is distributed in the hope that it will be useful,
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+   but WITHOUT ANY WARRANTY; without even the implied warranty of
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+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
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+   GNU General Public License for more details.
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+
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+   You should have received a copy of the GNU General Public License
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+   along with this program.  If not, see <http://www.gnu.org/licenses/>.
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+
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+   Please email any bugs, comments, and/or additions to this file to:
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+   bug-gdb@prep.ai.mit.edu  */
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+
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+#include <errno.h>
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+
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+int main()
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+{
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+  errno = 42;
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+
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+  return 0;	/* breakpoint */
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+}
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Index: gdb-6.8cvs20080219/gdb/testsuite/gdb.dwarf2/dw2-errno.exp
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===================================================================
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--- /dev/null	1970-01-01 00:00:00.000000000 +0000
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+++ gdb-6.8cvs20080219/gdb/testsuite/gdb.dwarf2/dw2-errno.exp	2008-02-20 13:35:19.000000000 +0100
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@@ -0,0 +1,67 @@
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+# Copyright 2007 Free Software Foundation, Inc.
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+
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+# This program is free software; you can redistribute it and/or modify
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+# it under the terms of the GNU General Public License as published by
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+# the Free Software Foundation; either version 3 of the License, or
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+# (at your option) any later version.
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+#
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+# This program is distributed in the hope that it will be useful,
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+# but WITHOUT ANY WARRANTY; without even the implied warranty of
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+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
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+# GNU General Public License for more details.
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+#
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+# You should have received a copy of the GNU General Public License
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+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
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+
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+if $tracelevel then {
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+    strace $tracelevel
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+}
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+
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+set prms_id 0
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+set bug_id 0
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+
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+set testfile dw2-errno
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+set srcfile ${testfile}.c
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+set binfile ${objdir}/${subdir}/${testfile}
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+
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+proc prep {} {
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+    global srcdir subdir binfile
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+    gdb_exit
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+    gdb_start
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+    gdb_reinitialize_dir $srcdir/$subdir
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+    gdb_load ${binfile}
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+
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+    runto_main
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+
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+    gdb_breakpoint [gdb_get_line_number "breakpoint"]
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+    gdb_continue_to_breakpoint "breakpoint"
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+}
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+
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+if  { [gdb_compile "${srcdir}/${subdir}/${srcfile}" "${binfile}" executable "additional_flags=-g2"] != "" } {
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+    untested "Couldn't compile test program"
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+    return -1
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+}
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+prep
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+gdb_test "print errno" ".* = 42" "errno with macros=N threads=N"
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+
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+if  { [gdb_compile "${srcdir}/${subdir}/${srcfile}" "${binfile}" executable "additional_flags=-g3"] != "" } {
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+    untested "Couldn't compile test program"
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+    return -1
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+}
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+prep
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+gdb_test "print errno" ".* = 42" "errno with macros=Y threads=N"
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+
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+if {[gdb_compile_pthreads "${srcdir}/${subdir}/${srcfile}" "${binfile}" executable "additional_flags=-g2"] != "" } {
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+    return -1
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+}
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+prep
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+gdb_test "print errno" ".* = 42" "errno with macros=N threads=Y"
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+
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+if {[gdb_compile_pthreads "${srcdir}/${subdir}/${srcfile}" "${binfile}" executable "additional_flags=-g3"] != "" } {
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+    return -1
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+}
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+prep
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+gdb_test "print errno" ".* = 42" "errno with macros=Y threads=Y"
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+
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+# TODO: Test the error on resolving ERRNO with only libc loaded.
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+# Just how to find the current libc filename?