https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=185337

currently for trivial nonthreaded helloworld with no debug info up to -ggdb2 you

will get:

        (gdb) p errno

        [some error]

* with -ggdb2 and less "errno" in fact does not exist anywhere as it was

  compiled to "(*__errno_location ())" and the macro definition is not present.

  Unfortunately gdb will find the TLS symbol and it will try to access it but

  as the program has been compiled without -lpthread the TLS base register

  (%gs on i386) is not setup and it will result in:

        Cannot access memory at address 0x8

Attached suggestion patch how to deal with the most common "errno" symbol

for the most common under-ggdb3 compiled programs.

2007-11-03  Jan Kratochvil  <jan.kratochvil@redhat.com>

	* ./gdb/dwarf2read.c (read_partial_die, dwarf2_linkage_name): Prefer

	DW_AT_MIPS_linkage_name over DW_AT_name now only for non-C.

glibc-debuginfo-2.7-2.x86_64: /usr/lib/debug/lib64/libc.so.6.debug:

  <81a2>     DW_AT_name        : (indirect string, offset: 0x280e): __errno_location

  <81a8>     DW_AT_MIPS_linkage_name: (indirect string, offset: 0x2808): *__GI___errno_location

--- ./gdb/dwarf2read.c	25 Oct 2007 20:54:27 -0000	1.236

+++ ./gdb/dwarf2read.c	3 Nov 2007 21:03:43 -0000

@@ -5550,8 +5550,8 @@ read_partial_die (struct partial_die_inf

 	{

 	case DW_AT_name:

-	  /* Prefer DW_AT_MIPS_linkage_name over DW_AT_name.  */

-	  if (part_die->name == NULL)

+	  /* Prefer DW_AT_MIPS_linkage_name over DW_AT_name for non-C.  */

+	  if (cu->language == language_c || part_die->name == NULL)

 	    part_die->name = DW_STRING (&attr);

 	  break;

 	case DW_AT_comp_dir:

@@ -5559,7 +5559,9 @@ read_partial_die (struct partial_die_inf

 	    part_die->dirname = DW_STRING (&attr);

 	  break;

 	case DW_AT_MIPS_linkage_name:

-	  part_die->name = DW_STRING (&attr);

+	  /* Prefer DW_AT_MIPS_linkage_name over DW_AT_name for non-C.  */

+	  if (cu->language != language_c || part_die->name == NULL)

+	    part_die->name = DW_STRING (&attr);

 	  break;

 	case DW_AT_low_pc:

 	  has_low_pc_attr = 1;

@@ -7871,9 +7873,13 @@ dwarf2_linkage_name (struct die_info *di

 {

   struct attribute *attr;

-  attr = dwarf2_attr (die, DW_AT_MIPS_linkage_name, cu);

-  if (attr && DW_STRING (attr))

-    return DW_STRING (attr);

+  /* Prefer DW_AT_MIPS_linkage_name over DW_AT_name for non-C.  */

+  if (cu->language != language_c)

+    {

+      attr = dwarf2_attr (die, DW_AT_MIPS_linkage_name, cu);

+      if (attr && DW_STRING (attr))

+	return DW_STRING (attr);

+    }

   attr = dwarf2_attr (die, DW_AT_name, cu);

   if (attr && DW_STRING (attr))

     return DW_STRING (attr);

diff -u -X /home/jkratoch/.diffi.list -rup gdb-6.7.1/gdb/gdbtypes.c gdb-6.7.1-patched/gdb/gdbtypes.c

--- gdb-6.7.1/gdb/gdbtypes.c	2007-11-04 01:43:03.000000000 +0100

+++ gdb-6.7.1-patched/gdb/gdbtypes.c	2007-11-04 01:09:31.000000000 +0100

@@ -3465,6 +3465,8 @@ gdbtypes_post_init (struct gdbarch *gdba

     init_type (TYPE_CODE_INT, 

 	       gdbarch_int_bit (current_gdbarch) / TARGET_CHAR_BIT,

 	       0, "int", (struct objfile *) NULL);

+  builtin_type->builtin_int_ptr =

+    make_pointer_type (builtin_type->builtin_int, NULL);

   builtin_type->builtin_unsigned_int =

     init_type (TYPE_CODE_INT, 

 	       gdbarch_int_bit (current_gdbarch) / TARGET_CHAR_BIT,

@@ -3559,6 +3561,11 @@ gdbtypes_post_init (struct gdbarch *gdba

 	       "<text variable, no debug info>", NULL);

   TYPE_TARGET_TYPE (builtin_type->nodebug_text_symbol) =

     builtin_type->builtin_int;

+  builtin_type->nodebug_text_symbol_errno_location =

+    init_type (TYPE_CODE_FUNC, 1, 0, 

+	       "<text variable for __errno_location, no debug info>", NULL);

+  TYPE_TARGET_TYPE (builtin_type->nodebug_text_symbol_errno_location) =

+    builtin_type->builtin_int_ptr;

   builtin_type->nodebug_data_symbol =

     init_type (TYPE_CODE_INT, 

 	       gdbarch_int_bit (gdbarch) / HOST_CHAR_BIT, 0,

diff -u -X /home/jkratoch/.diffi.list -rup gdb-6.7.1/gdb/gdbtypes.h gdb-6.7.1-patched/gdb/gdbtypes.h

--- gdb-6.7.1/gdb/gdbtypes.h	2007-11-04 01:43:03.000000000 +0100

+++ gdb-6.7.1-patched/gdb/gdbtypes.h	2007-11-04 01:07:50.000000000 +0100

@@ -1008,6 +1008,7 @@ struct builtin_type

   /* Types used for symbols with no debug information.  */

   struct type *nodebug_text_symbol;

+  struct type *nodebug_text_symbol_errno_location;

   struct type *nodebug_data_symbol;

   struct type *nodebug_unknown_symbol;

   struct type *nodebug_tls_symbol;

@@ -1026,6 +1027,7 @@ struct builtin_type

   struct type *builtin_char;

   struct type *builtin_short;

   struct type *builtin_int;

+  struct type *builtin_int_ptr;

   struct type *builtin_long;

   struct type *builtin_signed_char;

   struct type *builtin_unsigned_char;

diff -u -X /home/jkratoch/.diffi.list -rup gdb-6.7.1/gdb/parse.c gdb-6.7.1-patched/gdb/parse.c

--- gdb-6.7.1/gdb/parse.c	2007-08-23 20:08:36.000000000 +0200

+++ gdb-6.7.1-patched/gdb/parse.c	2007-11-04 01:06:59.000000000 +0100

@@ -424,7 +424,12 @@ write_exp_msymbol (struct minimal_symbol

     case mst_text:

     case mst_file_text:

     case mst_solib_trampoline:

-      write_exp_elt_type (builtin_type (gdbarch)->nodebug_text_symbol);

+      if (builtin_type (gdbarch)->nodebug_text_symbol_errno_location != NULL

+          && strcmp (SYMBOL_LINKAGE_NAME (msymbol), "__errno_location") == 0)

+	write_exp_elt_type (builtin_type (gdbarch)

+					  ->nodebug_text_symbol_errno_location);

+      else

+	write_exp_elt_type (builtin_type (gdbarch)->nodebug_text_symbol);

       break;

     case mst_data:

diff -u -X /home/jkratoch/.diffi.list -rup gdb-6.7.1/gdb/target.c gdb-6.7.1-patched/gdb/target.c

--- gdb-6.7.1/gdb/target.c	2007-11-04 01:43:03.000000000 +0100

+++ gdb-6.7.1-patched/gdb/target.c	2007-11-04 01:37:45.000000000 +0100

@@ -819,6 +819,25 @@ pop_target (void)

   internal_error (__FILE__, __LINE__, _("failed internal consistency check"));

 }

+static int

+resolve_errno (void *arg)

+{

+  CORE_ADDR *arg_addr = arg;

+  struct expression *expr;

+  struct cleanup *old_chain = 0;

+  struct value *val;

+

+  expr = parse_expression ("__errno_location()");

+  old_chain = make_cleanup (free_current_contents, &expr;;

+  val = evaluate_expression (expr);

+  *arg_addr = value_as_address (val);

+  release_value (val);

+  value_free (val);

+  do_cleanups (old_chain);

+

+  return 1;

+}

+

 /* Using the objfile specified in BATON, find the address for the

    current thread's thread-local storage with offset OFFSET.  */

 CORE_ADDR

@@ -906,7 +925,22 @@ target_translate_tls_address (struct obj

   /* It wouldn't be wrong here to try a gdbarch method, too; finding

      TLS is an ABI-specific thing.  But we don't do that yet.  */

   else

-    error (_("Cannot find thread-local variables on this target"));

+    {

+      struct minimal_symbol *msymbol;

+

+      msymbol = lookup_minimal_symbol ("errno", NULL, NULL);

+      if (msymbol != NULL

+	  && SYMBOL_VALUE_ADDRESS (msymbol) == offset

+	  && SYMBOL_BFD_SECTION (msymbol)->owner == objfile->obfd)

+	{

+	  if (!catch_errors (resolve_errno, (void *) &addr, "",

+	                     RETURN_MASK_ALL))

+	    error (_("TLS symbol `errno' not resolved for non-TLS program."

+		     "  You should compile the program with `gcc -pthread'."));

+	}

+      else

+	error (_("Cannot find thread-local variables on this target"));

+    }

   return addr;

 }

diff -u -X /home/jkratoch/.diffi.list -rup gdb-6.7.1/gdb/testsuite/gdb.dwarf2/dw2-errno.c gdb-6.7.1-patched/gdb/testsuite/gdb.dwarf2/dw2-errno.c

--- gdb-6.7.1/gdb/testsuite/gdb.dwarf2/dw2-errno.c	2007-11-04 01:43:41.000000000 +0100

+++ gdb-6.7.1-patched/gdb/testsuite/gdb.dwarf2/dw2-errno.c	2007-11-03 23:29:02.000000000 +0100

@@ -0,0 +1,28 @@

+/* This testcase is part of GDB, the GNU debugger.

+

+   Copyright 2005, 2007 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/>.

+

+   Please email any bugs, comments, and/or additions to this file to:

+   bug-gdb@prep.ai.mit.edu  */

+

+#include <errno.h>

+

+int main()

+{

+  errno = 42;

+

+  return 0;	/* breakpoint */

+}

diff -u -X /home/jkratoch/.diffi.list -rup gdb-6.7.1/gdb/testsuite/gdb.dwarf2/dw2-errno.exp gdb-6.7.1-patched/gdb/testsuite/gdb.dwarf2/dw2-errno.exp

--- gdb-6.7.1/gdb/testsuite/gdb.dwarf2/dw2-errno.exp	2007-11-04 01:43:39.000000000 +0100

+++ gdb-6.7.1-patched/gdb/testsuite/gdb.dwarf2/dw2-errno.exp	2007-11-04 01:41:46.000000000 +0100

@@ -0,0 +1,67 @@

+# Copyright 2007 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/>.

+

+if $tracelevel then {

+    strace $tracelevel

+}

+

+set prms_id 0

+set bug_id 0

+

+set testfile dw2-errno

+set srcfile ${testfile}.c

+set binfile ${objdir}/${subdir}/${testfile}

+

+proc prep {} {

+    global srcdir subdir binfile

+    gdb_exit

+    gdb_start

+    gdb_reinitialize_dir $srcdir/$subdir

+    gdb_load ${binfile}

+

+    runto_main

+

+    gdb_breakpoint [gdb_get_line_number "breakpoint"]

+    gdb_continue_to_breakpoint "breakpoint"

+}

+

+if  { [gdb_compile "${srcdir}/${subdir}/${srcfile}" "${binfile}" executable "additional_flags=-g2"] != "" } {

+    untested "Couldn't compile test program"

+    return -1

+}

+prep

+gdb_test "print errno" ".* = 42" "errno with macros=N threads=N"

+

+if  { [gdb_compile "${srcdir}/${subdir}/${srcfile}" "${binfile}" executable "additional_flags=-g3"] != "" } {

+    untested "Couldn't compile test program"

+    return -1

+}

+prep

+gdb_test "print errno" ".* = 42" "errno with macros=Y threads=N"

+

+if {[gdb_compile_pthreads "${srcdir}/${subdir}/${srcfile}" "${binfile}" executable "additional_flags=-g2"] != "" } {

+    return -1

+}

+prep

+gdb_test "print errno" ".* = 42" "errno with macros=N threads=Y"

+

+if {[gdb_compile_pthreads "${srcdir}/${subdir}/${srcfile}" "${binfile}" executable "additional_flags=-g3"] != "" } {

+    return -1

+}

+prep

+gdb_test "print errno" ".* = 42" "errno with macros=Y threads=Y"

+

+# TODO: Test the error on resolving ERRNO with only libc loaded.

+# Just how to find the current libc filename?