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

2008-02-24  Jan Kratochvil  <jan.kratochvil@redhat.com>

	Port to GDB-6.8pre.

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.

Original patch hooked into target_translate_tls_address.  But its inferior
call invalidates `struct frame *' in the callers - RH BZ 690908.


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

--- a/gdb/printcmd.c
+++ b/gdb/printcmd.c
@@ -967,6 +967,8 @@ print_command_1 (char *exp, int inspect, int voidprint)
 
   if (exp && *exp)
     {
+      if (strcmp (exp, "errno") == 0)
+	exp = "*((int *(*) (void)) __errno_location) ()";
       expr = parse_expression (exp);
       old_chain = make_cleanup (free_current_contents, &expr);
       cleanup = 1;
Index: gdb-7.2/gdb/testsuite/gdb.dwarf2/dw2-errno.c
===================================================================
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ gdb-7.2/gdb/testsuite/gdb.dwarf2/dw2-errno.c	2011-03-29 10:55:35.000000000 +0200
@@ -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 */
+}
Index: gdb-7.2/gdb/testsuite/gdb.dwarf2/dw2-errno.exp
===================================================================
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ gdb-7.2/gdb/testsuite/gdb.dwarf2/dw2-errno.exp	2011-03-29 10:55:35.000000000 +0200
@@ -0,0 +1,60 @@
+# 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/>.
+
+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?