http://sourceware.org/ml/gdb-patches/2016-10/msg00207.html
Subject: [patch+7.12.1 2/2] Fix TLS (such as 'errno') regression


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Hi,

2273f0ac95a79ce29ef42025c63f90e82cf907d7 is the first bad commit
commit 2273f0ac95a79ce29ef42025c63f90e82cf907d7
Author: Tom Tromey <tromey@redhat.com>
Date:   Tue Oct 15 13:28:57 2013 -0600
    change minsyms not to be relocated at read-time
[FYI v3 06/10] change minsyms not to be relocated at read-time
Message-Id: <1393441273-32268-7-git-send-email-tromey@redhat.com>
https://sourceware.org/ml/gdb-patches/2014-02/msg00798.html

mv /usr/lib/debug /usr/lib/debug-x
echo 'int main(){}'|gcc -pthread -x c -
./gdb -q -ex start -ex 'set debug expr 1' -ex 'p errno' ./a.out 
	    0  UNOP_MEMVAL_TLS       TLS type @0x35df7e0 (__thread /* "/lib64/libc.so.6" */ <thread local variable, no debug info>)
	    4    OP_LONG               Type @0x35df850 (__CORE_ADDR), value 140737345728528 (0x7ffff77fb010)
Cannot access memory at address 0xffffef7c9698
->
	    0  UNOP_MEMVAL_TLS       TLS type @0x3ad9520 (__thread /* "/lib64/libc.so.6" */ <thread local variable, no debug info>)
	    4    OP_LONG               Type @0x3ad9590 (__CORE_ADDR), value 16 (0x10)
$1 = 0

With glibc debuginfo, that is without: mv /usr/lib/debug /usr/lib/debug-x
	    0  OP_VAR_VALUE          Block @0x3b30e70, symbol @0x3b30d10 (errno)
$1 = 0
So such case is unrelated to this patch and the regression is not visible with
glibc debuginfo installed.

I guess all these issues will be solved by Gary Benson's Infinity.
But at least for older non-Infinity glibcs GDB should not regress.

For the testcase it is important the variable is in objfile with non-zero base
address.  glibc is a shared library for 'errno' but I found easier for the
testcase to use PIE instead of a shlib.  For TLS variables in PT_EXEC the
regression obviously does not happen.

It has been found by a more complete testcase present in Fedora, the fix there
also solves more cases where FSF GDB currently cannot resolve 'errno':
	http://pkgs.fedoraproject.org/cgit/rpms/gdb.git/tree/gdb-6.5-bz185337-resolve-tls-without-debuginfo-v2.patch
	FAIL: gdb.dwarf2/dw2-errno2.exp: macros=N threads=Y: print errno for core

No regressions on {x86_64,x86_64-m32,i686}-fedora26pre-linux-gnu.

OK for check-in?


Thanks,
Jan

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gdb/ChangeLog
2016-10-09  Jan Kratochvil  <jan.kratochvil@redhat.com>

	* parse.c (write_exp_msymbol): Fix ADDR computation.

gdb/testsuite/ChangeLog
2016-10-09  Jan Kratochvil  <jan.kratochvil@redhat.com>

	* gdb.threads/tls-nodebug-pie.c: New file.
	* gdb.threads/tls-nodebug-pie.exp: New file.

--- a/gdb/parse.c
+++ b/gdb/parse.c
@@ -480,13 +480,17 @@ write_exp_msymbol (struct parser_state *ps,
   struct objfile *objfile = bound_msym.objfile;
   struct gdbarch *gdbarch = get_objfile_arch (objfile);
 
-  CORE_ADDR addr = BMSYMBOL_VALUE_ADDRESS (bound_msym);
   struct obj_section *section = MSYMBOL_OBJ_SECTION (objfile, msymbol);
   enum minimal_symbol_type type = MSYMBOL_TYPE (msymbol);
-  CORE_ADDR pc;
+  CORE_ADDR addr, pc;
   const int is_tls = (section != NULL
 		      && section->the_bfd_section->flags & SEC_THREAD_LOCAL);
 
+  if (is_tls)
+    addr = MSYMBOL_VALUE_RAW_ADDRESS (bound_msym.minsym);
+  else
+    addr = BMSYMBOL_VALUE_ADDRESS (bound_msym);
+
   /* The minimal symbol might point to a function descriptor;
      resolve it to the actual code address instead.  */
   pc = gdbarch_convert_from_func_ptr_addr (gdbarch, addr, &current_target);
--- /dev/null
+++ b/gdb/testsuite/gdb.threads/tls-nodebug-pie.c
@@ -0,0 +1,27 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2016 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 <pthread.h>
+
+__thread int thread_local = 42;
+
+int main(void)
+{
+  /* Ensure we link against pthreads even with --as-needed.  */
+  pthread_testcancel();
+  return 0;
+}
--- /dev/null
+++ b/gdb/testsuite/gdb.threads/tls-nodebug-pie.exp
@@ -0,0 +1,29 @@
+# Copyright 2016 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/>.
+
+standard_testfile
+
+if {[gdb_compile_pthreads "${srcdir}/${subdir}/${srcfile}" "${binfile}" executable \
+			  [list "additional_flags=-fPIE -pie"]] != "" } {
+    return -1
+}
+
+clean_restart ${binfile}
+if ![runto_main] then {
+   return 0
+}
+
+# Formerly: Cannot access memory at address 0xd5554d5216fc
+gdb_test "p thread_local" " = 42" "thread local storage"

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