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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