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http://sourceware.org/ml/gdb-patches/2016-10/msg00207.html
Subject: [patch+7.12.1 2/2] Fix TLS (such as 'errno') regression
--3Pql8miugIZX0722
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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
--3Pql8miugIZX0722
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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"
--3Pql8miugIZX0722--
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