[binutils-gdb] Fix accessing TLS variables with no debug info

[Pedro Alves <palves at sourceware dot org>]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=fbd1b77155bd8139033b72871dbe7bf5be6031b1

commit fbd1b77155bd8139033b72871dbe7bf5be6031b1
Author: Jan Kratochvil <jan.kratochvil@redhat.com>
Date:   Wed Sep 6 12:32:46 2017 +0100

    Fix accessing TLS variables with no debug info
    
    Since 2273f0ac95a7 ("change minsyms not to be relocated at
    read-time"), printing TLS symbols of objfiles with a non-zero base
    address, without debug info, fails.
    
    E.g., with:
    
     $ mv /usr/lib/debug /usr/lib/debug-x
    
    to get debug info out of the way, we get:
    
     $ echo 'int main(){}' | gcc -pthread -x c -
     $ ./gdb -q -ex start -ex 'p (int) errno' ./a.out
     Cannot access memory at address 0xffffef7c0698
    
    instead of the expected:
    
     $1 = 0
    
    The regression is not visible with glibc debuginfo installed.
    
    The problem is that we compute the address of TLS minsyms incorrectly.
    
    To trigger the problem, it is important that the variable is in an
    objfile with a non-zero base address.  While glibc is a shared library
    for 'errno', it's easier for the testcase to use PIE instead of a
    shlib.  For TLS variables in PT_EXEC the regression obviously does not
    happen.
    
    gdb/ChangeLog
    2017-09-06  Jan Kratochvil  <jan.kratochvil@redhat.com>
    
    	* parse.c (find_minsym_type_and_address): Don't relocate addresses
    	of TLS symbols.
    
    gdb/testsuite/ChangeLog
    2017-09-06  Jan Kratochvil  <jan.kratochvil@redhat.com>
    
    	* gdb.threads/tls-nodebug-pie.c: New file.
    	* gdb.threads/tls-nodebug-pie.exp: New file.

Diff:
---
 gdb/ChangeLog                                 |  5 +++++
 gdb/parse.c                                   | 12 +++++++++--
 gdb/testsuite/ChangeLog                       |  5 +++++
 gdb/testsuite/gdb.threads/tls-nodebug-pie.c   | 28 ++++++++++++++++++++++++++
 gdb/testsuite/gdb.threads/tls-nodebug-pie.exp | 29 +++++++++++++++++++++++++++
 5 files changed, 77 insertions(+), 2 deletions(-)

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 6d2eae5..ee15c60 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,8 @@
+2017-09-06  Jan Kratochvil  <jan.kratochvil@redhat.com>
+
+	* parse.c (find_minsym_type_and_address): Don't relocate addresses
+	of TLS symbols.
+
 2017-09-05  Philippe Waroquiers  <philippe.waroquiers@skynet.be>
 
 	* objfiles.c (get_objfile_bfd_data): Remove useless obstack_init
diff --git a/gdb/parse.c b/gdb/parse.c
index 7971f6c..a11689b 100644
--- a/gdb/parse.c
+++ b/gdb/parse.c
@@ -491,11 +491,19 @@ find_minsym_type_and_address (minimal_symbol *msymbol,
 {
   bound_minimal_symbol bound_msym = {msymbol, 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;
 
+  bool is_tls = (section != NULL
+		 && section->the_bfd_section->flags & SEC_THREAD_LOCAL);
+
+  /* Addresses of TLS symbols are really offsets into a
+     per-objfile/per-thread storage block.  */
+  CORE_ADDR addr = (is_tls
+		    ? MSYMBOL_VALUE_RAW_ADDRESS (bound_msym.minsym)
+		    : 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);
@@ -525,7 +533,7 @@ find_minsym_type_and_address (minimal_symbol *msymbol,
   if (overlay_debugging)
     addr = symbol_overlayed_address (addr, section);
 
-  if (section && section->the_bfd_section->flags & SEC_THREAD_LOCAL)
+  if (is_tls)
     {
       /* Skip translation if caller does not need the address.  */
       if (address_p != NULL)
diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index b3bed5c..3f64c6c 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2017-09-06  Jan Kratochvil  <jan.kratochvil@redhat.com>
+
+	* gdb.threads/tls-nodebug-pie.c: New file.
+	* gdb.threads/tls-nodebug-pie.exp: New file.
+
 2017-09-05  Tom Tromey  <tom@tromey.com>
 
 	* lib/gdb.exp (gdb_compile): Don't use universal_compile_options
diff --git a/gdb/testsuite/gdb.threads/tls-nodebug-pie.c b/gdb/testsuite/gdb.threads/tls-nodebug-pie.c
new file mode 100644
index 0000000..c2f62f2
--- /dev/null
+++ b/gdb/testsuite/gdb.threads/tls-nodebug-pie.c
@@ -0,0 +1,28 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2016-2017 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;
+}
diff --git a/gdb/testsuite/gdb.threads/tls-nodebug-pie.exp b/gdb/testsuite/gdb.threads/tls-nodebug-pie.exp
new file mode 100644
index 0000000..ca384a0
--- /dev/null
+++ b/gdb/testsuite/gdb.threads/tls-nodebug-pie.exp
@@ -0,0 +1,29 @@
+# Copyright 2016-2017 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 0xffffef7c0698
+gdb_test "p (int) thread_local" " = 42" "thread local storage"