Fix debugging of stripped PIE executables with padded PT_TLS

Certain PIE executables produced by gold cannot be debugged by gdb after
being stripped. GDB requires program headers of PIE executables to match,
and those checks may fail due to adjustments made during stripping.

One case of this occurs because strip recomputes the memsz of PT_TLS and
does not add alignment, while gold does. This is another variant of PR
11786, so apply the same fix of relaxing the program header matching.

gdb/ChangeLog:

	PR gdb/11786
	* solib-svr4.c (svr4_exec_displacement): Ignore memsz fields
	for PT_TLS segments.

gdb/testsuite/ChangeLog:

	PR gdb/11786
	* gdb.base/gcore-tls-pie.c: New file.
	* gdb.base/gcore-tls-pie.exp: New file.

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index c75c0e14191109a4d07b3aa097ed1a419ab873d6..cb87cee4e72a48ff3c7ebc8d43bc144e2b523acb 100644 (file)
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,9 @@
+2018-08-19  Michael Spang  <spang@google.com>
+
+       PR gdb/11786
+       * solib-svr4.c (svr4_exec_displacement): Ignore memsz fields
+       for PT_TLS segments.
+
 2018-08-18  Kevin Buettner  <kevinb@redhat.com>
 
        * dwarf2expr.h (struct dwarf_expr_context): Add virtual method

diff --git a/gdb/solib-svr4.c b/gdb/solib-svr4.c
index 6f48c6863209dcd23c50177eba1277e5d5d7b686..84589509ef9f48c150efe34f650c01d1b86ce5c0 100644 (file)
--- a/gdb/solib-svr4.c
+++ b/gdb/solib-svr4.c
@@ -2709,8 +2709,10 @@ svr4_exec_displacement (CORE_ADDR *displacementp)
 
                  /* Strip modifies the flags and alignment of PT_GNU_RELRO.
                     CentOS-5 has problems with filesz, memsz as well.
+                    Strip also modifies memsz of PT_TLS.
                     See PR 11786.  */
-                 if (phdr2[i].p_type == PT_GNU_RELRO)
+                 if (phdr2[i].p_type == PT_GNU_RELRO ||
+                     phdr2[i].p_type == PT_TLS)
                    {
                      Elf32_External_Phdr tmp_phdr = *phdrp;
                      Elf32_External_Phdr tmp_phdr2 = *phdr2p;
@@ -2840,8 +2842,10 @@ svr4_exec_displacement (CORE_ADDR *displacementp)
 
                  /* Strip modifies the flags and alignment of PT_GNU_RELRO.
                     CentOS-5 has problems with filesz, memsz as well.
+                    Strip also modifies memsz of PT_TLS.
                     See PR 11786.  */
-                 if (phdr2[i].p_type == PT_GNU_RELRO)
+                 if (phdr2[i].p_type == PT_GNU_RELRO ||
+                     phdr2[i].p_type == PT_TLS)
                    {
                      Elf64_External_Phdr tmp_phdr = *phdrp;
                      Elf64_External_Phdr tmp_phdr2 = *phdr2p;

diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index b70db16eb0eae5dcf2863921acf626dff2998a17..bdef4be4bb979a7077993ff3ec26d5c36f3025ab 100644 (file)
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,3 +1,9 @@
+2018-08-19  Michael Spang  <spang@google.com>
+
+       PR gdb/11786
+       * gdb.base/gcore-tls-pie.c: New file.
+       * gdb.base/gcore-tls-pie.exp: New file.
+
 2018-08-18  Kevin Buettner  <kevinb@redhat.com>
 
        * lib/dwarf.exp: Add support for DW_OP_GNU_variable_value.

diff --git a/gdb/testsuite/gdb.base/gcore-tls-pie.c b/gdb/testsuite/gdb.base/gcore-tls-pie.c
new file mode 100644 (file)
index 0000000..aaba20f
--- /dev/null
+++ b/gdb/testsuite/gdb.base/gcore-tls-pie.c
@@ -0,0 +1,48 @@
+/* Copyright 2013-2018 Free Software Foundation, Inc.
+
+   This file is part of GDB.
+
+   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/>.  */
+
+/* The size of these variables is chosen so that gold will add some padding
+   to the TLS program header (total size of 16 bytes on x86_64) which strip
+   will remove (bringing it down to 9 bytes).  */
+
+__thread long j;
+__thread char i;
+
+void
+break_here (void)
+{
+  *(int *) 0 = 0;
+}
+
+void
+foo (void)
+{
+  break_here ();
+}
+
+void
+bar (void)
+{
+  foo ();
+}
+
+int
+main (void)
+{
+  bar ();
+  return 0;
+}

diff --git a/gdb/testsuite/gdb.base/gcore-tls-pie.exp b/gdb/testsuite/gdb.base/gcore-tls-pie.exp
new file mode 100644 (file)
index 0000000..1f7381e
--- /dev/null
+++ b/gdb/testsuite/gdb.base/gcore-tls-pie.exp
@@ -0,0 +1,62 @@
+# Copyright 2013-2018 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/>.
+
+# PR 11786 (Gold and strip differ on memsz field of PT_TLS).
+# Generate a core file from the stripped version of the program,
+# and then try to debug the core with the unstripped version.
+
+standard_testfile
+
+if {[prepare_for_testing "failed to prepare" $testfile $srcfile {debug additional_flags=-fpie "ldflags=-pie -fuse-ld=gold"}]} {
+    return -1
+}
+
+set stripped_binfile ${binfile}.stripped
+set gcorefile ${binfile}.gcore
+
+set strip_program [transform strip]
+remote_file host delete ${stripped_binfile}
+if [run_on_host "strip" "$strip_program" "-g -o ${stripped_binfile} $binfile"] {
+    return -1
+}
+
+# Workaround PR binutils/10802:
+# Preserve the 'x' bit also for PIEs (Position Independent Executables).
+set perm [file attributes ${binfile} -permissions]
+file attributes ${stripped_binfile} -permissions $perm
+
+clean_restart ${stripped_binfile}
+
+# The binary is stripped of debug info, but not minsyms.
+if ![runto break_here] {
+    fail "can't run to break_here"
+    return -1
+}
+
+if {![gdb_gcore_cmd $gcorefile "save a corefile"]} {
+    return -1
+}
+
+# Now restart gdb with the unstripped binary and load the corefile.
+
+clean_restart ${binfile}
+
+gdb_test "core ${gcorefile}" \
+    "Core was generated by .*" "re-load generated corefile"
+
+# Put $pc in gdb.log for debug purposes for comparison with stripped case.
+gdb_test "x/i \$pc" "break_here.*"
+
+gdb_test "frame" "#0 \[^\r\n\]* break_here .*" "unstripped + core ok"