[BZ,#17075] ARM: Fix immediate calculation of R_ARM_TLS_DESC
Commit Message
Hello,
I've noticed external symbol value calculation made in the dynamic linker
while processing the R_ARM_TLS_DESC reloc in the immediately-bound case is
broken. To figure out the final value of the symbol the calculation makes
use of the descriptor's argument that in this case is set to the symbol's
table index in the symbol table ORed with 0x80000000 and adds it to the
actual value of the symbol resolved by the linker.
Such calculated value is then used if the static specialisation is
selected and the typical result is a segfault. This is easily reproduced
by trying any program that has (or whose link-time dependency has)
R_ARM_TLS_DESC relocs against external symbols and running it with
$LD_BIND_NOW set to 1 in the environment.
Such calculation is plain wrong and in the case of an external symbol the
value of the descriptor's argument provided by the static linker can be
simply discarded as it's only needed by the lazy specialisation to resolve
the symbol (that in this case already has been).
This is addressed with the patch below. A test case is included. It has
been verified across a number multilibs, all failing the test case before
and passing after the fix has been applied. No regressions, but one'd
expect that for such a localised change.
It is worth noting that it is imperative that the $LD_BIND_NOW setting is
used, it is not enough to link the test case's executable and dynamic
module with `-Wl,-z,now'. It may mean that the DT_BIND_NOW dynamic tag
the `-z now' static linker's option produces is not respected for some
reason, but I haven't investigated it further.
The test case required extra `configure' scriptery, because older
versions of GCC do not support TLS descriptors or the `-mtls-dialect='
option. Additionally GCC does not validate binutils' support for TLS
decriptors at the build time, so modern GCC built with the effective
configuration of `--with-tls=gnu' will still work with older binutils and
accept the `-mtls-dialect=gnu2' option, but the assembler will then choke
on the lack of support for the syntax used to produce TLS descriptor
relocations if any code is produced that requests them. Therefore the
`configure' test uses a piece of inline assembly that explicitly requests
a TLS descriptor relocation on a symbol and is guaranteed to break with
older binutils. Consequently both GCC and binutils support is verified
with a single `configure' test.
OK to apply?
2014-06-19 Maciej W. Rozycki <macro@codesourcery.com>
[BZ #17075]
* sysdeps/arm/dl-machine.h (elf_machine_rel) <R_ARM_TLS_DESC>:
Fix calculation of the symbol's value.
* sysdeps/arm/tst-armtlsdesc.c: New file.
* sysdeps/arm/tst-armtlsdescmod.c: New file
* sysdeps/arm/Makefile (tests): Add `tst-armtlsdesc'.
(modules-names): Add `tst-armtlsdescmod'.
(CFLAGS-tst-armtlsdescmod.c, tst-armtlsdesc-ENV): New variables.
($(objpfx)tst-armtlsdesc): New dependency.
* sysdeps/arm/configure.ac: Add a check for tools' GNU descriptor
TLS scheme support.
* config.make.in (have-arm-tls-desc): New variable.
* configure.ac: Handle it.
* sysdeps/arm/configure: Regenerate.
* configure: Regenerate.
Maciej
glibc-arm-tls-desc-imm.diff
Comments
On Thu, 19 Jun 2014, Maciej W. Rozycki wrote:
> * config.make.in (have-arm-tls-desc): New variable.
> * configure.ac: Handle it.
You shouldn't need these changes to architecture-independent files. Try
using the LIBC_CONFIG_VAR macro from aclocal.m4 instead.
On Thu, Jun 19, 2014 at 11:29:44PM +0100, Maciej W. Rozycki wrote:
> Index: glibc-fsf-trunk-quilt/sysdeps/arm/dl-machine.h
> ===================================================================
> --- glibc-fsf-trunk-quilt.orig/sysdeps/arm/dl-machine.h 2014-06-19 22:24:23.731968218 +0100
> +++ glibc-fsf-trunk-quilt/sysdeps/arm/dl-machine.h 2014-06-19 22:25:06.741661376 +0100
> @@ -452,7 +452,10 @@ elf_machine_rel (struct link_map *map, c
> else
> # endif
> {
> - value = sym->st_value + td->argument.value;
> + if (td->argument.value & 0x80000000)
> + value = sym->st_value;
> + else
> + value = td->argument.value;
Can you explain why sym->st_value is completely ignored in the else
case? My understanding is that (aside from the high-bit-set condition
you found) td->argument.value is semantically an addend; I certainly
don't see any way it could already contain the desired symbol value
(offset).
Rich
On Fri, 20 Jun 2014, Rich Felker wrote:
> > Index: glibc-fsf-trunk-quilt/sysdeps/arm/dl-machine.h
> > ===================================================================
> > --- glibc-fsf-trunk-quilt.orig/sysdeps/arm/dl-machine.h 2014-06-19 22:24:23.731968218 +0100
> > +++ glibc-fsf-trunk-quilt/sysdeps/arm/dl-machine.h 2014-06-19 22:25:06.741661376 +0100
> > @@ -452,7 +452,10 @@ elf_machine_rel (struct link_map *map, c
> > else
> > # endif
> > {
> > - value = sym->st_value + td->argument.value;
> > + if (td->argument.value & 0x80000000)
> > + value = sym->st_value;
> > + else
> > + value = td->argument.value;
>
> Can you explain why sym->st_value is completely ignored in the else
> case? My understanding is that (aside from the high-bit-set condition
> you found) td->argument.value is semantically an addend; I certainly
> don't see any way it could already contain the desired symbol value
> (offset).
Yes, it's an addend, to the TLS segment's address, which is added later
on:
td->argument.value = value + sym_map->l_tls_offset;
in this code block. Note that sym->st_value is 0 in the local case
anyway, which is why current code works for this one.
However thanks for asking this question -- this is a bug fix that I made
long ago and you made me refresh some information. That in turn made me
realise there are three rather than two cases (local, global lazy and
global immediate) to be considered here and my fix only handles the two
formers, regressing the latter. We also need three test cases to cover
these variants. I'll send an update shortly.
Maciej
===================================================================
@@ -65,6 +65,7 @@ bind-now = @bindnow@
have-hash-style = @libc_cv_hashstyle@
use-default-link = @use_default_link@
output-format = @libc_cv_output_format@
+have-arm-tls-desc = @have_arm_tls_desc@
static-libgcc = @libc_cv_gcc_static_libgcc@
===================================================================
@@ -581,6 +581,7 @@ shared
static
ldd_rewrite_script
use_ldconfig
+have_arm_tls_desc
libc_cv_forced_unwind
libc_cv_rootsbindir
libc_cv_localstatedir
@@ -7225,6 +7226,7 @@ libc_cv_sysconfdir=$sysconfdir
libc_cv_localstatedir=$localstatedir
libc_cv_gcc_unwind_find_fde=no
libc_cv_idn=no
+have_arm_tls_desc=no
# Iterate over all the sysdep directories we will use, running their
# configure fragments.
@@ -7295,6 +7297,8 @@ fi
+
+
if test x$use_ldconfig = xyes; then
$as_echo "#define USE_LDCONFIG 1" >>confdefs.h
===================================================================
@@ -2065,6 +2065,7 @@ libc_cv_sysconfdir=$sysconfdir
libc_cv_localstatedir=$localstatedir
libc_cv_gcc_unwind_find_fde=no
libc_cv_idn=no
+have_arm_tls_desc=no
# Iterate over all the sysdep directories we will use, running their
# configure fragments.
@@ -2127,6 +2128,8 @@ AC_SUBST(libc_cv_localstatedir)
AC_SUBST(libc_cv_rootsbindir)
AC_SUBST(libc_cv_forced_unwind)
+AC_SUBST(have_arm_tls_desc)
+
if test x$use_ldconfig = xyes; then
AC_DEFINE(USE_LDCONFIG)
fi
===================================================================
@@ -11,6 +11,16 @@ $(objpfx)libgcc-stubs.a: $(objpfx)aeabi_
$(build-extra-lib)
lib-noranlib: $(objpfx)libgcc-stubs.a
+
+ifeq ($(build-shared),yes)
+ifeq ($(have-arm-tls-desc),yes)
+tests += tst-armtlsdesc
+modules-names += tst-armtlsdescmod
+CFLAGS-tst-armtlsdescmod.c += -mtls-dialect=gnu2
+tst-armtlsdesc-ENV = LD_BIND_NOW=1
+$(objpfx)tst-armtlsdesc: $(objpfx)tst-armtlsdescmod.so
+endif
+endif
endif
ifeq ($(subdir),csu)
===================================================================
@@ -203,3 +203,33 @@ else
config_vars="$config_vars
default-abi = soft"
fi
+
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking whether the build tools support the GNU descriptor TLS scheme" >&5
+$as_echo_n "checking whether the build tools support the GNU descriptor TLS scheme... " >&6; }
+if ${libc_cv_arm_tls_desc+:} false; then :
+ $as_echo_n "(cached) " >&6
+else
+ old_CFLAGS="$CFLAGS"
+ CFLAGS="$CFLAGS -mtls-dialect=gnu2"
+ cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h. */
+asm (".word\tfoo(tlsdesc)");
+int
+main ()
+{
+
+ ;
+ return 0;
+}
+_ACEOF
+if ac_fn_c_try_compile "$LINENO"; then :
+ libc_cv_arm_tls_desc=yes
+else
+ libc_cv_arm_tls_desc=no
+fi
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+ CFLAGS="$old_CFLAGS"
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_arm_tls_desc" >&5
+$as_echo "$libc_cv_arm_tls_desc" >&6; }
+have_arm_tls_desc=$libc_cv_arm_tls_desc
===================================================================
@@ -44,3 +44,12 @@ if test $libc_cv_arm_pcs_vfp = yes; then
else
LIBC_CONFIG_VAR([default-abi], [soft])
fi
+
+AC_CACHE_CHECK([whether the build tools support the GNU descriptor TLS scheme],
+ [libc_cv_arm_tls_desc],
+ [old_CFLAGS="$CFLAGS"
+ CFLAGS="$CFLAGS -mtls-dialect=gnu2"
+ AC_COMPILE_IFELSE([AC_LANG_PROGRAM([asm (".word\tfoo(tlsdesc)");], [])],
+ [libc_cv_arm_tls_desc=yes], [libc_cv_arm_tls_desc=no])
+ CFLAGS="$old_CFLAGS"])
+have_arm_tls_desc=$libc_cv_arm_tls_desc
===================================================================
@@ -452,7 +452,10 @@ elf_machine_rel (struct link_map *map, c
else
# endif
{
- value = sym->st_value + td->argument.value;
+ if (td->argument.value & 0x80000000)
+ value = sym->st_value;
+ else
+ value = td->argument.value;
# ifndef RTLD_BOOTSTRAP
# ifndef SHARED
===================================================================
@@ -0,0 +1,28 @@
+/* ARM immediate binding GNU TLS descriptor relocation test.
+ Copyright (C) 2013-2014 Free Software Foundation, Inc.
+ This file is part of the GNU C Library.
+
+ The GNU C Library is free software; you can redistribute it and/or
+ modify it under the terms of the GNU Lesser General Public
+ License as published by the Free Software Foundation; either
+ version 2.1 of the License, or (at your option) any later version.
+
+ The GNU C Library 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
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public
+ License along with the GNU C Library; if not, see
+ <http://www.gnu.org/licenses/>. */
+
+int getfoo (void);
+
+int
+do_test (void)
+{
+ return getfoo ();
+}
+
+#define TEST_FUNCTION do_test ()
+#include "../test-skeleton.c"
===================================================================
@@ -0,0 +1,25 @@
+/* DSO used for ARM immediate binding GNU TLS descriptor relocation test.
+ Copyright (C) 2013-2014 Free Software Foundation, Inc.
+ This file is part of the GNU C Library.
+
+ The GNU C Library is free software; you can redistribute it and/or
+ modify it under the terms of the GNU Lesser General Public
+ License as published by the Free Software Foundation; either
+ version 2.1 of the License, or (at your option) any later version.
+
+ The GNU C Library 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
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public
+ License along with the GNU C Library; if not, see
+ <http://www.gnu.org/licenses/>. */
+
+int __thread foo;
+
+int
+getfoo (void)
+{
+ return foo;
+}