Hi Joseph/Jakub,
Attached is Version 2 patch that adds machine descriptions for stack
protection in Aarch64. I have removed the incorrect test case changes
from the previous patch.
To make GCC compatible with glibc, I have added a test for aarch64 in
"GCC/configure".
This tests for the glibc version >= 2.19, generate TLS based stack
guard access, otherwise will fall back to global variable
__stack_chk_guard based access.
Also I will be submitting a glibc patch to export __stack_chk_guard
and initialize it with proper value, to make sure that it coexists
with TLS based stack guard access for aarch64.
I have posted code snippet here.
http://gcc.gnu.org/ml/gcc-patches/2013-11/msg02968.html
ChangeLog:
2013-11-26 Venkataramanan Kumar <venkataramanan.ku...@linaro.org>
* configure.ac (gcc_cv_libc_provides_tls_ssp): Add test to
check TLS support in target C library for Aarch64.
* configure: Regenerate.
* config.in: Regenerate.
* config/aarch64/aarch64.md (stack_protect_set, stack_protect_test)
(stack_protect_set_<mode>, stack_protect_test_<mode>): Add
initial machine description for Stack Smashing Protector.
* config/aarch64/aarch64-linux.h (TARGET_THREAD_SSP_OFFSET): Define.
2013-11-26 Venkataramanan Kumar <venkataramanan.ku...@linaro.org>
* g++.dg/fstack-protector-strong.C: Add aarch64 target.
* gcc.dg/fstack-protector-strong.c: Likewise.
Let me know your feed back and please advice on improving it further.
regards,
Venkat.
On 23 November 2013 09:32, Venkataramanan Kumar
<venkataramanan.ku...@linaro.org> wrote:
> Hi Joseph,
>
> Thank you for the detail explanation.
>
>> You need to ensure that, when new glibc is built, whatever compiler it's
>> built with, it continues to export the __stack_chk_guard symbol at version
>> GLIBC_2.17. Furthermore, if any released GCC version would generate
>> references to __stack_chk_guard when compiling code for AArch64 with stack
>> protection, you need to ensure __stack_chk_guard is a normal symbol not a
>> compat symbol so that people can continue to link against new glibc when
>> using old GCC. If it's only a limited range of development versions of
>> GCC that could have generated code using __stack_chk_guard because
>> released versions didn't support stack protection on AArch64 at all, a
>> compat symbol would probably be OK (but you should still ensure that the
>> variable gets initialized with the correct value for any applications
>> built with those development versions of GCC).
>
> As you said when THREAD_SET_STACK_GUARD is set glibc does not export
> __stack_chk_guard. So I am planning to change the export logic by
> adding a new macro EXPORT_GLOBAL_STACK_GUARD
> and set it for Aarch64 port in glibc.
>
> ----snip----
> --- a/csu/libc-start.c
> +++ b/csu/libc-start.c
> -# ifndef THREAD_SET_STACK_GUARD
> +
> +#if !defined(THREAD_SET_STACK_GUARD) || defined(EXPORT_GLOBAL_STACK_GUARD)
> /* Only exported for architectures that don't store the stack guard canary
> in thread local area. */
> uintptr_t __stack_chk_guard attribute_relro;
> -# endif
> +#endif
> +
> ----snip----
>
> I will find a better way to version that symbol as well. I will sent a
> RFC patch to glibc mailing list.
>
> On the GCC side, trunk GCC configure script checks and sets
> TARGET_LIBC_PROVIDES_SSP support when glibc is >=2.4
>
> -----snip----
> # Test for stack protector support in target C library.
> { $as_echo "$as_me:${as_lineno-$LINENO}: checking __stack_chk_fail in
> target C library" >&5
> $as_echo_n "checking __stack_chk_fail in target C library... " >&6; }
> if test "${gcc_cv_libc_provides_ssp+set}" = set; then :
> $as_echo_n "(cached) " >&6
> else
> gcc_cv_libc_provides_ssp=no
> case "$target" in
> *-*-linux* | *-*-kfreebsd*-gnu | *-*-knetbsd*-gnu)
> # glibc 2.4 and later provides __stack_chk_fail and
> # either __stack_chk_guard, or TLS access to stack guard canary.
>
> if test $glibc_version_major -gt 2 \
> || ( test $glibc_version_major -eq 2 && test $glibc_version_minor
> -ge 4 ); then :
> gcc_cv_libc_provides_ssp=yes
>
>
> if test x$gcc_cv_libc_provides_ssp = xyes; then
>
> $as_echo "#define TARGET_LIBC_PROVIDES_SSP 1" >>confdefs.h
> fi
> ----snip-----
>
> To make GCC for AArch64 generate TLS based stack access for glibc >=
> 2.19 I need to introduce a new macro
> TARGET_LIBC_PROVIDES_TLS_SSP and check and set it for glibc >= 2.19 in
> GCC configure .
>
> Any better approach to this since it is specific to Aarch64?
>
> regards,
> Venkat.
>
> On 20 November 2013 22:38, Joseph S. Myers <jos...@codesourcery.com> wrote:
>> On Wed, 20 Nov 2013, Venkataramanan Kumar wrote:
>>
>>> > I would like to see a clear description of what happens with all eight
>>> > combinations of (glibc version does or doesn't support this, GCC building
>>> > glibc does or doesn't support this, GCC building user program does or
>>> > doesn't support this). Which of the (GCC building glibc, glibc)
>>> > combinations will successfully build glibc? Will all such glibcs be
>>> > binary-compatible? Will both old and new GCC work for building user
>>> > programs with both old and new glibc?
>>>
>>> Can you please clarify why we need to consider "the gcc compiler that
>>> builds the glibc" in the combinations you want me to describe. I am
>>> not able to understand that.
>>
>> Let's imagine this support goes in GCC 4.9 and the glibc support goes in
>> glibc 2.19, whereas GCC 4.8 and glibc 2.18 are versions without this
>> support.
>>
>> * Building glibc 2.18 with GCC 4.8 already works (I presume).
>>
>> * Suppose you use GCC 4.9 to build glibc 2.18. Does this work? If it
>> works, it must produce a glibc binary that's ABI compatible with one built
>> with GCC 4.8, meaning same symbols exported at same symbol versions.
>>
>> * Suppose you build glibc 2.19 with GCC 4.8. Does this work? If it does,
>> then it must be ABI compatible with 2.18 (meaning the symbols exported at
>> GLIBC_2.18 or earlier versions must be exactly the same as exported at
>> those versions in 2.18).
>>
>> * Suppose you build glibc 2.19 with GCC 4.9. This needs to work and must
>> again produce a binary compatible with the previous ones.
>>
>> Note: there is no current glibc support for architectures that gained
>> TLS-based stack guards after 2.4 (meaning they need both a TLS-based
>> scheme and backwards compatibility for binaries using __stack_chk_guard),
>> and your glibc patch doesn't seem to add any. It looks to me like your
>> glibc patch would have removed the __stack_chk_guard symbol and so failed
>> ABI tests (this symbol being defined only if THREAD_SET_STACK_GUARD isn't
>> defined) - you didn't make clear if your patch was tested with the glibc
>> testsuite including passing the ABI tests. The normal presumption is that
>> it's not acceptable to remove exported symbols from glibc as some
>> application might be using them.
>>
>> You need to ensure that, when new glibc is built, whatever compiler it's
>> built with, it continues to export the __stack_chk_guard symbol at version
>> GLIBC_2.17. Furthermore, if any released GCC version would generate
>> references to __stack_chk_guard when compiling code for AArch64 with stack
>> protection, you need to ensure __stack_chk_guard is a normal symbol not a
>> compat symbol so that people can continue to link against new glibc when
>> using old GCC. If it's only a limited range of development versions of
>> GCC that could have generated code using __stack_chk_guard because
>> released versions didn't support stack protection on AArch64 at all, a
>> compat symbol would probably be OK (but you should still ensure that the
>> variable gets initialized with the correct value for any applications
>> built with those development versions of GCC).
>>
>> --
>> Joseph S. Myers
>> jos...@codesourcery.com
Index: gcc/config/aarch64/aarch64-linux.h
===================================================================
--- gcc/config/aarch64/aarch64-linux.h (revision 205378)
+++ gcc/config/aarch64/aarch64-linux.h (working copy)
@@ -43,4 +43,9 @@
} \
while (0)
+#ifdef TARGET_LIBC_PROVIDES_TLS_SSP
+/* Aarch64 glibc provides __stack_chk_guard in [tp - 0x8]. */
+#define TARGET_THREAD_SSP_OFFSET (-1 * GET_MODE_SIZE (ptr_mode))
+#endif
+
#endif /* GCC_AARCH64_LINUX_H */
Index: gcc/config/aarch64/aarch64.md
===================================================================
--- gcc/config/aarch64/aarch64.md (revision 205378)
+++ gcc/config/aarch64/aarch64.md (working copy)
@@ -99,6 +99,10 @@
UNSPEC_TLSDESC
UNSPEC_USHL_2S
UNSPEC_VSTRUCTDUMMY
+ UNSPEC_SP_SET
+ UNSPEC_SP_TEST
+ UNSPEC_SP_TLS_SET
+ UNSPEC_SP_TLS_TEST
])
(define_c_enum "unspecv" [
@@ -3625,6 +3629,80 @@
DONE;
})
+
+;; Named patterns for stack smashing protection.
+(define_expand "stack_protect_set"
+ [(match_operand 0 "memory_operand")
+ (match_operand 1 "memory_operand")]
+ ""
+{
+ enum machine_mode mode = GET_MODE (operands[0]);
+
+#ifdef TARGET_THREAD_SSP_OFFSET
+ rtx tlsreg = gen_reg_rtx (Pmode);
+ emit_insn (gen_aarch64_load_tp_hard (tlsreg));
+ rtx addr = gen_rtx_PLUS (Pmode, tlsreg, GEN_INT (TARGET_THREAD_SSP_OFFSET));
+ operands[1] = gen_rtx_MEM (Pmode, addr);
+#endif
+
+ emit_insn ((mode == DImode
+ ? gen_stack_protect_set_di
+ : gen_stack_protect_set_si) (operands[0], operands[1]));
+ DONE;
+})
+
+(define_insn "stack_protect_set_<mode>"
+ [(set (match_operand:PTR 0 "memory_operand" "=m")
+ (unspec:PTR [(match_operand:PTR 1 "memory_operand" "m")]
+ UNSPEC_SP_SET))
+ (set (match_scratch:PTR 2 "=&r") (const_int 0))]
+ ""
+ "ldr\\t%x2, %1\;str\\t%x2, %0\;mov\t%x2,0"
+ [(set_attr "length" "12")])
+
+(define_expand "stack_protect_test"
+ [(match_operand 0 "memory_operand")
+ (match_operand 1 "memory_operand")
+ (match_operand 2)]
+ ""
+{
+
+#ifdef TARGET_THREAD_SSP_OFFSET
+ rtx tlsreg = gen_reg_rtx (Pmode);
+ emit_insn (gen_aarch64_load_tp_hard (tlsreg));
+ rtx addr = gen_rtx_PLUS (Pmode, tlsreg, GEN_INT (TARGET_THREAD_SSP_OFFSET));
+ operands[1] = gen_rtx_MEM (Pmode, addr);
+#endif
+
+ rtx result = gen_reg_rtx (Pmode);
+
+ enum machine_mode mode = GET_MODE (operands[0]);
+
+ emit_insn ((mode == DImode
+ ? gen_stack_protect_test_di
+ : gen_stack_protect_test_si) (result,
+ operands[0],
+ operands[1]));
+
+ if (mode == DImode)
+ emit_jump_insn (gen_cbranchdi4 (gen_rtx_EQ (VOIDmode, result, const0_rtx),
+ result, const0_rtx, operands[2]));
+ else
+ emit_jump_insn (gen_cbranchsi4 (gen_rtx_EQ (VOIDmode, result, const0_rtx),
+ result, const0_rtx, operands[2]));
+ DONE;
+})
+
+(define_insn "stack_protect_test_<mode>"
+ [(set (match_operand:PTR 0 "register_operand")
+ (unspec:PTR [(match_operand:PTR 1 "memory_operand" "m")
+ (match_operand:PTR 2 "memory_operand" "m")]
+ UNSPEC_SP_TEST))
+ (clobber (match_scratch:PTR 3 "=&r"))]
+ ""
+ "ldr\t%x3, %x1\;ldr\t%x0, %x2\;eor\t%x0, %x3, %x0"
+ [(set_attr "length" "12")])
+
;; AdvSIMD Stuff
(include "aarch64-simd.md")
Index: gcc/configure
===================================================================
--- gcc/configure (revision 205378)
+++ gcc/configure (working copy)
@@ -27127,6 +27127,35 @@
fi
+# Test for tls based stack protector support in target C library.
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking TLS stack guard support in
target C library" >&5
+$as_echo_n "checking TLS stack guard support in target C library... " >&6; }
+if test "${gcc_cv_libc_provides_tls_ssp+set}" = set; then :
+ $as_echo_n "(cached) " >&6
+else
+ gcc_cv_libc_provides_tls_ssp=no
+ case "$target" in
+ aarch64-*-linux* | aarch64-*-kfreebsd*-gnu | aarch64-*-knetbsd*-gnu)
+ # glibc 2.19 and later provides TLS access to stack guard canary
+ # currently set for Aarch64.
+
+if test $glibc_version_major -gt 2 \
+ || ( test $glibc_version_major -eq 2 && test $glibc_version_minor -ge 19 );
then :
+ gcc_cv_libc_provides_tls_ssp=yes
+fi
+ ;;
+ *) gcc_cv_libc_provides_tls_ssp=no ;;
+ esac
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result:
$gcc_cv_libc_provides_tls_ssp" >&5
+$as_echo "$gcc_cv_libc_provides_tls_ssp" >&6; }
+
+if test x$gcc_cv_libc_provides_tls_ssp = xyes; then
+
+$as_echo "#define TARGET_LIBC_PROVIDES_TLS_SSP 1" >>confdefs.h
+
+fi
+
# Test for <sys/sdt.h> on the target.
{ $as_echo "$as_me:${as_lineno-$LINENO}: checking sys/sdt.h in the target C
library" >&5
Index: gcc/testsuite/gcc.dg/fstack-protector-strong.c
===================================================================
--- gcc/testsuite/gcc.dg/fstack-protector-strong.c (revision 205378)
+++ gcc/testsuite/gcc.dg/fstack-protector-strong.c (working copy)
@@ -1,6 +1,6 @@
/* Test that stack protection is done on chosen functions. */
-/* { dg-do compile { target i?86-*-* x86_64-*-* rs6000-*-* s390x-*-* } } */
+/* { dg-do compile { target i?86-*-* x86_64-*-* rs6000-*-* s390x-*-*
aarch64-*-* } } */
/* { dg-options "-O2 -fstack-protector-strong" } */
#include<string.h>
Index: gcc/testsuite/g++.dg/fstack-protector-strong.C
===================================================================
--- gcc/testsuite/g++.dg/fstack-protector-strong.C (revision 205378)
+++ gcc/testsuite/g++.dg/fstack-protector-strong.C (working copy)
@@ -1,6 +1,6 @@
/* Test that stack protection is done on chosen functions. */
-/* { dg-do compile { target i?86-*-* x86_64-*-* } } */
+/* { dg-do compile { target i?86-*-* x86_64-*-* aarch64*-*-* } } */
/* { dg-options "-O2 -fstack-protector-strong" } */
class A
Index: gcc/config.in
===================================================================
--- gcc/config.in (revision 205378)
+++ gcc/config.in (working copy)
@@ -1828,6 +1828,12 @@
#endif
+/* Define if your target C library provides TLS stack protector support. */
+#ifndef USED_FOR_TARGET
+#undef TARGET_LIBC_PROVIDES_TLS_SSP
+#endif
+
+
/* Define to 1 if you can safely include both <sys/time.h> and <time.h>. */
#ifndef USED_FOR_TARGET
#undef TIME_WITH_SYS_TIME
Index: gcc/configure.ac
===================================================================
--- gcc/configure.ac (revision 205378)
+++ gcc/configure.ac (working copy)
@@ -4896,6 +4896,24 @@
[Define if your target C library provides stack protector support])
fi
+# Test for tls based stack protector support in target C library.
+AC_CACHE_CHECK(TLS stack guard support in target C library,
+ gcc_cv_libc_provides_tls_ssp,
+ [gcc_cv_libc_provides_tls_ssp=no
+ case "$target" in
+ aarch64-*-linux* | aarch64-*-kfreebsd*-gnu | aarch64-*-knetbsd*-gnu)
+ # glibc 2.19 and later provides TLS access to stack guard canary
+ # currently set for Aarch64.
+ GCC_GLIBC_VERSION_GTE_IFELSE([2], [19],
[gcc_cv_libc_provides_tls_ssp=yes])
+ ;;
+ *) gcc_cv_libc_provides_tls_ssp=no ;;
+ esac])
+
+if test x$gcc_cv_libc_provides_tls_ssp = xyes; then
+ AC_DEFINE(TARGET_LIBC_PROVIDES_TLS_SSP, 1,
+ [Define if your target C library provides TLS stack protector
support.])
+fi
+
# Test for <sys/sdt.h> on the target.
GCC_TARGET_TEMPLATE([HAVE_SYS_SDT_H])
AC_MSG_CHECKING(sys/sdt.h in the target C library)
