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Re: RFC: x86: Enable -z separate-code by default
On Thu, Feb 22, 2018 at 6:25 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
> On Thu, Feb 22, 2018 at 5:22 AM, Michael Matz <matz@suse.de> wrote:
>> Hi,
>>
>> On Thu, 22 Feb 2018, H.J. Lu wrote:
>>
>>> >> Meh :-( Have you done any performance measurements on, say, SPECcpu?
>>> >
>>> > We will.
>>>
>>> We compared SPEC CPU 2017 performance before and after this change on
>>> Skylake server. There are no any significant performance changes.
>>> Everything is mostly below +/-1%.
>>
>> Thanks, seems fine.
>>
>>> >>> Should I add an ld configure option, --enable-separate-code, instead?
>>> >>
>>> >> Yes, definitely. For old distros at least I definitely want to retain old
>>> >> behaviour by default and a configure switch would make that easier.
>>> >
>>> > Will do.
>>> >
>>>
>>> Here is the patch to add --enable-separate-code to ld configure and
>>> enable it by default for Linux/x86. But the default maximum page size
>>> is changed to 4KB for x86-64.
>>>
>>> Any comments?
>>
>> Should the max page size setting (without override on cmdline) depend on
>> separate-code, or not? I'm split minds here, I'm worried that the 2mb
>
> I will give it a try.
>
Here is the patch which sets maximum page size to 2MB page size when
-z separate-code is disabled by default.
--
H.J.
From 5c7e47ff34a11b412a30c1f644f8a4d46074eb50 Mon Sep 17 00:00:00 2001
From: "H.J. Lu" <hjl.tools@gmail.com>
Date: Wed, 14 Feb 2018 04:09:05 -0800
Subject: [PATCH] ld: Add --enable-separate-code
This patch adds --enable-separate-code to ld configure to turn on
-z separate-code by default and enables it by default for Linux/x86.
This avoids mixing code pages with data to improve cache performance
as well as security.
To reduce x86-64 executable and shared object sizes, the maximum page
size is reduced from 2MB to 4KB when -z separate-code is turned on by
default. Note: -z max-page-size= can be used to set the maximum page
size.
We compared SPEC CPU 2017 performance before and after this change on
Skylake server. There are no any significant performance changes.
Everything is mostly below +/-1%.
bfd/
* config.in: Regenerated.
* configure: Likewise.
* configure.ac: Add --enable-separate-code.
(DEFAULT_LD_Z_SEPARATE_CODE): New AC_DEFINE_UNQUOTED. Default
to 1 for Linux/x86 targets,
* elf64-x86-64.c (ELF_MAXPAGESIZE): Set to 0x1000 if
DEFAULT_LD_Z_SEPARATE_CODE is 1.
ld/
* NEWS: Mention --enable-separate-code.
* configure.ac: Add --enable-separate-code.
(DEFAULT_LD_Z_SEPARATE_CODE): New AC_DEFINE_UNQUOTED.
* configure.tgt: Default ac_default_ld_z_separate_code to 1 for
Linux/x86 targets.
* config.in: Regenerated.
* configure: Likewise.
* emultempl/elf32.em (gld${EMULATION_NAME}_before_parse): Set
link_info.separate_code DEFAULT_LD_Z_SEPARATE_CODE.
---
bfd/config.in | 4 ++++
bfd/configure | 33 +++++++++++++++++++++++++++++++--
bfd/configure.ac | 24 ++++++++++++++++++++++++
bfd/elf64-x86-64.c | 12 ++++++++++--
ld/NEWS | 5 +++++
ld/config.in | 4 ++++
ld/configure | 26 ++++++++++++++++++++++++--
ld/configure.ac | 17 +++++++++++++++++
ld/configure.tgt | 9 +++++++++
ld/emultempl/elf32.em | 1 +
10 files changed, 129 insertions(+), 6 deletions(-)
diff --git a/bfd/config.in b/bfd/config.in
index 75a5ff015e..186741d612 100644
--- a/bfd/config.in
+++ b/bfd/config.in
@@ -10,6 +10,10 @@
/* Name of host specific core header file to include in elf.c. */
#undef CORE_HEADER
+/* Define to 1 if you want to enable -z separate-code in ELF linker by
+ default. */
+#undef DEFAULT_LD_Z_SEPARATE_CODE
+
/* Define to 1 if translation of program messages to the user's native
language is requested. */
#undef ENABLE_NLS
diff --git a/bfd/configure b/bfd/configure
index 6c2b24ebe3..d1fe335530 100755
--- a/bfd/configure
+++ b/bfd/configure
@@ -793,6 +793,7 @@ enable_targets
enable_64_bit_archive
with_mmap
enable_secureplt
+enable_separate_code
enable_leading_mingw64_underscores
with_separate_debug_dir
with_pkgversion
@@ -1446,6 +1447,7 @@ Optional Features:
--enable-targets alternative target configurations
--enable-64-bit-archive force 64-bit archives
--enable-secureplt Default to creating read-only plt entries
+ --enable-separate-code enable -z separate-code in ELF linker by default
--enable-leading-mingw64-underscores
Enable leading underscores on 64 bit mingw targets
--enable-werror treat compile warnings as errors
@@ -11428,7 +11430,7 @@ else
lt_dlunknown=0; lt_dlno_uscore=1; lt_dlneed_uscore=2
lt_status=$lt_dlunknown
cat > conftest.$ac_ext <<_LT_EOF
-#line 11431 "configure"
+#line 11433 "configure"
#include "confdefs.h"
#if HAVE_DLFCN_H
@@ -11534,7 +11536,7 @@ else
lt_dlunknown=0; lt_dlno_uscore=1; lt_dlneed_uscore=2
lt_status=$lt_dlunknown
cat > conftest.$ac_ext <<_LT_EOF
-#line 11537 "configure"
+#line 11539 "configure"
#include "confdefs.h"
#if HAVE_DLFCN_H
@@ -12171,6 +12173,33 @@ $as_echo "#define USE_SECUREPLT 1" >>confdefs.h
fi
+# Decide if -z separate-code should be enabled in ELF linker by default.
+ac_default_ld_z_separate_code=unset
+# Check whether --enable-separate-code was given.
+if test "${enable_separate_code+set}" = set; then :
+ enableval=$enable_separate_code; case "${enableval}" in
+ yes) ac_default_ld_z_separate_code=1 ;;
+ no) ac_default_ld_z_separate_code=0 ;;
+esac
+fi
+
+# Enable -z separate-code by default for Linux/x86.
+case "${target}" in
+i3-786-*-linux-* | x86_64-*-linux-*)
+ if test ${ac_default_ld_z_separate_code} = unset; then
+ ac_default_ld_z_separate_code=1
+ fi
+ ;;
+esac
+if test "${ac_default_ld_z_separate_code}" = unset; then
+ ac_default_ld_z_separate_code=0
+fi
+
+cat >>confdefs.h <<_ACEOF
+#define DEFAULT_LD_Z_SEPARATE_CODE $ac_default_ld_z_separate_code
+_ACEOF
+
+
# Check whether --enable-leading-mingw64-underscores was given.
if test "${enable_leading_mingw64_underscores+set}" = set; then :
enableval=$enable_leading_mingw64_underscores;
diff --git a/bfd/configure.ac b/bfd/configure.ac
index 2342f3faea..20e2c022e8 100644
--- a/bfd/configure.ac
+++ b/bfd/configure.ac
@@ -97,6 +97,30 @@ if test $use_secureplt = true; then
[Define if we should default to creating read-only plt entries])
fi
+# Decide if -z separate-code should be enabled in ELF linker by default.
+ac_default_ld_z_separate_code=unset
+AC_ARG_ENABLE(separate-code,
+ AS_HELP_STRING([--enable-separate-code],
+ [enable -z separate-code in ELF linker by default]),
+[case "${enableval}" in
+ yes) ac_default_ld_z_separate_code=1 ;;
+ no) ac_default_ld_z_separate_code=0 ;;
+esac])
+# Enable -z separate-code by default for Linux/x86.
+case "${target}" in
+i[3-7]86-*-linux-* | x86_64-*-linux-*)
+ if test ${ac_default_ld_z_separate_code} = unset; then
+ ac_default_ld_z_separate_code=1
+ fi
+ ;;
+esac
+if test "${ac_default_ld_z_separate_code}" = unset; then
+ ac_default_ld_z_separate_code=0
+fi
+AC_DEFINE_UNQUOTED(DEFAULT_LD_Z_SEPARATE_CODE,
+ $ac_default_ld_z_separate_code,
+ [Define to 1 if you want to enable -z separate-code in ELF linker by default.])
+
AC_ARG_ENABLE(leading-mingw64-underscores,
AS_HELP_STRING([--enable-leading-mingw64-underscores],
[Enable leading underscores on 64 bit mingw targets]),
diff --git a/bfd/elf64-x86-64.c b/bfd/elf64-x86-64.c
index d66d9ba5fc..7e0eb1a32b 100644
--- a/bfd/elf64-x86-64.c
+++ b/bfd/elf64-x86-64.c
@@ -4936,7 +4936,11 @@ elf_x86_64_special_sections[]=
#define ELF_ARCH bfd_arch_i386
#define ELF_TARGET_ID X86_64_ELF_DATA
#define ELF_MACHINE_CODE EM_X86_64
-#define ELF_MAXPAGESIZE 0x200000
+#if DEFAULT_LD_Z_SEPARATE_CODE
+# define ELF_MAXPAGESIZE 0x1000
+#else
+# define ELF_MAXPAGESIZE 0x200000
+#endif
#define ELF_MINPAGESIZE 0x1000
#define ELF_COMMONPAGESIZE 0x1000
@@ -5329,7 +5333,11 @@ elf64_l1om_elf_object_p (bfd *abfd)
#undef ELF_MAXPAGESIZE
#undef ELF_MINPAGESIZE
#undef ELF_COMMONPAGESIZE
-#define ELF_MAXPAGESIZE 0x200000
+#if DEFAULT_LD_Z_SEPARATE_CODE
+# define ELF_MAXPAGESIZE 0x1000
+#else
+# define ELF_MAXPAGESIZE 0x200000
+#endif
#define ELF_MINPAGESIZE 0x1000
#define ELF_COMMONPAGESIZE 0x1000
#undef elf_backend_plt_alignment
diff --git a/ld/NEWS b/ld/NEWS
index eafcaf33cb..75f8100f87 100644
--- a/ld/NEWS
+++ b/ld/NEWS
@@ -1,5 +1,10 @@
-*- text -*-
+* Add a configure option --enable-separate-code to decide whether
+ -z separate-code should be enabled in ELF linker by default. Default
+ to yes for Linux/x86 targets. Note that -z separate-code can increase
+ disk and memory size.
+
Changes in 2.30:
* Add -z separate-code to generate separate code PT_LOAD segment.
diff --git a/ld/config.in b/ld/config.in
index a846743da6..b227a53984 100644
--- a/ld/config.in
+++ b/ld/config.in
@@ -19,6 +19,10 @@
/* Define to 1 if you want to enable -z relro in ELF linker by default. */
#undef DEFAULT_LD_Z_RELRO
+/* Define to 1 if you want to enable -z separate-code in ELF linker by
+ default. */
+#undef DEFAULT_LD_Z_SEPARATE_CODE
+
/* Define to 1 if you want to set DT_RUNPATH instead of DT_RPATH by default.
*/
#undef DEFAULT_NEW_DTAGS
diff --git a/ld/configure b/ld/configure
index 0cc6e8a50f..241ac8f90e 100755
--- a/ld/configure
+++ b/ld/configure
@@ -790,6 +790,7 @@ enable_got
enable_compressed_debug_sections
enable_new_dtags
enable_relro
+enable_separate_code
enable_default_hash_style
enable_werror
enable_build_warnings
@@ -1451,6 +1452,7 @@ Optional Features:
compress debug sections by default]
--enable-new-dtags set DT_RUNPATH instead of DT_RPATH by default]
--enable-relro enable -z relro in ELF linker by default
+ --enable-separate-code enable -z separate-code in ELF linker by default
--enable-default-hash-style={sysv,gnu,both}
use this default hash style
--enable-werror treat compile warnings as errors
@@ -11725,7 +11727,7 @@ else
lt_dlunknown=0; lt_dlno_uscore=1; lt_dlneed_uscore=2
lt_status=$lt_dlunknown
cat > conftest.$ac_ext <<_LT_EOF
-#line 11728 "configure"
+#line 11730 "configure"
#include "confdefs.h"
#if HAVE_DLFCN_H
@@ -11831,7 +11833,7 @@ else
lt_dlunknown=0; lt_dlno_uscore=1; lt_dlneed_uscore=2
lt_status=$lt_dlunknown
cat > conftest.$ac_ext <<_LT_EOF
-#line 11834 "configure"
+#line 11836 "configure"
#include "confdefs.h"
#if HAVE_DLFCN_H
@@ -15567,6 +15569,17 @@ if test "${enable_relro+set}" = set; then :
esac
fi
+# Decide if -z separate-code should be enabled in ELF linker by default.
+ac_default_ld_z_separate_code=unset
+# Check whether --enable-separate-code was given.
+if test "${enable_separate_code+set}" = set; then :
+ enableval=$enable_separate_code; case "${enableval}" in
+ yes) ac_default_ld_z_separate_code=1 ;;
+ no) ac_default_ld_z_separate_code=0 ;;
+esac
+fi
+
+
# Decide which "--hash-style" to use by default
# Provide a configure time option to override our default.
# Check whether --enable-default-hash-style was given.
@@ -17258,6 +17271,15 @@ cat >>confdefs.h <<_ACEOF
_ACEOF
+if test "${ac_default_ld_z_separate_code}" = unset; then
+ ac_default_ld_z_separate_code=0
+fi
+
+cat >>confdefs.h <<_ACEOF
+#define DEFAULT_LD_Z_SEPARATE_CODE $ac_default_ld_z_separate_code
+_ACEOF
+
+
cat >>confdefs.h <<_ACEOF
#define DEFAULT_EMIT_SYSV_HASH $ac_default_emit_sysv_hash
diff --git a/ld/configure.ac b/ld/configure.ac
index bada1b50b0..5554873485 100644
--- a/ld/configure.ac
+++ b/ld/configure.ac
@@ -177,6 +177,16 @@ AC_ARG_ENABLE(relro,
no) ac_default_ld_z_relro=0 ;;
esac])dnl
+# Decide if -z separate-code should be enabled in ELF linker by default.
+ac_default_ld_z_separate_code=unset
+AC_ARG_ENABLE(separate-code,
+ AS_HELP_STRING([--enable-separate-code],
+ [enable -z separate-code in ELF linker by default]),
+[case "${enableval}" in
+ yes) ac_default_ld_z_separate_code=1 ;;
+ no) ac_default_ld_z_separate_code=0 ;;
+esac])
+
# Decide which "--hash-style" to use by default
# Provide a configure time option to override our default.
AC_ARG_ENABLE([default-hash-style],
@@ -434,6 +444,13 @@ AC_DEFINE_UNQUOTED(DEFAULT_LD_Z_RELRO,
$ac_default_ld_z_relro,
[Define to 1 if you want to enable -z relro in ELF linker by default.])
+if test "${ac_default_ld_z_separate_code}" = unset; then
+ ac_default_ld_z_separate_code=0
+fi
+AC_DEFINE_UNQUOTED(DEFAULT_LD_Z_SEPARATE_CODE,
+ $ac_default_ld_z_separate_code,
+ [Define to 1 if you want to enable -z separate-code in ELF linker by default.])
+
AC_DEFINE_UNQUOTED([DEFAULT_EMIT_SYSV_HASH],
[$ac_default_emit_sysv_hash],
[Define to 1 if you want to emit sysv hash in the ELF linker by default.])
diff --git a/ld/configure.tgt b/ld/configure.tgt
index 6183a85b3d..7897448e64 100644
--- a/ld/configure.tgt
+++ b/ld/configure.tgt
@@ -968,3 +968,12 @@ frv-*-* | hppa*-*-* | ia64-*-* | mips*-*-*)
fi
;;
esac
+
+# Enable -z separate-code by default for Linux/x86.
+case "${target}" in
+i[3-7]86-*-linux-* | x86_64-*-linux-*)
+ if test ${ac_default_ld_z_separate_code} = unset; then
+ ac_default_ld_z_separate_code=1
+ fi
+ ;;
+esac
diff --git a/ld/emultempl/elf32.em b/ld/emultempl/elf32.em
index eb90743cee..e21b3e3300 100644
--- a/ld/emultempl/elf32.em
+++ b/ld/emultempl/elf32.em
@@ -106,6 +106,7 @@ gld${EMULATION_NAME}_before_parse (void)
`if test -n "$CALL_NOP_BYTE" ; then echo link_info.call_nop_byte = $CALL_NOP_BYTE; fi`;
link_info.check_relocs_after_open_input = TRUE;
link_info.relro = DEFAULT_LD_Z_RELRO;
+ link_info.separate_code = DEFAULT_LD_Z_SEPARATE_CODE;
}
EOF
--
2.14.3