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.

1 files changed, 24 insertions, 2 deletions

diff --git a/ld/configure b/ld/configure
index 17604bb..38f9739 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