Re: RFC: x86: Enable -z separate-code by default

[Michael Matz <matz at suse dot de>]

Hi,

On Mon, 19 Feb 2018, H.J. Lu wrote:

> This patch enables -z separate-code by default for x86.  To reduce
> x86-64 binary size, set ELF_MAXPAGESIZE to 4KB.

Meh :-(  Have you done any performance measurements on, say, SPECcpu?

> 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.


Ciao,
Michael.

> 
> 
> H.J.
> ---
> bfd/
> 	* elf64-x86-64.c (ELF_MAXPAGESIZE): Set to 0x1000.
> 
> ld/
> 
> 	* emulparams/elf32_x86_64.sh (DEFAULT_SEPARATE_CODE): New.
> 	* emulparams/elf_i386.sh (DEFAULT_SEPARATE_CODE): Likewise.
> 	* emulparams/elf_x86_64.sh (DEFAULT_SEPARATE_CODE): Likewise.
> 	* emultempl/elf32.em (gld${EMULATION_NAME}_before_parse): Set
> 	link_info.separate_code to TRUE if ${DEFAULT_SEPARATE_CODE} is
> 	yes.
> ---
>  bfd/elf64-x86-64.c            | 4 ++--
>  ld/emulparams/elf32_x86_64.sh | 1 +
>  ld/emulparams/elf_i386.sh     | 1 +
>  ld/emulparams/elf_x86_64.sh   | 1 +
>  ld/emultempl/elf32.em         | 1 +
>  5 files changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/bfd/elf64-x86-64.c b/bfd/elf64-x86-64.c
> index 00ed5d17a5..51c301bae6 100644
> --- a/bfd/elf64-x86-64.c
> +++ b/bfd/elf64-x86-64.c
> @@ -4934,7 +4934,7 @@ 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
> +#define ELF_MAXPAGESIZE			    0x1000
>  #define ELF_MINPAGESIZE			    0x1000
>  #define ELF_COMMONPAGESIZE		    0x1000
>  
> @@ -5327,7 +5327,7 @@ elf64_l1om_elf_object_p (bfd *abfd)
>  #undef	ELF_MAXPAGESIZE
>  #undef	ELF_MINPAGESIZE
>  #undef	ELF_COMMONPAGESIZE
> -#define ELF_MAXPAGESIZE			0x200000
> +#define ELF_MAXPAGESIZE			0x1000
>  #define ELF_MINPAGESIZE			0x1000
>  #define ELF_COMMONPAGESIZE		0x1000
>  #undef	elf_backend_plt_alignment
> diff --git a/ld/emulparams/elf32_x86_64.sh b/ld/emulparams/elf32_x86_64.sh
> index 9ce6533bd9..f8e004829d 100644
> --- a/ld/emulparams/elf32_x86_64.sh
> +++ b/ld/emulparams/elf32_x86_64.sh
> @@ -14,6 +14,7 @@ COMMONPAGESIZE="CONSTANT (COMMONPAGESIZE)"
>  ARCH="i386:x64-32"
>  MACHINE=
>  TEMPLATE_NAME=elf32
> +DEFAULT_SEPARATE_CODE=yes
>  GENERATE_SHLIB_SCRIPT=yes
>  GENERATE_PIE_SCRIPT=yes
>  NO_SMALL_DATA=yes
> diff --git a/ld/emulparams/elf_i386.sh b/ld/emulparams/elf_i386.sh
> index 2cef106e3d..6c451aac8a 100644
> --- a/ld/emulparams/elf_i386.sh
> +++ b/ld/emulparams/elf_i386.sh
> @@ -12,6 +12,7 @@ COMMONPAGESIZE="CONSTANT (COMMONPAGESIZE)"
>  ARCH=i386
>  MACHINE=
>  TEMPLATE_NAME=elf32
> +DEFAULT_SEPARATE_CODE=yes
>  GENERATE_SHLIB_SCRIPT=yes
>  GENERATE_PIE_SCRIPT=yes
>  NO_SMALL_DATA=yes
> diff --git a/ld/emulparams/elf_x86_64.sh b/ld/emulparams/elf_x86_64.sh
> index d8c6e54894..8e18d81bdf 100644
> --- a/ld/emulparams/elf_x86_64.sh
> +++ b/ld/emulparams/elf_x86_64.sh
> @@ -14,6 +14,7 @@ COMMONPAGESIZE="CONSTANT (COMMONPAGESIZE)"
>  ARCH="i386:x86-64"
>  MACHINE=
>  TEMPLATE_NAME=elf32
> +DEFAULT_SEPARATE_CODE=yes
>  GENERATE_SHLIB_SCRIPT=yes
>  GENERATE_PIE_SCRIPT=yes
>  NO_SMALL_DATA=yes
> diff --git a/ld/emultempl/elf32.em b/ld/emultempl/elf32.em
> index c0925fc9b9..1325b4742f 100644
> --- a/ld/emultempl/elf32.em
> +++ b/ld/emultempl/elf32.em
> @@ -104,6 +104,7 @@ gld${EMULATION_NAME}_before_parse (void)
>    config.has_shared = `if test -n "$GENERATE_SHLIB_SCRIPT" ; then echo TRUE ; else echo FALSE ; fi`;
>    config.separate_code = `if test "x${SEPARATE_CODE}" = xyes ; then echo TRUE ; else echo FALSE ; fi`;
>    `if test -n "$CALL_NOP_BYTE" ; then echo link_info.call_nop_byte = $CALL_NOP_BYTE; fi`;
> +  link_info.separate_code = `if test "x${DEFAULT_SEPARATE_CODE}" = xyes ; then echo TRUE ; else echo FALSE ; fi`;
>    link_info.check_relocs_after_open_input = TRUE;
>    link_info.relro = DEFAULT_LD_Z_RELRO;
>  }
>