RFC: x86: Enable -z separate-code by default
Michael Matz
matz@suse.de
Mon Feb 19 15:53:00 GMT 2018
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;
> }
>
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