[PATCH 4/4] powerpc: Allow LD_DEAD_CODE_DATA_ELIMINATION to be selected

[Mathieu Malaterre]

On Fri, Apr 20, 2018 at 9:34 AM, Nicholas Piggin <npiggin at gmail.com> wrote:
> This requires further changes to linker script to KEEP some tables
> and wildcard compiler generated sections into the right place. This
> includes pp32 modifications from Christophe Leroy.
>
> When compiling powernv_defconfig with this option:
>
> text       data      bss       dec        filename
> 11827621   4810490   1341080   17979191   vmlinux
> 11752437   4598858   1338776   17690071   vmlinux.dcde
>
> Resulting kernel is almost 400kB smaller (and still boots).
>
> [ppc32 numbers here]

^^^

Do you want somebody else to provide those numbers ?

> Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
> ---
>  arch/powerpc/Kconfig              |  1 +
>  arch/powerpc/kernel/vmlinux.lds.S | 22 +++++++++++-----------
>  2 files changed, 12 insertions(+), 11 deletions(-)
>
> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> index c32a181a7cbb..ee6dbe2efc8b 100644
> --- a/arch/powerpc/Kconfig
> +++ b/arch/powerpc/Kconfig
> @@ -205,6 +205,7 @@ config PPC
>         select HAVE_KPROBES
>         select HAVE_KPROBES_ON_FTRACE
>         select HAVE_KRETPROBES
> +       select HAVE_LD_DEAD_CODE_DATA_ELIMINATION
>         select HAVE_LIVEPATCH                   if HAVE_DYNAMIC_FTRACE_WITH_REGS
>         select HAVE_MEMBLOCK
>         select HAVE_MEMBLOCK_NODE_MAP
> diff --git a/arch/powerpc/kernel/vmlinux.lds.S b/arch/powerpc/kernel/vmlinux.lds.S
> index c8af90ff49f0..89381dc959ce 100644
> --- a/arch/powerpc/kernel/vmlinux.lds.S
> +++ b/arch/powerpc/kernel/vmlinux.lds.S
> @@ -89,7 +89,7 @@ SECTIONS
>          */
>         .text BLOCK(0) : AT(ADDR(.text) - LOAD_OFFSET) {
>  #ifdef CONFIG_LD_HEAD_STUB_CATCH
> -               *(.linker_stub_catch);
> +               KEEP(*(.linker_stub_catch));
>                 . = . ;
>  #endif
>
> @@ -98,7 +98,7 @@ SECTIONS
>                 ALIGN_FUNCTION();
>  #endif
>                 /* careful! __ftr_alt_* sections need to be close to .text */
> -               *(.text.hot .text .text.fixup .text.unlikely .fixup __ftr_alt_* .ref.text);
> +               *(.text.hot .text .text.[0-9a-zA-Z_]* .text.fixup .text.unlikely .fixup __ftr_alt_* .ref.text);
>                 SCHED_TEXT
>                 CPUIDLE_TEXT
>                 LOCK_TEXT
> @@ -170,10 +170,10 @@ SECTIONS
>         .init.data : AT(ADDR(.init.data) - LOAD_OFFSET) {
>                 INIT_DATA
>                 __vtop_table_begin = .;
> -               *(.vtop_fixup);
> +               KEEP(*(.vtop_fixup));
>                 __vtop_table_end = .;
>                 __ptov_table_begin = .;
> -               *(.ptov_fixup);
> +               KEEP(*(.ptov_fixup));
>                 __ptov_table_end = .;
>         }
>
> @@ -194,26 +194,26 @@ SECTIONS
>         . = ALIGN(8);
>         __ftr_fixup : AT(ADDR(__ftr_fixup) - LOAD_OFFSET) {
>                 __start___ftr_fixup = .;
> -               *(__ftr_fixup)
> +               KEEP(*(__ftr_fixup))
>                 __stop___ftr_fixup = .;
>         }
>         . = ALIGN(8);
>         __mmu_ftr_fixup : AT(ADDR(__mmu_ftr_fixup) - LOAD_OFFSET) {
>                 __start___mmu_ftr_fixup = .;
> -               *(__mmu_ftr_fixup)
> +               KEEP(*(__mmu_ftr_fixup))
>                 __stop___mmu_ftr_fixup = .;
>         }
>         . = ALIGN(8);
>         __lwsync_fixup : AT(ADDR(__lwsync_fixup) - LOAD_OFFSET) {
>                 __start___lwsync_fixup = .;
> -               *(__lwsync_fixup)
> +               KEEP(*(__lwsync_fixup))
>                 __stop___lwsync_fixup = .;
>         }
>  #ifdef CONFIG_PPC64
>         . = ALIGN(8);
>         __fw_ftr_fixup : AT(ADDR(__fw_ftr_fixup) - LOAD_OFFSET) {
>                 __start___fw_ftr_fixup = .;
> -               *(__fw_ftr_fixup)
> +               KEEP(*(__fw_ftr_fixup))
>                 __stop___fw_ftr_fixup = .;
>         }
>  #endif
> @@ -226,7 +226,7 @@ SECTIONS
>         . = ALIGN(8);
>         .machine.desc : AT(ADDR(.machine.desc) - LOAD_OFFSET) {
>                 __machine_desc_start = . ;
> -               *(.machine.desc)
> +               KEEP(*(.machine.desc))
>                 __machine_desc_end = . ;
>         }
>  #ifdef CONFIG_RELOCATABLE
> @@ -274,7 +274,7 @@ SECTIONS
>         .data : AT(ADDR(.data) - LOAD_OFFSET) {
>                 DATA_DATA
>                 *(.data.rel*)
> -               *(.sdata)
> +               *(SDATA_MAIN)
>                 *(.sdata2)
>                 *(.got.plt) *(.got)
>                 *(.plt)
> @@ -289,7 +289,7 @@ SECTIONS
>
>         .opd : AT(ADDR(.opd) - LOAD_OFFSET) {
>                 __start_opd = .;
> -               *(.opd)
> +               KEEP(*(.opd))
>                 __end_opd = .;
>         }
>
> --
> 2.17.0
>