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

[Christophe LEROY]

Le 20/04/2018 à 09:34, Nicholas Piggin a écrit :

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]

Signed-off-by: Nicholas Piggin <npig...@gmail.com>

Tested-by: Christophe Leroy <christophe.le...@c-s.fr>

Tested on MPC885 and MPC8321E, CONFIG_MODULE unset.

Christophe

---
  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 = .;
        }