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

Nicholas Piggin
2018-04-20T07:34:46Z

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 <npiggin@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