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

From: Nicholas Piggin <[email-masked]>
Date: Fri, 20 Apr 2018 17:34:14 +1000

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 <[email-masked]>
---
 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