From: Paul Burton <paul.burton@mips.com>
Date: Wed, 21 Nov 2018 21:56:36 +0000 (+0000)
Subject: MIPS: Enable dead code elimination
X-Git-Url: http://git.lede-project.org./?a=commitdiff_plain;h=c0436b503591f927f326457a588c461881260276;p=openwrt%2Fstaging%2Fblogic.git

MIPS: Enable dead code elimination

Select CONFIG_HAVE_LD_DEAD_CODE_DATA_ELIMINATION for MIPS, allowing the
user to enable dead code elimination. In order for this to work, ensure
that we keep the data bus exception table & the machine list by
annotating them with KEEP.

This shrinks both 32r2el_defconfig & 64r6el_defconfig builds by ~6%, as
shown by numbers from scripts/bloat-o-meter:

          | 32r2el_defconfig | 64r6el_defconfig
  --------|------------------|------------------
   No DCE | 8919864          | 8286307
      DCE | 8338988 (-6.51%) | 7741808 (-6.57%)

Signed-off-by: Paul Burton <paul.burton@mips.com>
Patchwork: https://patchwork.linux-mips.org/patch/21187/
Cc: linux-mips@linux-mips.org
---

diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
index e83a8cce41e9..e49b5a0c8585 100644
--- a/arch/mips/Kconfig
+++ b/arch/mips/Kconfig
@@ -63,6 +63,7 @@ config MIPS
 	select HAVE_IRQ_TIME_ACCOUNTING
 	select HAVE_KPROBES
 	select HAVE_KRETPROBES
+	select HAVE_LD_DEAD_CODE_DATA_ELIMINATION
 	select HAVE_MEMBLOCK_NODE_MAP
 	select HAVE_MOD_ARCH_SPECIFIC
 	select HAVE_NMI
diff --git a/arch/mips/kernel/vmlinux.lds.S b/arch/mips/kernel/vmlinux.lds.S
index 971a504001c2..cb7e9ed7a453 100644
--- a/arch/mips/kernel/vmlinux.lds.S
+++ b/arch/mips/kernel/vmlinux.lds.S
@@ -72,7 +72,7 @@ SECTIONS
 	/* Exception table for data bus errors */
 	__dbe_table : {
 		__start___dbe_table = .;
-		*(__dbe_table)
+		KEEP(*(__dbe_table))
 		__stop___dbe_table = .;
 	}
 
@@ -123,7 +123,7 @@ SECTIONS
 	. = ALIGN(4);
 	.mips.machines.init : AT(ADDR(.mips.machines.init) - LOAD_OFFSET) {
 		__mips_machines_start = .;
-		*(.mips.machines.init)
+		KEEP(*(.mips.machines.init))
 		__mips_machines_end = .;
 	}