[2.6 patch] add a config option for -Os

[2.6 patch] add a config option for -Os

[Adrian Bunk]

The patch below adds a config option for compiling the kernel with -Os.

Compared to the last patch, the option moved to the embedded to the 
General Setup menu and depends on EXPERIMENTAL instead of EMBEDDED 
(retionale: it might even produce a faster kernel but it's less tested).

I removed the special cases in the arm, arm26 and h8300 Makefiles, users 
on these architectures can now use OPTIMIZE_FOR_SIZE.

Compiling with this option enabled produced a working kernel for me on 
i386.

cu
Adrian

--- linux-2.6.0-test4/init/Kconfig.old	2003-08-24 14:51:15.000000000 +0200
+++ linux-2.6.0-test4/init/Kconfig	2003-08-24 14:55:45.000000000 +0200
@@ -48,6 +48,15 @@
 
 menu "General setup"
 
+config OPTIMIZE_FOR_SIZE
+	bool "Optimize for size" if EXPERIMENTAL
+	default n
+	help
+	  Enabling this option will pass "-Os" instead of "-O2" to gcc
+	  resulting in a smaller kernel.
+
+	  If unsure, say N.
+
 config SWAP
 	bool "Support for paging of anonymous memory"
 	depends on MMU
--- linux-2.6.0-test3/Makefile.old	2003-08-11 01:34:41.000000000 +0200
+++ linux-2.6.0-test3/Makefile	2003-08-11 01:37:16.000000000 +0200
@@ -223,7 +223,7 @@
 NOSTDINC_FLAGS  = -nostdinc -iwithprefix include
 
 CPPFLAGS	:= -D__KERNEL__ -Iinclude
-CFLAGS 		:= -Wall -Wstrict-prototypes -Wno-trigraphs -O2 \
+CFLAGS 		:= -Wall -Wstrict-prototypes -Wno-trigraphs \
 	  	   -fno-strict-aliasing -fno-common
 AFLAGS		:= -D__ASSEMBLY__
 
@@ -318,6 +318,12 @@
 
 -include .config.cmd
 
+ifdef CONFIG_OPTIMIZE_FOR_SIZE
+CFLAGS		+= -Os
+else
+CFLAGS		+= -O2
+endif
+
 ifndef CONFIG_FRAME_POINTER
 CFLAGS		+= -fomit-frame-pointer
 endif
--- linux-2.6.0-test4/arch/arm26/Makefile.old	2003-08-24 14:50:45.000000000 +0200
+++ linux-2.6.0-test4/arch/arm26/Makefile	2003-08-24 14:56:15.000000000 +0200
@@ -13,7 +13,6 @@
 OBJCOPYFLAGS	:=-O binary -R .note -R .comment -S
 GZFLAGS		:=-9
 #CFLAGS		+=-pipe
-CFLAGS		:=$(CFLAGS:-O2=-Os)
 
 ifeq ($(CONFIG_FRAME_POINTER),y)
 CFLAGS		+=-fno-omit-frame-pointer -mno-sched-prolog
--- linux-2.6.0-test4/arch/arm/Makefile.old	2003-08-24 14:56:41.000000000 +0200
+++ linux-2.6.0-test4/arch/arm/Makefile	2003-08-24 14:56:57.000000000 +0200
@@ -14,8 +14,6 @@
 GZFLAGS		:=-9
 #CFLAGS		+=-pipe
 
-CFLAGS		:=$(CFLAGS:-O2=-Os)
-
 ifeq ($(CONFIG_FRAME_POINTER),y)
 CFLAGS		+=-fno-omit-frame-pointer -mapcs -mno-sched-prolog
 endif
--- linux-2.6.0-test4/arch/h8300/Makefile.old	2003-08-24 14:59:42.000000000 +0200
+++ linux-2.6.0-test4/arch/h8300/Makefile	2003-08-24 15:00:18.000000000 +0200
@@ -34,7 +34,7 @@
 ldflags-$(CONFIG_CPU_H8S)	:= -mh8300self
 
 CFLAGS += $(cflags-y)
-CFLAGS += -mint32 -fno-builtin -Os
+CFLAGS += -mint32 -fno-builtin
 CFLAGS += -g
 CFLAGS += -D__linux__
 CFLAGS += -DUTS_SYSNAME=\"uClinux\"

Re: [2.6 patch] add a config option for -Os

[Yoshinori Sato]

At Tue, 26 Aug 2003 00:47:17 +0200,
Adrian Bunk wrote:
> 
> The patch below adds a config option for compiling the kernel with -Os.
> 
> Compared to the last patch, the option moved to the embedded to the 
> General Setup menu and depends on EXPERIMENTAL instead of EMBEDDED 
> (retionale: it might even produce a faster kernel but it's less tested).
> 
> I removed the special cases in the arm, arm26 and h8300 Makefiles, users 
> on these architectures can now use OPTIMIZE_FOR_SIZE.
> 
> Compiling with this option enabled produced a working kernel for me on 
> i386.
> 

An idea do not change -O2, and to add specification of -Os to with "OPTIMIZE_SIZE" ?
If there are a few the ones, degradation of speed means.

vmlinux  size of h8300
        -O2     -Os   -O2&-Os
.text  561200  554368  555088
.data   59148   58612   58868
.bss    45244   45260   45244
total  665592  658240  659200

-- 
Yoshinori Sato
<ysato@users.sourceforge.jp>

Re: [2.6 patch] add a config option for -Os

[Valdis.Kletnieks]

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On Tue, 26 Aug 2003 23:41:09 +0900, Yoshinori Sato said:

>         -O2     -Os   -O2&-Os
> .text  561200  554368  555088
> .data   59148   58612   58868
> .bss    45244   45260   45244
> total  665592  658240  659200

Note that specifying -O2 *and* -Os together is probably counter-productive.

'info gcc' says:

    If you use multiple `-O' options, with or without level numbers,
     the last such option is the one that is effective.

You might want to investigate why the 3rd column of numbers is different
from both of the first two.


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