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

From: Adrian Bunk (bunk_at_fs.tum.de)
Date: 09/27/03

  • Next message: Jan-Benedict Glaw: "Re: [0/4] [2.6 patch] better i386 CPU selection" 
    Date:	Sat, 27 Sep 2003 00:36:12 +0200
To: Andrew Morton <akpm@osdl.org>, linux-kernel@vger.kernel.org, Yoshinori Sato <ysato@users.sourceforge.jp>

    On Thu, Sep 25, 2003 at 08:11:27PM +0200, Sam Ravnborg wrote:
    > On Thu, Sep 25, 2003 at 04:38:45PM +0200, Adrian Bunk wrote:
    > > --- linux-2.6.0-test5-mm4/init/Kconfig.old 2003-09-25 14:38:18.000000000 +0200
    > > +++ linux-2.6.0-test5-mm4/init/Kconfig 2003-09-25 14:47:12.000000000 +0200
    > > @@ -65,6 +65,16 @@
    > >
    > > menu "General setup"
    > >
    > > +config OPTIMIZE_FOR_SIZE
    > > + bool "Optimize for size" if EXPERIMENTAL
    > > + default y if ARM || H8300
    > > + default n
    > > + help
    > > + Enabling this option will pass "-Os" instead of "-O2" to gcc
    > > + resulting in a smaller kernel.
    > > +
    > > + If unsure, say N.
    > > +
    >
    > This is a general file, and it is wrong to include architecture specific
    > knowledge here.
    > I recall that Roman Zippel introduced "enable" for exactly this purpose.
    >...

    I can't see how this would help in this situation, we need a default,
    not a dependency (OPTIMIZE_FOR_SIZE=n should be possible on ARM).

    It's not the only option that sets defaults depending on the
    architecture and I can't see why it should be a bad thing.

    > Another comment about the naming of the config symbol.
    > We keep getting more config symbols controlling options to GCC.
    > A naming scheme like: CONFIG_CC_OPTIMIZE_FOR_SIZE, CONFIG_CC_DEBUG_INFO
    > is preferable since it give better context information.
    > Let's start with this option, and rename the others later.

    Below is the patch with CONFIG_CC_OPTIMIZE_FOR_SIZE.

    > Sam

    cu
    Adrian

    --- linux-2.6.0-test5-mm4/init/Kconfig.old 2003-09-25 14:38:18.000000000 +0200
    +++ linux-2.6.0-test5-mm4/init/Kconfig 2003-09-25 14:47:12.000000000 +0200
    @@ -65,6 +65,16 @@
     
     menu "General setup"
     
    +config CC_OPTIMIZE_FOR_SIZE
    + bool "Optimize for size" if EXPERIMENTAL
    + default y if ARM || H8300
    + 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-test5-mm4/Makefile.old 2003-09-25 14:38:18.000000000 +0200
    +++ linux-2.6.0-test5-mm4/Makefile 2003-09-25 14:40:26.000000000 +0200
    @@ -274,7 +274,7 @@
     CPPFLAGS := -D__KERNEL__ -Iinclude \
                        $(if $(KBUILD_SRC),-Iinclude2 -I$(srctree)/include)
     
    -CFLAGS := -Wall -Wstrict-prototypes -Wno-trigraphs -O2 \
    +CFLAGS := -Wall -Wstrict-prototypes -Wno-trigraphs \
                          -fno-strict-aliasing -fno-common
     AFLAGS := -D__ASSEMBLY__
     
    @@ -421,6 +421,12 @@
     # ---------------------------------------------------------------------------
     
     
    +ifdef CONFIG_CC_OPTIMIZE_FOR_SIZE
    +CFLAGS += -Os
    +else
    +CFLAGS += -O2
    +endif
    +
     ifndef CONFIG_FRAME_POINTER
     CFLAGS += -fomit-frame-pointer
     endif
    --- linux-2.6.0-test5-mm4/arch/arm/Makefile.old 2003-09-25 14:38:18.000000000 +0200
    +++ linux-2.6.0-test5-mm4/arch/arm/Makefile 2003-09-25 14:40:47.000000000 +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-test5-mm4/arch/h8300/Kconfig.old 2003-09-25 14:43:27.000000000 +0200
    +++ linux-2.6.0-test5-mm4/arch/h8300/Kconfig 2003-09-25 14:43:44.000000000 +0200
    @@ -5,6 +5,10 @@
     
     mainmenu "uClinux/h8300 (w/o MMU) Kernel Configuration"
     
    +config H8300
    + bool
    + default y
    +
     config MMU
             bool
             default n
    --- linux-2.6.0-test5-mm4/arch/h8300/Makefile.old 2003-09-25 14:38:18.000000000 +0200
    +++ linux-2.6.0-test5-mm4/arch/h8300/Makefile 2003-09-25 14:38:24.000000000 +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\"
    -
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