From: Andi Kleen , me. Using -mregparm=3 shrinks the kernel further: (compiled with gcc 3.4, without -funit-at-a-time, using the later and together with -Os shrinks .text even more, making over 700KB difference) 4129346 708629 207240 5045215 4cfbdf vmlinux 3892905 708629 207240 4808774 496046 vmlinux-regparm This one helps even more, >236KB .text difference. Clearly worth the effort. This patch adds an option to use -mregparm=3 while compiling the kernel. I did an LTP run and it showed no additional failures over an non regparm kernel. According to some gcc developers it should be safe to use in all gccs that are still supports (2.95 and up) I didn't make it the default because it will break all binary only modules (although they can be fixed by adding a wrapper that calls them with "asmlinkage"). Actually it may be a good idea to make this default with 2.7.1 or somesuch. We add new kbuild infrastructure: the command scripts/gcc-version.sh $(CC) will print out the version of gcc in a canonical 4-digit form suitable for performing numerical tests against. DESC arch/i386/Makefile,scripts/gcc-version.sh,Makefile small fixes EDESC From: Serge Belyshev <33554432@mtu-net.ru> arch/i386/Makefile: * omitted $(KBUILD_SRC)/ in script call. scripts/gcc-version.sh: * GNU tail no longer supports 'tail -1' syntax. We should consider adding -fweb option: vanilla: $ size vmlinux text data bss dec hex filename 3056270 526780 386056 3969106 3c9052 vmlinux with -fweb: $ size vmlinux text data bss dec hex filename 3049523 526780 386056 3962359 3c75f7 vmlinux Also note 0.1 ... 1.0% speedup in various benchmarks. This option is not enabled by default at -O2 because it (like -fomit-frame-pointer) makes debugging impossible. --- arch/i386/Kconfig | 13 +++++++++++++ arch/i386/Makefile | 5 +++++ include/asm-i386/module.h | 8 +++++++- scripts/gcc-version.sh | 14 ++++++++++++++ 4 files changed, 39 insertions(+), 1 deletion(-) diff -puN arch/i386/Kconfig~add-config-for-mregparm-3-ng arch/i386/Kconfig --- 25/arch/i386/Kconfig~add-config-for-mregparm-3-ng 2004-02-13 22:12:42.000000000 -0800 +++ 25-akpm/arch/i386/Kconfig 2004-02-13 22:12:42.000000000 -0800 @@ -850,6 +850,19 @@ config BOOT_IOREMAP depends on (((X86_SUMMIT || X86_GENERICARCH) && NUMA) || (X86 && EFI)) default y +config REGPARM + bool "Use register arguments (EXPERIMENTAL)" + depends on EXPERIMENTAL + default n + help + Compile the kernel with -mregparm=3. This uses an different ABI + and passes the first three arguments of a function call in registers. + This will probably break binary only modules. + + This feature is only enabled for gcc-3.0 and later - earlier compilers + generate incorrect output with certain kernel constructs when + -mregparm=3 is used. + endmenu diff -puN arch/i386/Makefile~add-config-for-mregparm-3-ng arch/i386/Makefile --- 25/arch/i386/Makefile~add-config-for-mregparm-3-ng 2004-02-13 22:12:42.000000000 -0800 +++ 25-akpm/arch/i386/Makefile 2004-02-13 22:12:42.000000000 -0800 @@ -51,6 +51,11 @@ cflags-$(CONFIG_MVIAC3_2) += $(call chec # AMD Elan support cflags-$(CONFIG_X86_ELAN) += -march=i486 +# -mregparm=3 works ok on gcc-3.0 and later +# +GCC_VERSION := $(shell $(CONFIG_SHELL) $(srctree)/scripts/gcc-version.sh $(CC)) +cflags-$(CONFIG_REGPARM) += $(shell if [ $(GCC_VERSION) -ge 0300 ] ; then echo "-mregparm=3"; fi ;) + CFLAGS += $(cflags-y) # Default subarch .c files diff -puN include/asm-i386/module.h~add-config-for-mregparm-3-ng include/asm-i386/module.h --- 25/include/asm-i386/module.h~add-config-for-mregparm-3-ng 2004-02-13 22:12:42.000000000 -0800 +++ 25-akpm/include/asm-i386/module.h 2004-02-13 22:12:42.000000000 -0800 @@ -54,6 +54,12 @@ struct mod_arch_specific #define MODULE_PROC_FAMILY "this needs to be fixed" #endif -#define MODULE_ARCH_VERMAGIC MODULE_PROC_FAMILY +#ifdef CONFIG_REGPARM +#define MODULE_REGPARM "REGPARM " +#else +#define MODULE_REGPARM "" +#endif + +#define MODULE_ARCH_VERMAGIC MODULE_PROC_FAMILY MODULE_REGPARM #endif /* _ASM_I386_MODULE_H */ diff -puN /dev/null scripts/gcc-version.sh --- /dev/null 2002-08-30 16:31:37.000000000 -0700 +++ 25-akpm/scripts/gcc-version.sh 2004-02-13 22:12:42.000000000 -0800 @@ -0,0 +1,14 @@ +#!/bin/sh +# +# gcc-version gcc-command +# +# Prints the gcc version of `gcc-command' in a canonical 4-digit form +# such as `0295' for gcc-2.95, `0303' for gcc-3.3, etc. +# + +compiler="$*" + +MAJOR=$(echo __GNUC__ | $compiler -E -xc - | tail -n 1) +MINOR=$(echo __GNUC_MINOR__ | $compiler -E -xc - | tail -n 1) +printf "%02d%02d\\n" $MAJOR $MINOR + _