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SubjectRe: [PATCH] Add CONFIG for -mregparm=3
On Thu, Jan 15, 2004 at 11:40:11AM +1100, Rusty Russell wrote:
> On Wed, 14 Jan 2004 10:06:03 +0100
> Andi Kleen <ak@muc.de> wrote:
> > 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.
>
> Who cares. Anyway, if kept as a config option, this should probably be
> added to MODULE_ARCH_VERMAGIC in include/asm-i386/module.h.

Ok. Good point.

On second thought I'm actually not opposed to make it the default,
but Linus/Andrew have to decide if they want this. It certainly
would be a good strategy longer term (even though it would eliminate
some of the advantages x86-64 currently enjoys over i386 ;-)

New patch appended.

-Andi

----------------------------------------

Add CONFIG_REGPARM option to enable compilation with -mregparm=3.
This shrinks the kernel .text considerably.

This could be made default later when it has been more tested.


diff -u linux-34/arch/i386/Kconfig-o linux-34/arch/i386/Kconfig
--- linux-34/arch/i386/Kconfig-o 2004-01-09 09:27:09.000000000 +0100
+++ linux-34/arch/i386/Kconfig 2004-01-14 08:43:29.000000000 +0100
@@ -820,6 +820,14 @@
depends on (((X86_SUMMIT || X86_GENERICARCH) && NUMA) || (X86 && EFI))
default y

+config REGPARM
+ bool "Use register arguments (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.
+
endmenu


diff -u linux-34/arch/i386/Makefile-o linux-34/arch/i386/Makefile
--- linux-34/arch/i386/Makefile-o 2003-09-28 10:53:14.000000000 +0200
+++ linux-34/arch/i386/Makefile 2004-01-13 20:16:32.000000000 +0100
@@ -47,6 +47,8 @@
cflags-$(CONFIG_MCYRIXIII) += $(call check_gcc,-march=c3,-march=i486) $(align)-functions=0 $(align)-jumps=0 $(align)-loops=0
cflags-$(CONFIG_MVIAC3_2) += $(call check_gcc,-march=c3-2,-march=i686)

+cflags-$(CONFIG_REGPARM) += -mregparm=3
+
CFLAGS += $(cflags-y)

# Default subarch .c files
diff -u linux-34/include/asm-i386/module.h-o linux-34/include/asm-i386/module.h
--- linux-34/include/asm-i386/module.h-o 2003-05-27 03:00:24.000000000 +0200
+++ linux-34/include/asm-i386/module.h 2004-01-15 10:15:15.686788608 +0100
@@ -52,6 +52,12 @@
#error unknown processor family
#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 */


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