linux-kernel - Re: [PATCH 2/5] bitops: compile time optimization for hweight

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Date:	Thu, 18 Feb 2010 07:19:23 +0100
From:	Borislav Petkov <petkovbb@...glemail.com>
To:	Michal Marek <mmarek@...e.cz>
Cc:	Borislav Petkov <bp@...64.org>, "H. Peter Anvin" <hpa@...or.com>,
	linux-kbuild <linux-kbuild@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Wu Fengguang <fengguang.wu@...el.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Jamie Lokier <jamie@...reable.org>,
	Roland Dreier <rdreier@...co.com>,
	Al Viro <viro@...IV.linux.org.uk>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>, Brian Gerst <brgerst@...il.com>
Subject: Re: [PATCH 2/5] bitops: compile time optimization for
 hweight_long(CONSTANT)

On Wed, Feb 17, 2010 at 06:39:13PM +0100, Michal Marek wrote:
> It wouldn't work actually, because such variable would then apply to all
> hweight.o targets in the tree. But another way would be:
> 
> arch/x86/Kconfig
> config ARCH_HWEIGHT_CFLAGS
>         string
>         default "..." if X86_32
>         default "..." if X86_64
> 
> lib/Makefile
> CFLAGS_hweight.o = $(CONFIG_ARCH_HWEIGHT_CFLAGS)

Yep, this works, albeit with a small adjustment since
CONFIG_ARCH_HWEIGHT_CFLAGS is quoted in the Kconfig and the quotes
appear in the $(CC) call like this:

gcc -Wp,-MD,lib/.hweight.o.d  ... "-fcall-saved-ecx..."

which I fixed like this (idea reused from the make manual):

---
 source "init/Kconfig"
diff --git a/lib/Makefile b/lib/Makefile
index 3b0b4a6..e2ad17c 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -39,7 +39,10 @@ lib-$(CONFIG_RWSEM_XCHGADD_ALGORITHM) += rwsem.o
 lib-$(CONFIG_GENERIC_FIND_FIRST_BIT) += find_next_bit.o
 lib-$(CONFIG_GENERIC_FIND_NEXT_BIT) += find_next_bit.o
 obj-$(CONFIG_GENERIC_FIND_LAST_BIT) += find_last_bit.o
+
+CFLAGS_hweight.o = $(subst $(quote),,$(CONFIG_ARCH_HWEIGHT_CFLAGS))
 obj-$(CONFIG_GENERIC_HWEIGHT) += hweight.o
+
 obj-$(CONFIG_LOCK_KERNEL) += kernel_lock.o
 obj-$(CONFIG_DEBUG_PREEMPT) += smp_processor_id.o
 obj-$(CONFIG_DEBUG_LIST) += list_debug.o
diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index f9bdf26..cbcd654 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -245,3 +245,7 @@ quiet_cmd_lzo = LZO    $@
 cmd_lzo = (cat $(filter-out FORCE,$^) | \
 	lzop -9 && $(call size_append, $(filter-out FORCE,$^))) > $@ || \
 	(rm -f $@ ; false)
+
+# misc stuff
+# ---------------------------------------------------------------------------
+quote:="



I'm open for better suggestions though.

-- 
Regards/Gruss,
    Boris.
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