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Date: Tue, 20 Mar 2018 11:41:26 -0700
From: "Luck, Tony" <tony.luck@intel.com>
Subject: Re: [linux-next:master] BUILD REGRESSION
 a5444cde9dc2120612e50fc5a56c975e67a041fb
Message-ID: <20180320184125.jy4w4cfzgeavwt5p@agluck-desk>
References: <5ab048c0.wmRYTJi5ip8zBzJ4%fengguang.wu@intel.com>
 <d22bd482-2f5b-8c02-4821-9f1b02122b51@infradead.org>
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To: Randy Dunlap <rdunlap@infradead.org>
Cc: kbuild test robot <fengguang.wu@intel.com>, Andrew Morton <akpm@linux-foundation.org>, Linux Memory Management List <linux-mm@kvack.org>

On Mon, Mar 19, 2018 at 06:10:13PM -0700, Randy Dunlap wrote:
> On 03/19/2018 04:33 PM, kbuild test robot wrote:
> > tree/branch: https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git  master
> > branch HEAD: a5444cde9dc2120612e50fc5a56c975e67a041fb  Add linux-next specific files for 20180319
> > 
> > Regressions in current branch:
> > 
> > ERROR: "__sw_hweight8" [drivers/net/wireless/mediatek/mt76/mt76.ko] undefined!
> 
> Well, the driver could do:
> 
> drivers/net/wireless/mediatek/mt76/Kconfig:
> 
> +	select GENERIC_HWEIGHT
> 
> but maybe arch/ix64/Kconfig (where the build error is) could be asked to do:
> 
> config GENERIC_HWEIGHT
> 	def_bool y
> 
> like 23 other $arch-es do.  Aha, ia64 provides inline functions via some
> a twisty maze of header files.
> 
> Tony, Fengguang, what header(s) should be used to reach __arch_hweight8()?

Looks like a few architectures have their own __arch_hweight8
(alpha, blackfin, ia64, mips, powerpc, sparc, tile and x86)

everyone except x86 puts them in <asm/bitops.h> ... x86 has a
<asm/arch_hweight.h>

Likely that the best solution would be to match how x86 does
this and move the hweight defines out of bitops.h.  But it all
seems very messy :-(

-Tony