linux-kernel - Re: arch/mips/include/asm/checksum.h:195:9: error: unsupported inline asm: input with type 'unsigned long' matching output with type '_

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Date:   Sun, 22 May 2022 21:48:52 +0100 (BST)
From:   "Maciej W. Rozycki" <macro@...am.me.uk>
To:     Nathan Chancellor <nathan@...nel.org>
cc:     Paul Cercueil <paul@...pouillou.net>,
        kernel test robot <lkp@...el.com>, llvm@...ts.linux.dev,
        kbuild-all@...ts.01.org, linux-kernel@...r.kernel.org,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        linux-mips <linux-mips@...r.kernel.org>
Subject: Re: arch/mips/include/asm/checksum.h:195:9: error: unsupported inline
 asm: input with type 'unsigned long' matching output with type '__wsum' (aka
 'unsigned int')

On Fri, 20 May 2022, Nathan Chancellor wrote:

> >  It doesn't matter whether there is ADDU or DADDU anymore, given that 
> > commit 198688edbf77 ("MIPS: Fix inline asm input/output type mismatch in 
> > checksum.h used with Clang") has added a redundant 32-bit sign-extension 
> > operation right afterwards, regressing size/performance by an extra 
> > instruction in this performance-critical code as a workaround for a stupid 
> > compiler.
> 
> Shouldn't this concern have been addressed by Tiezhu's follow up?
> 
> https://lore.kernel.org/1617359240-16609-1-git-send-email-yangtiezhu@loongson.cn/
> 
> I guess it never got picked up?

 Still it is a hack.  I have now rewritten this code in plain C instead.

  Maciej