linux-kernel - Re: linux-next: build failure after merge of the vfs tree

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Date:   Tue, 6 Oct 2020 09:30:12 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     Stephen Rothwell <sfr@...b.auug.org.au>,
        Linux Next Mailing List <linux-next@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...e.de>
Subject: Re: linux-next: build failure after merge of the vfs tree

On Mon, Sep 28, 2020 at 11:10:56PM -0500, Josh Poimboeuf wrote:
> > Josh, any ideas?  We could, of course, make it "r"(size), but that would
> > be unpleasant in all existing callers...
> 
> Sorry, I've been traveling.  I'd just vote for making it "r".
> 
> array_index_nospec() is always called after a usercopy.  I don't think
> anyone will notice the extra mov, for the cases where it would be
> propagated as an immediate.  And the argument *is* an unsigned long
> after all.
> 
> Stephen, can you confirm this fixes it?

Still traveling, I didn't see an update on this.  Any objections to the
below?  I assume it fixes Stephen's build issue.

> 
> diff --git a/arch/x86/include/asm/barrier.h b/arch/x86/include/asm/barrier.h
> index d158ea1fa250..69045ac62f58 100644
> --- a/arch/x86/include/asm/barrier.h
> +++ b/arch/x86/include/asm/barrier.h
> @@ -40,7 +40,7 @@ static inline unsigned long array_index_mask_nospec(unsigned long index,
>  
>  	asm volatile ("cmp %1,%2; sbb %0,%0;"
>  			:"=r" (mask)
> -			:"g"(size),"r" (index)
> +			:"r"(size), "r"(index)
>  			:"cc");
>  	return mask;
>  }
> 

-- 
Josh