linux-kernel - Re: [PATCH] static_call: Use single copy of static_call

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Message-ID: <YIZ2/2H4W1U5DNBm@hirez.programming.kicks-ass.net>
Date:   Mon, 26 Apr 2021 10:17:03 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Andi Kleen <ak@...ux.intel.com>
Cc:     jpoimboe@...hat.com, jbaron@...mai.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] static_call: Use single copy of static_call_return0

On Sun, Apr 25, 2021 at 02:11:40PM -0700, Andi Kleen wrote:
> With the inline version of static calls it is trying to use
> all static call functions inline. But this doesn't work for
> __static_call_return0, because its address is always taken,
> which forces the compiler to generate a out of line copy.
> 
> If it only exists as a static inline this means there are
> many copies generated. Instead use the out of line in static_call.c
> for this.
> 
> This fixes another bug. When _INLINE is set static_inline.c was
> not compiled at all, which disabled the self test even when
> it was enabled in the configuration.
> 
> This fixes a build problem with gcc LTO. __static_call_return0
> is referenced from assembler, which requires making it global
> because the assembler can end in a different file than the other
> C code.  But that's not possible for a static inline function.

This is ARCH=i386 only afaict, why do we care?