linux-kernel - Re: [RFC][PATCH v3 1/5] sparc64: Fix asm/percpu.h build error

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Message-ID: <20200604165703.GG3976@hirez.programming.kicks-ass.net>
Date:   Thu, 4 Jun 2020 18:57:03 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     David Miller <davem@...emloft.net>
Cc:     mingo@...nel.org, will@...nel.org, tglx@...utronix.de,
        x86@...nel.org, linux-kernel@...r.kernel.org,
        a.darwish@...utronix.de, rostedt@...dmis.org,
        bigeasy@...utronix.de, sparclinux@...r.kernel.org,
        mpe@...erman.id.au, linuxppc-dev@...ts.ozlabs.org,
        heiko.carstens@...ibm.com, linux-s390@...r.kernel.org
Subject: Re: [RFC][PATCH v3 1/5] sparc64: Fix asm/percpu.h build error

On Fri, May 29, 2020 at 04:29:17PM -0700, David Miller wrote:
> From: Peter Zijlstra <peterz@...radead.org>
> Date: Fri, 29 May 2020 23:35:51 +0200
> 
> > ../arch/sparc/include/asm/percpu_64.h:7:24: warning: call-clobbered register used for global register variable
> > register unsigned long __local_per_cpu_offset asm("g5");
> 
> The "-ffixed-g5" option on the command line tells gcc that we are
> using 'g5' as a fixed register, so some part of your build isn't using
> the:
> 
> KBUILD_CFLAGS += -ffixed-g4 -ffixed-g5 -fcall-used-g7 -Wno-sign-compare
> 
> from arch/sparc/Makefile for some reason.

Thanks, that was the clue I needed.

I think I see, what happens is that these headers end up in the VDSO
build, and that doesn't have these CFLAGS, because userspace.

Let me see what to do about that.