linux-kernel - Re: [PATCH 4/8] s390/entry: workaround llvm's IAS limitations

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Date:   Mon, 16 May 2022 16:05:45 +0200
From:   Heiko Carstens <hca@...ux.ibm.com>
To:     Alexander Gordeev <agordeev@...ux.ibm.com>
Cc:     Nathan Chancellor <nathan@...nel.org>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Jonas Paulsson <paulsson@...ux.vnet.ibm.com>,
        Ulrich Weigand <ulrich.weigand@...ibm.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Alexander Egorenkov <egorenar@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>,
        Andreas Krebbel <krebbel@...ux.ibm.com>,
        Nathan Chancellor <natechancellor@...il.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org
Subject: Re: [PATCH 4/8] s390/entry: workaround llvm's IAS limitations

On Mon, May 16, 2022 at 01:11:48PM +0200, Alexander Gordeev wrote:
> > So I'd suggest: leave this code as is, and at some later point move
> > "rework" the early machine check handler code.
> > 
> > What do you think?
> 
> Sounds very reasonable. Please, find my:
> 
> Acked-by: Alexander Gordeev <agordeev@...ux.ibm.com>

Thanks!

> Also, how such a follow-up looks to you?
...
> 	slgfi	%r14,\start
> 	clgfi	%r14,\end - \start

I think using an address as an immediate value is a step in the wrong
direction, since I'd like to have all code pc-relative. And as far as
I can tell this new construct would only work as long as \start has an
absolute address that is low enough so that it would work / fit with
slgfi.
Of course this will likely always be the case, but I still think this
is not the way we should go.