linux-kernel - Re: kexec, x86/purgatory: Cleanup the unholy mess

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Date:   Fri, 10 Mar 2017 10:05:30 -0500
From:   Vivek Goyal <vgoyal@...hat.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Mike Galbraith <efault@....de>, Borislav Petkov <bp@...en8.de>,
        "Tobin C. Harding" <me@...in.cc>,
        LKML <linux-kernel@...r.kernel.org>,
        Nicholas Mc Guire <der.herr@...r.at>, x86@...nel.org,
        Dave Young <dyoung@...hat.com>, Baoquan He <bhe@...hat.com>
Subject: Re: kexec, x86/purgatory: Cleanup the unholy mess

On Fri, Mar 10, 2017 at 03:58:20PM +0100, Thomas Gleixner wrote:
> On Fri, 10 Mar 2017, Vivek Goyal wrote:
> > I think we probably will have to initialize these global variables in
> > purgatory itself and that puts them in .data section and relocation
> > works.
> > 
> > That's how the code was intially. I initialized value of
> > purgatory_sha256_digest in the code and then did "readelf -a purgatory.o"
> > and symbol section index changed from COM to 3.
> > 
> > 13: 0000000000000000    32 OBJECT  GLOBAL DEFAULT    3
> > purgatory_sha256_digest
> > 
> > [ 3] .data             PROGBITS         0000000000000000  00000120
> >          0000000000000020  0000000000000000  WA       0     0     32
> 
> Yeah, and then instead of doing it proper you relied on compiler/link magic
> which is unreliable, undocumented and uncomprehensible. But that's just
> compatible to the rest of kexec. Works for me is never a good engineering
> principle.

Agreed. That was not a very good idea. Thanks for fixing this.

Vivek