linux-kernel - Re: [GIT PULL] x86/asm changes for v5.6

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Message-ID: <20200129180012.jmncqyb7x77gkzwq@treble>
Date:   Wed, 29 Jan 2020 12:00:12 -0600
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Borislav Petkov <bp@...e.de>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        "Luck, Tony" <tony.luck@...el.com>, Ingo Molnar <mingo@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [GIT PULL] x86/asm changes for v5.6

On Tue, Jan 28, 2020 at 11:31:10PM +0100, Borislav Petkov wrote:
> On Tue, Jan 28, 2020 at 01:04:19PM -0800, Linus Torvalds wrote:
> > On Tue, Jan 28, 2020 at 12:41 PM Luck, Tony <tony.luck@...el.com> wrote:
> > >
> > > Is there still some easy way to get gdb to disassemble from /dev/kmem
> > > to see what we ended up with after all the patching?
> > 
> > Hmm. No, I think it's all gone.
> > 
> > It _used_ to be easy to just do "objdump --disassemble /proc/kcore" as
> > root, but I think we've broken that long ago.
> 
> Either booting with "debug-alternative" on baremetal or starting a guest
> and stopping it with gdb and examining the patched memory is what I've
> been using to hack on the alternatives in past years. Guest won't help
> you a whole lot with FSRM but you could "force it", for example.

FWIW, I can still do 'objdump -d' and gdb on /proc/kcore just fine
(though you have to give gdb addresses because no symbols).

-- 
Josh