linux-kernel - Re: [RFC PATCH 00/10] x86: undwarf unwinder

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Message-ID: <20170601060824.wv2go3adbvx5ptmt@gmail.com>
Date:   Thu, 1 Jun 2017 08:08:24 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        live-patching@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andy Lutomirski <luto@...nel.org>, Jiri Slaby <jslaby@...e.cz>,
        "H. Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [RFC PATCH 00/10] x86: undwarf unwinder

* Josh Poimboeuf <jpoimboe@...hat.com> wrote:

> Here's the contents of the undwarf.txt file which explains the 'why' in
> more detail:

Ok, so the code quality looks pretty convincing to me - the new core 'undwarf' 
unwinder code is a _lot_ more readable than any of the Dwarf based attempts 
before.

That we control the debug info generation at build time is icing on the cake to 
me.

One thing I'd like to see on the list of benefits side of the equation is a size 
comparison of kernel .text, with frame pointers vs. undwarf, on 64-bit kernels.

Being able to generate more optimal code in the hottest code paths of the kernel 
is the _real_, primary upstream kernel benefit of a different debuginfo method - 
which has to be weighed against the pain of introducing a new unwinder. But this 
submission does not talk about that aspect at all, which should be fixed I think.

Thanks,

	Ingo