linux-kernel - Re: [PATCH 7/7] DWARF: add the config option

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Message-ID: <20170520171917.6vru6sohd2wvotw3@treble>
Date:   Sat, 20 May 2017 12:19:17 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     "H. J. Lu" <hjl.tools@...il.com>, "H. Peter Anvin" <hpa@...or.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Jiri Slaby <jslaby@...e.cz>,
        Andrew Morton <akpm@...ux-foundation.org>,
        live-patching@...r.kernel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        the arch/x86 maintainers <x86@...nel.org>,
        Jiri Kosina <jikos@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 7/7] DWARF: add the config option

On Sat, May 20, 2017 at 11:20:34AM -0500, Josh Poimboeuf wrote:
>    But then, if we're going that far, why not just have objtool reformat
>    the data into something much simpler?  It already has the knowledge
>    to do so.  Then we don't have to jump through all those hoops to
>    justify jumping through more hoops in the kernel (i.e., having a
>    complex DWARF state machine).  With a simple debuginfo format, the
>    kernel unwinder is simple enough that we don't need to validate its
>    functionality in a simulator.

I should clarify that it doesn't have to be objtool which does this.  It
could instead be a simple DWARF-to-undwarf conversion tool which runs
during the vmlinux linking stage.

Anyway we're both proposing simplifying the DWARF data into an
easier-to-parse format.  I think the question is whether we want that
simplification process to happen in the kernel (in the middle of a
kernel unwind operation), or at build time.

-- 
Josh