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

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Date:   Sat, 6 May 2017 16:24:47 +0200 (CEST)
From:   Jiri Kosina <jikos@...nel.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
cc:     Jiri Slaby <jslaby@...e.cz>,
        Andrew Morton <akpm@...ux-foundation.org>,
        live-patching@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        the arch/x86 maintainers <x86@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>
Subject: Re: [PATCH 7/7] DWARF: add the config option


[ adding Josh to CC ]

On Fri, 5 May 2017, Linus Torvalds wrote:

> > The DWARF unwinder is in place and ready. So introduce the config option
> > to allow users to enable it. It is by default off due to missing
> > assembly annotations.
> 
> Who actually ends up using this?

As a datapoint -- we've been using dwarf unwinder in SUSE kernels since 
stone age, because we do not enable frame pointer, as it adds up to 10% of 
runtime slowdown for certain workloads, but we want reliable stacktraces 
so that we can actually debug user reports.

Now that we have nicely reliable stacktraces thanks to Josh's objtool for 
FP-enabled builds, we'd like to bring comparably understandable traces 
also to non-FP enabled builds.

> Put another way; the last time we did crazy stuff like this, it got
> reverted. For a damn good reason, despite some people being in denial
> about those reasons.

There had been personal issues involved previously, no questions about 
that :)

Thanks,

-- 
Jiri Kosina
SUSE Labs