From: Nick Desaulniers <ndesaulniers@google.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)"
<x86@kernel.org>, Peter Oberparleiter <oberpar@linux.ibm.com>,
LKML <linux-kernel@vger.kernel.org>,
Johannes Berg <johannes.berg@intel.com>,
Nathan Chancellor <nathan@kernel.org>,
Kees Cook <keescook@chromium.org>, Marco Elver <elver@google.com>,
Mark Rutland <mark.rutland@arm.com>
Subject: Re: [PATCH] gcov,x86: Mark GCOV broken for x86
Date: Mon, 14 Jun 2021 11:05:35 -0700 [thread overview]
Message-ID: <CAKwvOdmPTi93n2L0_yQkrzLdmpxzrOR7zggSzonyaw2PGshApw@mail.gmail.com> (raw)
In-Reply-To: <20210614162018.GD68749@worktop.programming.kicks-ass.net>
On Mon, Jun 14, 2021 at 9:20 AM Peter Zijlstra <peterz@infradead.org> wrote:
>
> On Mon, Jun 14, 2021 at 09:05:04AM -0700, Nick Desaulniers wrote:
> > On Mon, Jun 14, 2021 at 3:17 AM Peter Zijlstra <peterz@infradead.org> wrote:
> > >
> > >
> > > As recently discovered, there is no function attribute to disable the
> > > -fprofile-generate instrumentation. As such, GCOV is fundamentally
> > > incompatible with architectures that rely on 'noinstr' for correctness.
> >
> > Is there context for comment, or is this patch meant as a joke?
>
> Only if you think recursion in exception entry code is funny.
>
> noinstr *MUST* disable any and all compiler generated instrumentation,
> currently it that isn't the case for -fprofile-gnerate, nor
> -fprofile-arc.
>
> Look for all the fun we had with KCOV back then. Luckily KCOV
> instrumentation was trivial to patch out using objtool, so that's what
> x86 is currently doing.
>
> Luckily both compilers grew a __no_sanitize_coverage recently and we no
> longer have to rely on objtool fixing up the compiler output for much
> longer.
>
> https://lkml.kernel.org/r/20210527194448.3470080-1-elver@google.com
>
> Now all we need is one more such attribute to kill -fprofile-* stuff.
__attribute__((no_instrument_function)) is already wired to not emit
calls to mcount()/fentry(). I think extending it to also apply to
coverage (-fprofile-arcs) and instrumentation based profiling
(-fprofile-generate) is reasonable.
--
Thanks,
~Nick Desaulniers
next prev parent reply other threads:[~2021-06-14 18:06 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-14 10:17 [PATCH] gcov,x86: Mark GCOV broken for x86 Peter Zijlstra
2021-06-14 10:31 ` Marco Elver
2021-06-14 14:43 ` Peter Oberparleiter
2021-06-18 11:13 ` Peter Zijlstra
2021-06-21 13:53 ` Peter Oberparleiter
2021-06-14 16:05 ` Nick Desaulniers
2021-06-14 16:20 ` Peter Zijlstra
2021-06-14 18:05 ` Nick Desaulniers [this message]
2021-06-14 18:20 ` Borislav Petkov
2021-06-14 19:03 ` Nick Desaulniers
2021-06-14 19:28 ` Borislav Petkov
2021-06-14 18:31 ` Fangrui Song
2021-06-14 19:07 ` Peter Zijlstra
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=CAKwvOdmPTi93n2L0_yQkrzLdmpxzrOR7zggSzonyaw2PGshApw@mail.gmail.com \
--to=ndesaulniers@google.com \
--cc=elver@google.com \
--cc=johannes.berg@intel.com \
--cc=keescook@chromium.org \
--cc=linux-kernel@vger.kernel.org \
--cc=mark.rutland@arm.com \
--cc=nathan@kernel.org \
--cc=oberpar@linux.ibm.com \
--cc=peterz@infradead.org \
--cc=x86@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).