From: Daniel Axtens <dja@axtens.net>
To: keescook@chromium.org
Cc: catalin.marinas@arm.com, clang-built-linux@googlegroups.com,
hca@linux.ibm.com, jarmo.tiitto@gmail.com,
linux-kernel@vger.kernel.org, lukas.bulwahn@gmail.com,
mark.rutland@arm.com, masahiroy@kernel.org, maskray@google.com,
morbo@google.com, nathan@kernel.org, ndesaulniers@google.com,
oberpar@linux.ibm.com, ojeda@kernel.org, peterz@infradead.org,
samitolvanen@google.com, torvalds@linux-foundation.org,
wcw@google.com, will@kernel.org
Subject: Re: ARCH_WANTS_NO_INSTR (Re: [GIT PULL] Clang feature updates for v5.14-rc1)
Date: Wed, 06 Oct 2021 00:45:45 +1100 [thread overview]
Message-ID: <874k9v60vq.fsf@dja-thinkpad.axtens.net> (raw)
In-Reply-To: <20211005131015.3153458-1-dja@axtens.net>
> Kconfig: Introduce ARCH_WANTS_NO_INSTR and CC_HAS_NO_PROFILE_FN_ATTR
>
> We don't want compiler instrumentation to touch noinstr functions,
> which are annotated with the no_profile_instrument_function function
> attribute. Add a Kconfig test for this and make GCOV depend on it, and
> in the future, PGO.
>
> If an architecture is using noinstr, it should denote that via this
> Kconfig value. That makes Kconfigs that depend on noinstr able to express
> dependencies in an architecturally agnostic way.
>
> However, things in generic code (such as rcu_nmi_enter) are tagged with
> `noinstr`, so I'm worried that this commit subtly breaks things like KASAN on
> platforms that haven't opted in yet. (I stumbled across this while developing
> KASAN on ppc64, but at least riscv and ppc32 have KASAN but not
> ARCH_WANTS_NO_INSTR already.)
Hmm, so it looks like the commit doesn't affect how noinstr is compiled
(which means I have another different issue to contend with!), but...
> As I said, I haven't been able to find the original thread - is there any reason
> this shouldn't be always on? Why would an arch not opt in? What's the motivation
> for ignoring the noinstr markings?
>
> Should generic KASAN/KCSAN/anything else marked in noinstr also have markings
> requring ARCH_WANTS_NO_INSTR? AFAICT they should, right?
I'm still curious about all of these questions. I get
CC_HAS_NO_PROFILE_FN_ATTR, but I don't get ARCH_WANTS_NO_INSTR.
Kind regards,
Daniel
>
> Kind regards,
> Daniel
next prev parent reply other threads:[~2021-10-05 13:45 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-28 19:32 [GIT PULL] Clang feature updates for v5.14-rc1 Kees Cook
2021-06-29 2:49 ` Linus Torvalds
2021-06-29 20:44 ` Kees Cook
2021-06-29 21:03 ` Linus Torvalds
2021-06-29 21:27 ` Nick Desaulniers
2021-06-29 21:57 ` Linus Torvalds
2021-07-07 8:10 ` Ingo Molnar
2021-07-02 12:46 ` Bill Wendling
2021-07-02 12:56 ` Peter Zijlstra
2021-07-02 17:26 ` Nick Desaulniers
2021-07-02 18:57 ` Peter Zijlstra
2021-07-02 19:53 ` Nick Desaulniers
2022-10-31 23:55 ` Bill Wendling
2021-06-29 13:14 ` Mark Rutland
2021-06-29 20:11 ` Kees Cook
2021-06-29 21:05 ` Nick Desaulniers
2021-10-05 13:10 ` ARCH_WANTS_NO_INSTR (Re: [GIT PULL] Clang feature updates for v5.14-rc1) Daniel Axtens
2021-10-05 13:45 ` Daniel Axtens [this message]
2021-10-05 14:30 ` Mark Rutland
2021-10-07 6:19 ` Jarmo Tiitto
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