From: Peter Zijlstra <peterz@infradead.org>
To: Ard Biesheuvel <ardb@kernel.org>
Cc: linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org,
Josh Poimboeuf <jpoimboe@redhat.com>,
Jason Baron <jbaron@akamai.com>,
Steven Rostedt <rostedt@goodmis.org>,
Mark Rutland <mark.rutland@arm.com>,
Kees Cook <keescook@chromium.org>
Subject: Re: [RFC PATCH 1/7] static_call: get rid of static_call_cond()
Date: Tue, 9 Nov 2021 19:38:20 +0100 [thread overview]
Message-ID: <YYrAHMy8xmPXj4ql@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20211109164549.1724710-2-ardb@kernel.org>
On Tue, Nov 09, 2021 at 05:45:43PM +0100, Ard Biesheuvel wrote:
> The main reason for the existence of static_call_cond() seems to be that
> in theory, when using the generic implementation of static calls, it may
> be possible for a compiler to elide the indirect call entirely if the
> target is NULL, while still guaranteeing that all side effects of
> argument evaluation occur as expected.
>
> This is rather optimistic: as documented by an existing code comment,
> both GCC and Clang (version 10) get this wrong, and even if they ever
> get it right, this is far too subtle to rely on for a code path that is
> expected to be used only by the 'remaining' architectures once all the
> best supported ones implement either the out-of-line or inline optimized
> variety of static calls.
>
> Given that having static_call_cond() clutters up the API, and puts the
> burden on the caller to go and check what kind of static call they are
> dealing with, let's just get rid of the distinction.
No, static_call_cond() signifies the function can be NULL. Both gcc and
clang generate correct (but wildly ineffecient) code for this. Without
static_call_cond() the generic implementation will do a NULL deref.
That is, static_call_cond() does properly encapuslate:
func = READ_ONCE(key.func);
if (func)
func(ARGS);
You can't take that out.
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2021-11-09 18:40 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-09 16:45 [RFC PATCH 0/7] static call updates Ard Biesheuvel
2021-11-09 16:45 ` [RFC PATCH 1/7] static_call: get rid of static_call_cond() Ard Biesheuvel
2021-11-09 18:38 ` Peter Zijlstra [this message]
2021-11-09 18:41 ` Ard Biesheuvel
2021-11-09 19:22 ` Peter Zijlstra
2021-11-09 19:32 ` Peter Zijlstra
2021-11-09 16:45 ` [RFC PATCH 2/7] static_call: deal with unexported keys without cluttering up the API Ard Biesheuvel
2021-11-09 18:49 ` Peter Zijlstra
2021-11-09 18:53 ` Ard Biesheuvel
2021-11-09 19:41 ` Peter Zijlstra
2021-11-09 16:45 ` [RFC PATCH 3/7] static_call: use helper to access non-exported key Ard Biesheuvel
2021-11-09 18:53 ` Peter Zijlstra
2021-11-09 18:54 ` Ard Biesheuvel
2021-11-09 19:42 ` Peter Zijlstra
2021-11-09 19:45 ` Ard Biesheuvel
2021-11-09 16:45 ` [RFC PATCH 4/7] static_call: fix broken static_call_query() for non-exported keys Ard Biesheuvel
2021-11-09 18:56 ` Peter Zijlstra
2021-11-09 16:45 ` [RFC PATCH 5/7] static_call: use non-function types to refer to the trampolines Ard Biesheuvel
2021-11-09 16:45 ` [RFC PATCH 6/7] static_call: rename EXPORT_ macros to be more self-explanatory Ard Biesheuvel
2021-11-09 19:00 ` Peter Zijlstra
2021-11-09 19:03 ` Ard Biesheuvel
2021-11-09 16:45 ` [RFC PATCH 7/7] static_call: add generic support for non-exported keys Ard Biesheuvel
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=YYrAHMy8xmPXj4ql@hirez.programming.kicks-ass.net \
--to=peterz@infradead.org \
--cc=ardb@kernel.org \
--cc=jbaron@akamai.com \
--cc=jpoimboe@redhat.com \
--cc=keescook@chromium.org \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=mark.rutland@arm.com \
--cc=rostedt@goodmis.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