From: Kees Cook <keescook@chromium.org>
To: "Jason A. Donenfeld" <Jason@zx2c4.com>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
linux-kernel@vger.kernel.org,
Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH v3 2/2] minmax: clamp more efficiently by avoiding extra comparison
Date: Mon, 26 Sep 2022 11:30:14 -0700 [thread overview]
Message-ID: <202209261127.0FBA8B7@keescook> (raw)
In-Reply-To: <20220926133435.1333846-2-Jason@zx2c4.com>
On Mon, Sep 26, 2022 at 03:34:35PM +0200, Jason A. Donenfeld wrote:
> [...]
> In this case, we actually gain a branch, unfortunately, because the
> compiler's replacement axioms no longer as cleanly apply.
>
> So all and all, this change is a bit of a mixed bag.
I'm on the fence -- I think the new macro is a more correct way to
describe the operation, though on the other hand, the old way provides a
simple way to compose the bounds checks.
I suspect we should probably optimize for _performance_, not code size,
so if the new branch is actually visible via cycle counts in "perf"
output, probably we shouldn't use this patch, and instead add a comment
about why it is defined the way it is.
-Kees
--
Kees Cook
next prev parent reply other threads:[~2022-09-26 18:30 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-23 10:06 [PATCH] minmax: clamp more efficiently by avoiding extra comparison Jason A. Donenfeld
2022-09-23 10:35 ` Andy Shevchenko
2022-09-23 10:40 ` Jason A. Donenfeld
2022-09-23 10:48 ` Jason A. Donenfeld
2022-09-23 15:12 ` Andy Shevchenko
2022-09-23 15:13 ` Jason A. Donenfeld
2022-09-23 15:40 ` [PATCH v2] " Jason A. Donenfeld
2022-09-23 16:41 ` Kees Cook
2022-09-23 16:42 ` Jason A. Donenfeld
2022-09-23 16:53 ` Andy Shevchenko
2022-09-23 16:54 ` Jason A. Donenfeld
2022-09-23 19:47 ` Kees Cook
2022-09-23 22:54 ` Andrew Morton
2022-09-24 0:02 ` Kees Cook
2022-09-24 10:37 ` Jason A. Donenfeld
2022-09-25 16:29 ` Andrew Morton
2022-09-26 10:00 ` Andy Shevchenko
2022-09-26 12:23 ` Jason A. Donenfeld
2022-09-26 13:34 ` [PATCH v3 1/2] minmax: sanity check constant bounds when clamping Jason A. Donenfeld
2022-09-26 13:34 ` [PATCH v3 2/2] minmax: clamp more efficiently by avoiding extra comparison Jason A. Donenfeld
2022-09-26 18:30 ` Kees Cook [this message]
2022-09-26 21:33 ` Jason A. Donenfeld
2022-09-26 13:46 ` [PATCH v3 1/2] minmax: sanity check constant bounds when clamping Andy Shevchenko
2022-09-26 18:26 ` Kees Cook
2022-10-04 13:41 ` Jason A. Donenfeld
2022-10-04 14:39 ` Kees Cook
2022-10-04 15:01 ` Jason A. Donenfeld
2022-09-26 18:30 ` [PATCH v2] minmax: clamp more efficiently by avoiding extra comparison Kees Cook
2022-09-23 15:10 ` [PATCH] " Andy Shevchenko
2022-09-23 15:11 ` Jason A. Donenfeld
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