From: "Jason A. Donenfeld" <Jason@zx2c4.com>
To: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
linux-kernel@vger.kernel.org, linux-kbuild@vger.kernel.org,
linux-arch@vger.kernel.org, linux-toolchains@vger.kernel.org,
Masahiro Yamada <masahiroy@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
ndesaulniers@google.com
Subject: Re: [PATCH v2] kbuild: treat char as always unsigned
Date: Thu, 20 Oct 2022 21:01:32 -0400 [thread overview]
Message-ID: <Y1HvbO6wnhoHrszN@zx2c4.com> (raw)
In-Reply-To: <202210201056.DEE610F6F@keescook>
On Thu, Oct 20, 2022 at 11:41:29AM -0700, Kees Cook wrote:
> On Wed, Oct 19, 2022 at 05:38:55PM -0700, Linus Torvalds wrote:
> > Having some scripting automation that just notices "this changes code
> > generation in function X" might actually be interesting, and judging
> > by my quick tests might not be *too* verbose.
>
> On the reproducible build comparison system[1] we use for checking a lot
> of the KSPP work for .text deltas, an allmodconfig finds a fair bit for
> this change. Out of 33900 .o files, 1005 have changes.
>
> Spot checking matches a lot of what you found already...
>
> u64 flags = how->flags;
> ...
> fs/open.c:1123:
> int acc_mode = ACC_MODE(flags);
> - 1c86: movsbl 0x0(%rdx),%edx
> + 1c86: movzbl 0x0(%rdx),%edx
>
> #define ACC_MODE(x) ("\004\002\006\006"[(x)&O_ACCMODE])
>
> Ignoring those, it goes down to 625, and spot checking those is more
> difficult, but looks to be mostly register selection changes dominating
> the delta. The resulting vmlinux sizes are identical, though.
>
> -Kees
>
> [1] A fancier version of:
> https://outflux.net/blog/archives/2022/06/24/finding-binary-differences/
Say, don't we have some way of outputting LLVM IL? I saw some
-fno-discard-value-names floating through a few days ago. Apparently you
can do `make LLVM=1 fs/select.ll`? This might have less noise in it.
I'll play on the airplane tomorrow.
Jason
next prev parent reply other threads:[~2022-10-21 1:02 UTC|newest]
Thread overview: 70+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-10-19 16:26 [PATCH] kbuild: treat char as always signed Jason A. Donenfeld
2022-10-19 16:54 ` Segher Boessenkool
2022-10-19 17:14 ` Linus Torvalds
2022-10-19 17:26 ` Linus Torvalds
2022-10-19 18:10 ` Nick Desaulniers
2022-10-19 18:35 ` Linus Torvalds
2022-10-19 19:23 ` Andy Shevchenko
2022-10-19 19:36 ` Linus Torvalds
2022-10-19 17:43 ` Segher Boessenkool
2022-10-19 18:11 ` Linus Torvalds
2022-10-19 18:20 ` Nick Desaulniers
2022-10-19 18:56 ` Linus Torvalds
2022-10-19 19:11 ` Kees Cook
2022-10-19 19:30 ` Linus Torvalds
2022-10-19 20:35 ` Jason A. Donenfeld
2022-10-20 0:10 ` Linus Torvalds
2022-10-20 3:11 ` Jason A. Donenfeld
2022-10-19 20:15 ` Segher Boessenkool
2022-10-19 21:07 ` David Laight
2022-10-19 21:26 ` Segher Boessenkool
2022-10-20 10:41 ` Gabriel Paubert
2022-10-21 22:46 ` Linus Torvalds
2022-10-22 6:06 ` Gabriel Paubert
2022-10-22 18:16 ` Linus Torvalds
2022-10-23 20:23 ` Gabriel Paubert
2022-10-25 23:00 ` Kees Cook
2022-10-26 0:04 ` Jason A. Donenfeld
2022-10-26 15:41 ` Kees Cook
2022-10-19 19:54 ` Linus Torvalds
2022-10-19 20:23 ` Jason A. Donenfeld
2022-10-19 20:30 ` [PATCH v2] kbuild: treat char as always unsigned Jason A. Donenfeld
2022-10-19 23:56 ` Linus Torvalds
2022-10-20 0:02 ` Jason A. Donenfeld
2022-10-20 0:38 ` Linus Torvalds
2022-10-20 2:59 ` Jason A. Donenfeld
2022-10-20 18:41 ` Kees Cook
2022-10-21 1:01 ` Jason A. Donenfeld [this message]
2022-10-20 20:24 ` Segher Boessenkool
2022-10-24 9:24 ` Dan Carpenter
2022-10-24 9:30 ` Dan Carpenter
2022-10-24 16:33 ` Jason A. Donenfeld
2022-10-24 17:10 ` Linus Torvalds
2022-10-24 17:17 ` Jason A. Donenfeld
2022-10-25 19:22 ` Kalle Valo
2022-10-25 10:16 ` David Laight
2022-10-24 15:17 ` Jason A. Donenfeld
2022-12-21 14:53 ` Guenter Roeck
2022-12-21 15:05 ` Geert Uytterhoeven
2022-12-21 15:23 ` Guenter Roeck
2022-12-21 15:29 ` Rasmus Villemoes
2022-12-21 15:56 ` Guenter Roeck
2022-12-21 17:06 ` Linus Torvalds
2022-12-21 17:19 ` Guenter Roeck
2022-12-21 18:46 ` Linus Torvalds
2022-12-21 19:08 ` Linus Torvalds
2022-12-21 21:01 ` Guenter Roeck
2022-12-22 13:05 ` Geert Uytterhoeven
2022-12-22 10:41 ` David Laight
[not found] ` <f02e0ac7f2d805020a7ba66803aaff3e31b5eeff.camel@t-online.de>
2022-12-24 9:47 ` Geert Uytterhoeven
2022-12-30 11:39 ` David Laight
2022-12-30 13:13 ` David Laight
2023-01-02 8:29 ` Geert Uytterhoeven
2022-12-21 17:49 ` Andreas Schwab
2022-12-21 16:57 ` Geert Uytterhoeven
2022-10-19 20:58 ` [PATCH] kbuild: treat char as always signed David Laight
2022-10-26 0:10 ` make ctype ascii only? (was [PATCH] kbuild: treat char as always signed) Rasmus Villemoes
2022-10-26 18:10 ` Linus Torvalds
2022-10-27 7:59 ` Rasmus Villemoes
2022-10-27 18:28 ` Linus Torvalds
[not found] ` <202210201618.8XhEGsLd-lkp@intel.com>
2022-10-20 16:33 ` [PATCH] kbuild: treat char as always signed Jason A. Donenfeld
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