From: Sascha Hauer <s.hauer@pengutronix.de>
To: Ahmad Fatoum <a.fatoum@pengutronix.de>
Cc: barebox@lists.infradead.org
Subject: Re: [PATCH 2/2] of: fix side effect in macro expansion
Date: Wed, 29 Apr 2020 10:41:47 +0200 [thread overview]
Message-ID: <20200429084147.GG5877@pengutronix.de> (raw)
In-Reply-To: <54196041-b8c0-6ba0-9122-19168a183e0d@pengutronix.de>
On Wed, Apr 29, 2020 at 10:26:27AM +0200, Ahmad Fatoum wrote:
> On 4/29/20 10:00 AM, Sascha Hauer wrote:
> > On Wed, Apr 29, 2020 at 08:40:40AM +0200, Ahmad Fatoum wrote:
> >> On little endian platforms that don't define __arch_swab32p, be32_to_cpu
> >> ultimately expands to an expression that evaluates its argument multiple
> >> times. Because of the increment, this is wrong (and UB because of
> >> unsequenced modification).
> >> Hoist the side effect out of the macro argument.
> >
> > I'm not sure if the reasoning is correct. That would mean that
> > of_read_number() doesn't work on ARM, but I can assure it actually does.
>
> Typo, sorry. arch needs to define __arch_swab32 (no p at the end).
>
> of_read_number -> be32_to_cpu -> __be32_to_cpu -> __swab32 -> __fswab32
>
> then
>
> static inline __attribute_const__ __u32 __fswab32(__u32 val)
> {
> #ifdef __arch_swab32
> return __arch_swab32(val);
> #else
> return ___constant_swab32(val);
> #endif
> }
>
> where ___constant_swab32 is the macro that evaluates the argument
> multiple times.
__fswab32 is a function, for the caller it doesn't matter how often
___constant_swab32 evaluates its argument.
Sascha
--
Pengutronix e.K. | |
Steuerwalder Str. 21 | http://www.pengutronix.de/ |
31137 Hildesheim, Germany | Phone: +49-5121-206917-0 |
Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |
_______________________________________________
barebox mailing list
barebox@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/barebox
next prev parent reply other threads:[~2020-04-29 8:41 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-29 6:40 [PATCH 1/2] scripts: imd: fix uninitialized variable read Ahmad Fatoum
2020-04-29 6:40 ` [PATCH 2/2] of: fix side effect in macro expansion Ahmad Fatoum
2020-04-29 8:00 ` Sascha Hauer
2020-04-29 8:26 ` Ahmad Fatoum
2020-04-29 8:41 ` Sascha Hauer [this message]
2020-04-29 8:47 ` Ahmad Fatoum
2020-04-29 7:38 ` [PATCH 1/2] scripts: imd: fix uninitialized variable read Sascha Hauer
2020-05-04 7:38 ` Steffen Trumtrar
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=20200429084147.GG5877@pengutronix.de \
--to=s.hauer@pengutronix.de \
--cc=a.fatoum@pengutronix.de \
--cc=barebox@lists.infradead.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