From: David Laight <David.Laight@ACULAB.COM>
To: 'Joe Perches' <joe@perches.com>, LKML <linux-kernel@vger.kernel.org>
Cc: kernel-janitors <kernel-janitors@vger.kernel.org>
Subject: RE: Use of '%#02x' is almost always wrong
Date: Tue, 12 Oct 2021 21:10:32 +0000 [thread overview]
Message-ID: <f41e216ed5074c55ad024e68a7dfaa3c@AcuMS.aculab.com> (raw)
In-Reply-To: <b04a10ea9682c51764053c1be73d4b3be59d1e7f.camel@perches.com>
From: Joe Perches
> Sent: 10 October 2021 17:46
>
> Perhaps too many developers do not know that using '%#<width>x'
> in printf output _includes_ the 0x prefix in the output width.
>
> So %#02x already has the width taken by the 0x prefix and will
> always emit 3 or more output bytes.
>
> sprintf(buf, "%#02x", 1) emits 0x1 (3 bytes of output)
> sprintf(buf, "%#02x", 255) emits 0xff (4 bytes of output)
>
> So presumably all the uses of %#02x in the kernel are not outputting
> what is actually expected. Perhaps all of these should use %#04x.
Doesn't help. The definition of "%#x" is completely broken.
Basically 0 doesn't get the "0x" prefix, so "%#04x" outputs
"0000" if the value is zero.
So the correct replacement is (probably) "0x%02x".
David
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Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
next prev parent reply other threads:[~2021-10-12 21:10 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-10 16:45 Use of '%#02x' is almost always wrong Joe Perches
2021-10-12 21:10 ` David Laight [this message]
2021-10-13 23:16 ` Bernd Petrovitsch
2021-10-14 8:27 ` David Laight
2021-10-13 6:15 ` Dan Carpenter
2021-10-13 8:17 ` Joe Perches
2021-10-13 10:39 ` Dan Carpenter
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