linux-kernel - Re: [PATCH] drm/virtio: use %llu format string form atomic64

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAMuHMdWbzEFqVctMXTWtdBn2B+guFdphQX5nXUnHPo1szQbtPg@mail.gmail.com>
Date:	Mon, 19 Oct 2015 09:34:15 +0200
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Linux MIPS Mailing List <linux-mips@...ux-mips.org>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	DRI Development <dri-devel@...ts.freedesktop.org>,
	virtualization@...ts.linux-foundation.org,
	Gerd Hoffmann <kraxel@...hat.com>,
	Dave Airlie <airlied@...hat.com>,
	Ralf Baechle <ralf@...ux-mips.org>
Subject: Re: [PATCH] drm/virtio: use %llu format string form atomic64_t

On Wed, Oct 7, 2015 at 1:23 PM, Arnd Bergmann <arnd@...db.de> wrote:
> On Wednesday 07 October 2015 13:04:06 Arnd Bergmann wrote:
>> On Wednesday 07 October 2015 11:45:02 Russell King - ARM Linux wrote:
>> > On Wed, Oct 07, 2015 at 12:41:21PM +0200, Arnd Bergmann wrote:
>> > > The virtgpu driver prints the last_seq variable using the %ld or
>> > > %lu format string, which does not work correctly on all architectures
>> > > and causes this compiler warning on ARM:
>> > >
>> > > drivers/gpu/drm/virtio/virtgpu_fence.c: In function 'virtio_timeline_value_str':
>> > > drivers/gpu/drm/virtio/virtgpu_fence.c:64:22: warning: format '%lu' expects argument of type 'long unsigned int', but argument 4 has type 'long long int' [-Wformat=]
>> > >   snprintf(str, size, "%lu", atomic64_read(&fence->drv->last_seq));
>> > >                       ^
>> > > drivers/gpu/drm/virtio/virtgpu_debugfs.c: In function 'virtio_gpu_debugfs_irq_info':
>> > > drivers/gpu/drm/virtio/virtgpu_debugfs.c:37:16: warning: format '%ld' expects argument of type 'long int', but argument 3 has type 'long long int' [-Wformat=]
>> > >   seq_printf(m, "fence %ld %lld\n",
>> > >                 ^
>> > >
>> > > In order to avoid the warnings, this changes the format strings to %llu
>> > > and adds a cast to u64, which makes it work the same way everywhere.
>> >
>> > You have to wonder why atomic64_* functions do not use u64 types.
>> > If they're not reliant on manipulating 64-bit quantities, then what's
>> > the point of calling them atomic _64_.
>>
>> I haven't checked all architectures, but I assume what happens is that
>> 64-bit ones just #define atomic64_t atomic_long_t, so they don't have
>> to provide three sets of functions.
>
> scratch that, I just looked at all the architectures and found that it's
> just completely arbitrary, even within one architecture you get a mix
> of 'long' and 'long long', plus this gem from MIPS:
>
> static __inline__ int atomic64_add_unless(atomic64_t *v, long a, long u)
>
> which truncates the result to 32 bit.

Woops.

See also my unanswered question in "atomic64 on 32-bit vs 64-bit (was:
Re: Add virtio gpu driver.)", which is still valid:
https://lkml.org/lkml/2015/6/28/18

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/