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From: "Nicolai Hähnle" <nhaehnle@gmail.com>
To: Emil Velikov <emil.l.velikov@gmail.com>
Cc: "Nicolai Hähnle" <nicolai.haehnle@amd.com>,
	"ML dri-devel" <dri-devel@lists.freedesktop.org>
Subject: Re: [PATCH] xf86drm: ensure proper alignment of pointers in drmProcessPciDevice
Date: Tue, 17 May 2016 10:24:43 -0500	[thread overview]
Message-ID: <573B37BB.9030608@gmail.com> (raw)
In-Reply-To: <CACvgo50XNgQoxZAivvyAPwMP=zxyWcZ_Ha0c_Sg3LZ0ZQYdS1Q@mail.gmail.com>

Hi Emil,

On 14.05.2016 18:03, Emil Velikov wrote:
> Hi Nicolai,
>
> On 13 May 2016 at 07:14, Nicolai Hähnle <nhaehnle@gmail.com> wrote:
>> From: Nicolai Hähnle <nicolai.haehnle@amd.com>
>>
>> Previously, (*device)->businfo.pci would end up misaligned, which results
>> in undefined behavior.
>>
> Can you point me to a source where I can read more on the topic ?
> I'm pretty sure I ran this through valgrind and it gave a clear bill of health.

Valgrind doesn't complain here either, I noticed it with 
-fsanitize=undefined (ubsan) applied to Mesa.

That makes sense, since unaligned loads/stores aren't really a bug as 
far as the x86 ISA is concerned, which is the level at which valgrind 
looks at the code. On the other hand, apparently already an unaligned 
cast (not just the dereference!) is undefined behavior as far as C is 
concerned. I'm not a C language lawyer, but that's what people are 
saying on the interwebs, so it must be true :)

> P.S. Please run the following in your repo $git config --local
> format.subjectPrefix "PATCH libdrm"

Done.

Cheers,
Nicolai
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  reply	other threads:[~2016-05-17 15:24 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-05-13  6:14 [PATCH] xf86drm: ensure proper alignment of pointers in drmProcessPciDevice Nicolai Hähnle
2016-05-14 23:03 ` Emil Velikov
2016-05-17 15:24   ` Nicolai Hähnle [this message]
2016-06-10 14:07 ` Nicolai Hähnle
2016-06-10 16:55   ` Emil Velikov
2016-06-10 18:19     ` Nicolai Hähnle

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