Re: Architectures where unaligned access is (not) OK?
On Mon, Nov 24, 2014 at 10:38 AM, Riku Voipio <riku.voipio@iki.fi> wrote:
> On Sat, Nov 22, 2014 at 11:03:16PM +0100, Bastien ROUCARIES wrote:
>> On Sat, Nov 22, 2014 at 10:37 PM, brian m. carlson
>> <sandals@crustytoothpaste.net> wrote:
>> > On Sat, Nov 22, 2014 at 09:42:43PM +0100, Jakub Wilk wrote:
>> >> * Henrique de Moraes Holschuh <hmh@debian.org>, 2014-11-21, 17:34:
>> >> >i386:
>> >> > __asm__("pushf\norl $0x40000,(%esp)\npopf");
>> >>
>> >> It works! Actually, it works so well it makes puts("hello world") die with
>> >> SIGBUS. :-(
>> >
>> > Yeah, that's my experience, too. glibc is not alignment check-safe on
>> > i386 and amd64. If you turn it on in an LD_PRELOAD using _init, it
>> > segfaults before main.
>
>> I have improved https://wiki.debian.org/ArchitectureSpecificsMemo fell
>> free to add to it.
>
> Thanks for updates. However, I'm not sure if the current unaligned
> accesses letters make it clear:
>
> Y=Yes, O=Often generally ok but ma fail in some specific case, T=Traps
> may be fixed by kernel (super slow),M=Maybe generally not ok, N=No raise
> SIGBUS. See detail below
i am open to suggestion
> Now, the M/T for armel/armhf/arm64 which is ambigous and misleading.
> Better make if clear:
>
> armel: no
No = sigbus ? or trap ?
> armhf: yes (exceptions as listed by Leif)
So it is often like i386
> arm64: yes (exceptions as listed by Leif)
often
>
> And then link to Leif's mail rather than copy the text unattributed on
> already long wikipage.
OK will add link. But I think the page will grow with fpu stuff...
> Riku
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