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SubjectRe: 32 bit user space compatibility
Hi,

Le mardi 28 octobre 2014 à 22:34 +0000, One Thousand Gnomes a écrit :
> On Sun, 26 Oct 2014 12:25:08 +0000
> "Skidanov, Alexey" <Alexey.Skidanov@amd.com> wrote:

>
> > Running 32 bit user space needs some work to be done with ioctls. I understand that there are two options to implement:
> > 1. Use only fixed size types. Pad IOCTLS params to multiple of 64 bits - simple; don't know if it covers all compatibility issues;
> > 2. 32 bit compatibility layer (through compat_ioctl, just like many drivers in kernel implement) - just a little bit simple code with some translations; really covers all issues;
> >
> > Which one is preferred by kernel community?
>
> You shouldn't need to pad paramters in most cases as platform alignment
> rules are usually sane for 32 and 64bit.

In most case, except i386 (ia32) vs amd64 (x86_64): u64 are going to be
aligned on 4 bytes boundaries for 32bits ABI and 8 bytes boundaries for
64bits ABI.

I've tried to explained this issue in a lightning talk[1][2] I'd given
at Kernel Recipes[3] this year.

[1] http://opteya.com/talks/2014/kernel-recipes/lightning-talk-kernel-userspace-ABI/
[2] https://gitorious.org/opteya/talk-kernel-userspace-abi
[3] http://kernel.recipes/

Regards.

--
Yann Droneaud
OPTEYA



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