RE: X32 project status update

From: Anvin, H Peter
Date: Sat May 21 2011 - 16:02:00 EST

I'll look at it but possibly not until the weekend.

-----Original Message-----
From: H.J. Lu [<>]
Sent: Saturday, May 21, 2011 12:39 PM Pacific Standard Time
To: Anvin, H Peter
Cc: x32-abi@xxxxxxxxxxxxxxxx; Arnd Bergmann; GCC Development; GNU C Library; LKML
Subject: Re: X32 project status update

On Sat, May 21, 2011 at 11:55 AM, H. Peter Anvin
<h.peter.anvin@xxxxxxxxx> wrote:
> On 05/21/2011 09:27 AM, H.J. Lu wrote:
>> On Sat, May 21, 2011 at 8:34 AM, H.J. Lu <> wrote:
>>> On Sat, May 21, 2011 at 8:27 AM, Arnd Bergmann <arnd@xxxxxxxx> wrote:
>>>> On Saturday 21 May 2011 17:01:33 H.J. Lu wrote:
>>>>> This is the x32 project status update:
>>>> I've had another look at the kernel patch. It basically
>>>> looks all good, but the system call table appears to
>>>> diverge from the x86_64 list for no (documented) reason,
>>>> in the calls above 302. Is that intentional?
>>>> I can see why you might want to keep the numbers identical,
>>>> but if they are already different, why not use the generic
>>>> system call table from asm-generic/unistd.h for the new
>>>> ABI?
>>> We can sort it out when we start merging x32 kernel changes.
>> Peter, is that possible to use the single syscall table for
>> both x86-64 and x32 system calls? Out of 300+ system
>> calls, only 84 are different for x86-64 and x32. That
>> is additional 8*84 == 672 bytes in syscall table.
> Sort of... remember we talked about merging system calls at the tail
> end? The problem with that is that some system calls (like read()!)
> actually are different system calls in very subtle situations, due to
> abuse in some subsystems of the is_compat() construct. I think that may
> mean we have to have an unambiguous flag after all...
> Now, perhaps we can use a high bit for that and mask it before dispatch,
> then we don't need the additional table. A bit of a hack, but it should
> work.

How about this patch?

Merge x32 system calls with x86-64 system calls

Implemented with

1. Mark all x86-64 specific system calls with __NR_64_.
2. Mark all x32 specific system calls with __NR_x32_.
3. Include unistd_64_compat.h, instead of unistd_x32.h for kernel
build, which provides __NR_ versions of x86-64 specific system calls.
4. Append x32 specific system calls after the current x86-64 system
5. Generate unistd_x32.h from unistd_64.h, replacing __NR_x32_ with
6. Install user-space unistd_64.h, replacing __NR_64_ with _NR_.

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