linux-kernel - Re: X32 project status update

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Message-ID: <BANLkTi=ZXJzALg8tka21vvzYeeMajGuXHw@mail.gmail.com>
Date:	Sat, 21 May 2011 12:39:06 -0700
From:	"H.J. Lu" <hjl.tools@...il.com>
To:	"H. Peter Anvin" <h.peter.anvin@...el.com>
Cc:	x32-abi@...glegroups.com, Arnd Bergmann <arnd@...db.de>,
	GCC Development <gcc@....gnu.org>,
	GNU C Library <libc-alpha@...rceware.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: X32 project status update

On Sat, May 21, 2011 at 11:55 AM, H. Peter Anvin
<h.peter.anvin@...el.com> wrote:
> On 05/21/2011 09:27 AM, H.J. Lu wrote:
>> On Sat, May 21, 2011 at 8:34 AM, H.J. Lu <hjl.tools@...il.com> wrote:
>>> On Sat, May 21, 2011 at 8:27 AM, Arnd Bergmann <arnd@...db.de> wrote:
>>>> On Saturday 21 May 2011 17:01:33 H.J. Lu wrote:
>>>>> This is the x32 project status update:
>>>>>
>>>>> https://sites.google.com/site/x32abi/
>>>>>
>>>>
>>>> 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
    calls.
    5. Generate unistd_x32.h from unistd_64.h, replacing __NR_x32_ with
    _NR_.
    6. Install user-space unistd_64.h, replacing __NR_64_ with _NR_.

-- 
H.J.

View attachment "linux-x32-merge-1.patch" of type "text/plain" (101896 bytes)