linux-kernel - Re: X32 project status update

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Message-ID: <BANLkTikGQ-enRmWOFRGw-yJ=omeQZCrppw@mail.gmail.com>
Date:	Sat, 21 May 2011 16:48:36 -0700
From:	"H.J. Lu" <hjl.tools@...il.com>
To:	"Anvin, H Peter" <h.peter.anvin@...el.com>
Cc:	"x32-abi@...glegroups.com" <x32-abi@...glegroups.com>,
	"arnd@...db.de" <arnd@...db.de>,
	"gcc@....gnu.org" <gcc@....gnu.org>,
	"libc-alpha@...rceware.org" <libc-alpha@...rceware.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: X32 project status update

On Sat, May 21, 2011 at 1:01 PM, Anvin, H Peter <h.peter.anvin@...el.com> wrote:
> I'll look at it but possibly not until the weekend.

I checked it into hjl/x32/syscall branch at

http://git.kernel.org/?p=linux/kernel/git/hjl/linux-2.6.38.y.git;a=summary


H.J.
---
> -----Original Message-----
> From: H.J. Lu [hjl.tools@...il.com]
> Sent: Saturday, May 21, 2011 12:39 PM Pacific Standard Time
> To: Anvin, H Peter
> Cc: x32-abi@...glegroups.com; 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@...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.
>



-- 
H.J.
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