Re: [PATCH] Rename is_compat_task to in_compat_syscall

[Andy Lutomirski <luto@amacapital.net>]

On Tue, Jan 19, 2016 at 2:16 PM, David Miller <davem@davemloft.net> wrote:
> From: Al Viro <viro@ZenIV.linux.org.uk>
> Date: Tue, 19 Jan 2016 21:55:36 +0000
>
>> On Tue, Jan 19, 2016 at 01:47:24PM -0800, Andy Lutomirski wrote:
>>> Essentially all users of is_compat_task in the kernel are trying to
>>> determine whether they are executing in the context of a compat
>>> syscall.  On at least x86_64 and sparc, these are not at all the
>>> same question.
>>>
>>> On x86_64 and sparc, therefore, is_compat_task doesn't return the
>>> overall compat state of the task; it returns true if the task is
>>> currently in a compat syscall.
>>
>> The hell it does.  Andy, TIF_32BIT is *NOT* set on syscall entry; it is
>> set by execve().  And 64bit task (with that bit clear) can bloody well
>> issue 32bit syscalls.  Really.
>
> Correct.

See the other thread.  My patch here is garbage, but x86 and sparc
really do work differently here, and I think that x86's behavior is
better than sparc's.

-- 
Andy Lutomirski
AMA Capital Management, LLC