linux-kernel - Re: [PATCH] broken TASK_SIZE for ia32

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Date:	Sun, 6 May 2012 19:46:42 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Ralf Baechle <ralf@...ux-mips.org>
Subject: Re: [PATCH] broken TASK_SIZE for ia32_aout

On Sun, May 06, 2012 at 10:58:49AM -0700, H. Peter Anvin wrote:

> > What kind of semantics do we want?  "Thread property" one, set when we
> > set personality on execve(), or "syscall property", like e.g. x86 TIF_IRET
> > and TS_COMPAT?
> 
> It depends on the ABI properties of the platform.  The x86 compat ABI is
> that any task can issue a compat ABI request and get a compat ABI
> response (a 64-bit task can call int $0x80 for an ia32 syscall
> invocation, or use syscall with either an x86-64 or and x32 system call
> number.)  So is_compat_task() returns the current system call mode of
> the task, because that is what downstream users need.  One of the
> biggest users is the input subsystem, which earns the black mark for
> worst possible ABI design, and that definitely depends on the system
> call type being invoked.

Umm...  Let me restate that question: is there ever a case when it would
_not_ be a syscall property?  I.e. when both 64bit and 32bit syscalls are
possible for a given process *and* callers of is_compat_task() care about
the kind of process and not the kind of syscall?

Is e.g. sparc behaviour ("what kind of process it is, regardless of whether
we are issuing a 32bit or a 64bit syscall") correct?

Sure, on a platform where the possible kind of syscall is a function of
process' personality, a thread property can be a used to tell which
kind of syscall we are in.
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