Re: How should nano_sleep be fixed (was: ptrace(), fork(), sleep(), exit(), SIGCHLD)

[Russell King <rmk@arm.linux.org.uk>]

On Thu, Aug 16, 2001 at 06:00:10PM +0200, christophe barbé wrote:
> Le jeu, 16 aoû 2001 12:29:05, Russell King a écrit :
> > Note also that this is bogus as an architecture invariant.
> > 
> > On ARM, we have to pass a pt_regs pointer into any function that requires
> > it.
> 
> I'm not sure to understand your point.

Its quite simple:

int sys_foo(struct pt_regs regs)
{
}

does not reveal the user space registers on ARM.  It instead reveals crap.
Why?  The ARM procedure call standard specifies that the first 4 words
of "regs" in this case are in 4 processor registers.  The other words
are on the stack immediately above the frame created by foo.  This is
not how the stack is layed out on ARM on entry to a sys_* function
due to the requirement for these to be restartable.

Instead, we must pass a pointer thusly:

int sys_foo(struct pt_regs *regs)
{
}

and the pointer is specifically setup and passed in by a very small
assembler wrapper.

> The first sentence tell me that the "struct pt_regs ..." line is x86
> specific and this was the reason behind my proposition to not add a _signal
> macro but a  _sys_nanosleep macro to include this too.

Correct.  But the act of getting "struct pt_regs" on entry to the function
is also architecture specific.

> The second sentence seem's to indicate that this is a classic problem for
> the ARM port. So if this is correct what is the best way to solve it ?

It used to be with such functions as sys_execve.  Then, sys_execve
became an architecture specific wrapper around do_execve (not by my
hand), so I guess that its not an ARM specific problem.

--
Russell King (rmk@arm.linux.org.uk)                The developer of ARM Linux
             http://www.arm.linux.org.uk/personal/aboutme.html