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SubjectRe: How should nano_sleep be fixed (was: ptrace(), fork(), sleep(), exit(), SIGCHLD)
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 ( The developer of ARM Linux

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