Re: [PATCH] fix trap in parallel for m32r-sim

Doug Evans
2004-01-19T23:05:40Z

Kazuhiro Inaoka writes:
> Hi Doug,
>
> I want to fix the following problem.
>
> test pattern is:
> main()
> {
> asm("trap #0 || ldi r0,#1"); /* the same as exit() ? */
>
> abort();
> }

Ah hah! So this is about TRAP_SYSCALL. :-)
TRAP_SYSCALL is a simulator-only facility to simplify printf,exit,etc.

I gather you want r0 to be 1 before the trap is taken,
violating standard parallel execution semantics: all inputs
read before any outputs written.
i.e. you want the trap to _read_ the value of r0 and get 1.
This is different than the violation I refered to previously
where the trap will _write_ the value of r0, say, before
other insns have read their inputs.

It seems like you're trying to fix a broken program by breaking
(or at least hacking) the simulator. How about instead just having
a rule that says the TRAP_SYSCALL trap cannot be paired with instructions
that set up inputs for the syscall? This would be no different
than trying to make

asm ("add r1,r0 || ldi r0,#1"); // increment r1 by 1

work. It doesn't work because the `add' will read the value of r0
before the ldi has set it to 1.
[apologies if I got the syntax wrong, haven't programmed m32r
assembler in a while :-)]

> command line:
> m32r-elf-gcc -m32rx test.c
>
> In this case, it will pass through an asm function without exit.
> At the time of m32r_trap() execution, r0 is not 1 yet.
> It's not a problem of the current simulator implementation for trap
> instruction.
> I think it's a problem of timing to call back system call when trap is in
> parallel.
>
> Changed a patch and comment.
>
> Regards,
>
> Kazuhiro Inaoka
>
> sim/m32r/ChangeLog
>
> 2004-01-19 Kazuhiro Inaoka < inaoka dot kazuhiro at renesas dot com >
>
> * mloopx.in (xextract-pbb): Fixed trap for system calls operation
> in parallel.
> * mloop2.in (xextract-pbb): Ditto.