> this is fine for most calls, however rfork() explicitly sets up->nerrlab
> to zero rather than copying it and memmove()ing up->errlab from the parent
> proc to the child:
>
> /sys/src/9/port/sysproc.c:90
>
> Surely this means that rfork will always fail with a "bad errstack [19]: -1
> extra"
> error?
long
sysrfork(ulong *arg)
{
...
/* Craft a return frame which will cause the child to pop out of
* the scheduler in user mode with the return register zero
*/
forkchild(p, up->dbgreg);
...
ready(p);
...
}
void
forkchild(Proc *p, Ureg *ureg)
{
Ureg *cureg;
/*
* Add 2*BY2WD to the stack to account for
* - the return PC
* - trap's argument (ur)
*/
p->sched.sp = (ulong)p->kstack+KSTACK-(sizeof(Ureg)+2*BY2WD);
p->sched.pc = (ulong)forkret;
cureg = (Ureg*)(p->sched.sp+2*BY2WD);
memmove(cureg, ureg, sizeof(Ureg));
/* return value of syscall in child */
cureg->ax = 0;
/* Things from bottom of syscall which were never executed */
p->psstate = 0;
p->insyscall = 0;
}
TEXT forkret(SB), $0
POPL AX
POPAL
POPL GS
POPL FS
POPL ES
POPL DS
ADDL $8, SP /* pop error code and trap type */
IRETL
