> > A lot of this points towards a register window error in__tfork() which
> > affects only the parent process.
>
> I think the issue is that cpu_fork() copies the u_pcb from parent to child
> and with that the special user register windows that got spilled because
> of some TL>0 fault. Since __tfork() uses a new stack it makes no sense
> to keep those windows around and possibly fault them back from the new
> thread (onto the old stack).
That makes sense.
> The following diff seems to fix the above repoducer for me. Please test.
> I will need to add some comments etc there (also not sure if the bzero()
> calls are needed or if clearing pcb_nsaved is enough.
Actually, rather than bzero'ing pcb_rwsp and pcb_rw, it would be better
to only bcopy offsetof(struct pcb, pcb_rw) rather than sizeof(struct
pcb) on line 139, i.e. something like this:
Index: vm_machdep.c
===================================================================
RCS file: /OpenBSD/src/sys/arch/sparc64/sparc64/vm_machdep.c,v
retrieving revision 1.42
diff -u -p -r1.42 vm_machdep.c
--- vm_machdep.c 25 Oct 2022 06:05:57 -0000 1.42
+++ vm_machdep.c 15 Feb 2024 15:29:37 -0000
@@ -100,6 +100,7 @@ cpu_fork(struct proc *p1, struct proc *p
struct pcb *npcb = &p2->p_addr->u_pcb;
struct trapframe *tf2;
struct rwindow *rp;
+ size_t pcbsz;
extern struct proc proc0;
/*
@@ -136,7 +137,15 @@ cpu_fork(struct proc *p1, struct proc *p
#else
opcb->lastcall = NULL;
#endif
- bcopy((caddr_t)opcb, (caddr_t)npcb, sizeof(struct pcb));
+ /*
+ * If a new stack is provided, do not bother copying saved windows
+ * in the new pcb. Also, we'll reset pcb_nsaved accordingly below.
+ */
+ if (stack != NULL)
+ pcbsz = offsetof(struct pcb, pcb_rw);
+ else
+ pcbsz = sizeof(struct pcb);
+ bcopy((caddr_t)opcb, (caddr_t)npcb, pcbsz);
if (p1->p_md.md_fpstate) {
fpusave_proc(p1, 1);
p2->p_md.md_fpstate = malloc(sizeof(struct fpstate),
@@ -162,6 +171,7 @@ cpu_fork(struct proc *p1, struct proc *p
* with space reserved for the frame, and zero the frame pointer.
*/
if (stack != NULL) {
+ npcb->pcb_nsaved = 0;
tf2->tf_out[6] = (u_int64_t)(u_long)stack - (BIAS + CC64FSZ);
tf2->tf_in[6] = 0;
}
