In cpu_fork() do not copy the register windows stashed in the u_pcb

if the new proc has its own stack. In that case the new thread starts
with a fresh stack and there are no register windows to spill back.

This fixes the pthread issues that kurt@ was struggling with for a long
time. Depending on the scheduler a thread would stomp over another threads
stack which caused strange crashes.

Improved diff provided by miod@
OK miod@ mpi@ kurt@

diff --git a/sys/arch/sparc64/sparc64/vm_machdep.c b/sys/arch/sparc64/sparc64/vm_machdep.c
index 4a7ecb9..c5016ae 100644 (file)
--- a/sys/arch/sparc64/sparc64/vm_machdep.c
+++ b/sys/arch/sparc64/sparc64/vm_machdep.c
@@ -1,4 +1,4 @@
-/*     $OpenBSD: vm_machdep.c,v 1.42 2022/10/25 06:05:57 guenther Exp $        */
+/*     $OpenBSD: vm_machdep.c,v 1.43 2024/02/19 09:59:29 claudio Exp $ */
 /*     $NetBSD: vm_machdep.c,v 1.38 2001/06/30 00:02:20 eeh Exp $ */
 
 /*
@@ -100,6 +100,7 @@ cpu_fork(struct proc *p1, struct proc *p2, void *stack, void *tcb,
        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 *p2, void *stack, void *tcb,
 #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 *p2, void *stack, void *tcb,
         * 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;
        }