libthread: use mmap to allocate OpenBSD stacks

Should fix faults on OpenBSD.

Fixes #218.
Fixes #226.

src/libthread/Darwin-x86_64-swapcontext.c

@@ -16,6 +16,14 @@ makecontext(ucontext_t *uc, void (*fn)(void), int argc, ...)
 	va_end(arg);
 
 	sp = (uintptr*)((char*)uc->uc_stack.ss_sp+uc->uc_stack.ss_size);
+	/*
+	 * Stack pointer at call instruction (before return address
+	 * gets pushed) must be 16-byte aligned.
+	 */
+	if((uintptr)sp%4)
+		abort();
+	while((uintptr)sp%16 != 0)
+		sp--;
 	*--sp = 0;  // fn's return address
 	*--sp = (uintptr)fn;  // return address of setcontext
 	uc->mc.sp = (uintptr)sp;

src/libthread/stkmalloc.c

@@ -0,0 +1,13 @@
+#include "threadimpl.h"
+
+void*
+_threadstkalloc(int n)
+{
+	return malloc(n);
+}
+
+void
+_threadstkfree(void *v, int n)
+{
+	free(v);
+}

src/libthread/stkmmap.c

@@ -0,0 +1,25 @@
+#include <u.h>
+#include <sys/mman.h>
+#include "threadimpl.h"
+
+#ifndef MAP_STACK
+#define MAP_STACK 0
+#endif
+
+void*
+_threadstkalloc(int n)
+{
+	void *p;
+
+	p = mmap(nil, n, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANON|MAP_STACK, -1, 0);
+	if(p == (void*)-1)
+		return nil;
+	return p;
+}
+
+void
+_threadstkfree(void *v, int n)
+{
+	if(n > 0)
+		munmap(v, n);
+}

src/libthread/sysofiles.sh

@@ -6,22 +6,22 @@ tag="$OBJTYPE-$SYSNAME-${SYSVERSION:-`uname -r`}-${CC9:-cc}"
 case "$tag" in
 *-Linux-2.[0-5]*)
 	# will have to fix this for linux power pc
-	echo ${SYSNAME}-${OBJTYPE}-asm.o $SYSNAME.o
+	echo ${SYSNAME}-${OBJTYPE}-asm.o $SYSNAME.o stkmalloc.o
 	;;
 *-FreeBSD-[0-4].*)
-	echo ${SYSNAME}-${OBJTYPE}-asm.o $SYSNAME.o
+	echo ${SYSNAME}-${OBJTYPE}-asm.o $SYSNAME.o stkmalloc.o
 	;;
 *-NetBSD-*)
-	echo ${SYSNAME}-${OBJTYPE}-asm.o $SYSNAME.o
+	echo ${SYSNAME}-${OBJTYPE}-asm.o $SYSNAME.o stkmalloc.o
 	;;
 *-Darwin-10.[5-6].* | *-Darwin-[89].*)
-	echo ${SYSNAME}-${OBJTYPE}-asm.o $SYSNAME-${OBJTYPE}.o pthread.o
+	echo ${SYSNAME}-${OBJTYPE}-asm.o $SYSNAME-${OBJTYPE}.o pthread.o stkmalloc.o
 	;;
 *-OpenBSD-*)
-	echo ${SYSNAME}-${OBJTYPE}-asm.o ${SYSNAME}-${OBJTYPE}.o pthread.o
+	echo ${SYSNAME}-${OBJTYPE}-asm.o ${SYSNAME}-${OBJTYPE}.o pthread.o stkmmap.o
 	;;
 *)
-	echo pthread.o
+	echo pthread.o stkmalloc.o
 esac
 
 case "$OBJTYPE-$SYSNAME" in

src/libthread/thread.c

@@ -109,7 +109,7 @@ threadalloc(void (*fn)(void*), void *arg, uint stack)
 	ulong z;
 
 	/* allocate the task and stack together */
-	t = malloc(sizeof *t+stack);
+	t = malloc(sizeof *t);
 	if(t == nil)
 		sysfatal("threadalloc malloc: %r");
 	memset(t, 0, sizeof *t);
@@ -122,7 +122,9 @@ threadalloc(void (*fn)(void*), void *arg, uint stack)
 	/* do a reasonable initialization */
 	if(stack == 0)
 		return t;
-	t->stk = (uchar*)(t+1);
+	t->stk = _threadstkalloc(stack);
+	if(t->stk == nil)
+		sysfatal("threadalloc malloc stack: %r");
 	t->stksize = stack;
 	memset(&t->context.uc, 0, sizeof t->context.uc);
 	sigemptyset(&zero);
@@ -353,6 +355,7 @@ Top:
 		delthreadinproc(p, t);
 		p->nthread--;
 /*print("nthread %d\n", p->nthread); */
+		_threadstkfree(t->stk, t->stksize);
 		free(t);
 	}
 
@@ -509,6 +512,8 @@ needstack(int n)
 	_Thread *t;
 
 	t = proc()->thread;
+	if(t->stk == nil)
+		return;
 
 	if((char*)&t <= (char*)t->stk
 	|| (char*)&t - (char*)t->stk < 256+n){

src/libthread/threadimpl.h

@@ -209,3 +209,5 @@ extern void _threadsetupdaemonize(void);
 extern void _threaddodaemonize(char*);
 extern void _threadpexit(void);
 extern void _threaddaemonize(void);
+extern void *_threadstkalloc(int);
+extern void _threadstkfree(void*, int);