Fix LWP's stack initialization for -s

With -s, LWP initializes thread stacks to track stack use.  It did
that after makecontext(), with disastrous results on systems where
makecontext() writes something to the stack that swapcontext() expects
to find there.  Makes FreeBSD 6.2 crash in swapcontext().

Factor stack allocation out of lwpNewContext() into lwpNewStack().
Move call of lwpStackCheckInit() into lwpNewStack().

src/lib/lwp/arch.c

@@ -47,36 +47,16 @@
  */
 
 int
-lwpNewContext(struct lwpProc *newp, int stacksz)
+lwpNewContext(struct lwpProc *newp)
 {
-    char *s;
-    int size, redsize;
-
-    /* Make size a multiple of sizeof(long) to keep things aligned */
-    stacksz = (stacksz + sizeof(long) - 1) & -sizeof(long);
-    /* Add a red zone on each side of the stack for LWP_STACKCHECK */
-    redsize = newp->flags & LWP_STACKCHECK ? LWP_REDZONE : 0;
-    size = stacksz + 2 * redsize;
-
-    s = malloc(size);
-    if (!s)
+    if (getcontext(&newp->context) < 0)
 	return -1;
-
-    newp->sbtm = s;
-    newp->size = size;
-    newp->ustack = s + redsize;
-    newp->usize = stacksz;
-
-    if (getcontext(&newp->context) < 0) {
-	free(s);
-	return -1;
-    }
 #ifdef MAKECONTEXT_SP_HIGH
     /*
      * Known systems that are broken that way: Solaris prior to 10,
      * IRIX.
      */
-    newp->context.uc_stack.ss_sp = newp->ustack + stacksz - 8;
+    newp->context.uc_stack.ss_sp = newp->ustack + newp->usize - 8;
 #else
     newp->context.uc_stack.ss_sp = newp->ustack;
 #endif

src/lib/lwp/lwp.c

@@ -127,6 +127,32 @@ lwpEntryPoint(void)
     lwpExit();
 }
 
+static int
+lwpNewStack(struct lwpProc *newp, int stacksz)
+{
+    char *s;
+    int size, redsize;
+
+    /* Make size a multiple of sizeof(long) to keep things aligned */
+    stacksz = (stacksz + sizeof(long) - 1) & -sizeof(long);
+    /* Add a red zone on each side of the stack for LWP_STACKCHECK */
+    redsize = newp->flags & LWP_STACKCHECK ? LWP_REDZONE : 0;
+    size = stacksz + 2 * redsize;
+
+    s = malloc(size);
+    if (!s)
+	return -1;
+
+    newp->sbtm = s;
+    newp->size = size;
+    newp->ustack = s + redsize;
+    newp->usize = stacksz;
+
+    if (newp->flags & LWP_STACKCHECK)
+	lwpStackCheckInit(newp);
+    return 0;
+}
+
 /*
  * lwpCreate -- create a process.
  */
@@ -147,19 +173,19 @@ lwpCreate(int priority, void (*entry)(void *), int stacksz,
     newp->dead = 0;
     newp->runtime = (time_t)-1;
     newp->fd = -1;
+    newp->sbtm = NULL;
     if (LWP_MAX_PRIO <= priority)
 	priority = LWP_MAX_PRIO - 1;
     if (LwpMaxpri < (newp->pri = priority))
 	LwpMaxpri = priority;
-    if (lwpNewContext(newp, stacksz) < 0) {
+    if (lwpNewStack(newp, stacksz) < 0 || lwpNewContext(newp) < 0) {
+	free(newp->sbtm);
 	free(newp->name);
 	free(newp);
 	return NULL;
     }
     lwpStatus(newp, "creating process structure %p (sbtm %p)",
 	      newp, newp->sbtm);
-    if (flags & LWP_STACKCHECK)
-	lwpStackCheckInit(newp);
     lwpReady(newp);
     lwpReady(LwpCurrent);
     lwpReschedule();

src/lib/lwp/lwpint.h

@@ -73,7 +73,7 @@ struct lwpQueue {
 
 extern int LwpStackGrowsDown;
 
-int lwpNewContext(struct lwpProc *, int);
+int lwpNewContext(struct lwpProc *);
 void lwpSwitchContext(struct lwpProc *, struct lwpProc *);
 void lwpAddTail(struct lwpQueue *, struct lwpProc *);
 struct lwpProc *lwpGetFirst(struct lwpQueue *);