One bonus of moving to ELF is that the boot loader on the sun2

now loads the kernel into physical memory at the linked address.
So we link the kernel a little lower virtually, but the bootloader
actually will load it higher in physical memory than before.
This allows us to quadruple the size of the msgbuf to 8K, and
we also shuffle around tmp_vpages and the temporary stack.

sys/arch/sun2/sun2/pmap.c

@@ -1,4 +1,4 @@
-/*	$NetBSD: pmap.c,v 1.8 2001/04/25 17:35:02 thorpej Exp $	*/
+/*	$NetBSD: pmap.c,v 1.9 2001/05/14 15:07:23 fredette Exp $	*/
 
 /*-
  * Copyright (c) 1996 The NetBSD Foundation, Inc.
@@ -216,8 +216,8 @@ static int temp_seg_inuse;
  * to be used in copy/zero operations.
  */
 vm_offset_t tmp_vpages[2] = {
-	KERNBASE + NBPG * 5,
+	NBPG * 8,
-	KERNBASE + NBPG * 6 };
+	NBPG * 9 };
 int tmp_vpages_inuse;
 
 static int pmap_version = 1;
@@ -793,17 +793,17 @@ pmeg_clean(pmegp)
 	int sme;
 	vm_offset_t va;
 
-	sme = get_segmap(0);
+	sme = get_segmap(temp_seg_va);
 	if (sme != SEGINV)
 		panic("pmeg_clean");
 
 	sme = pmegp->pmeg_index;
-	set_segmap(0, sme);
+	set_segmap(temp_seg_va, sme);
 
 	for (va = 0; va < NBSG; va += NBPG)
-		set_pte(va, PG_INVAL);
+		set_pte(temp_seg_va + va, PG_INVAL);
 
-	set_segmap(0, SEGINV);
+	set_segmap(temp_seg_va, SEGINV);
 }
 
 /*
@@ -1604,9 +1604,8 @@ pmap_bootstrap(nextva)
 
 	/*
 	 * Determine the range of physical memory available.
-	 * Physical memory at zero was remapped to KERNBASE.
 	 */
-	avail_start = nextva - KERNBASE;
+	avail_start = nextva;
 	avail_end = prom_memsize();
 	avail_end = m68k_trunc_page(avail_end);
 
@@ -1633,19 +1632,12 @@ pmap_bootstrap(nextva)
 	 */
 	pmeg_init();
 
-	/*
-	 * Unmap low virtual segments.
-	 * VA range: [0 .. KERNBASE]
-	 */
-	for (va = 0; va < KERNBASE; va += NBSG)
-		set_segmap(va, SEGINV);
-
 	/*
 	 * Reserve PMEGS for kernel text/data/bss
 	 * and the misc pages taken above.
 	 * VA range: [KERNBASE .. virtual_avail]
 	 */
-	for ( ; va < virtual_avail; va += NBSG) {
+	for (va = KERNBASE; va < virtual_avail; va += NBSG) {
 		sme = get_segmap(va);
 		if (sme == SEGINV) {
 			prom_printf("kernel text/data/bss not mapped\n");
@@ -1686,40 +1678,38 @@ pmap_bootstrap(nextva)
 	 */
 
 	/*
-	 * On both a Sun2 and Sun3, the kernel text starts at virtual
+	 * On a Sun2, the boot loader loads the kernel exactly where 
-	 * KERNTEXTOFF, physical 0x4000.  locore.s has set up a temporary
+	 * it is linked, at physical/virtual 0x6000 (KERNBASE).  This
-	 * stack starting at virtual (KERNTEXTOFF - sizeof(struct exec)),
+	 * means there are twelve physical/virtual pages before the
-	 * physical 0x3FE0, and growing down.
+	 * kernel text begins.
-	 *
-	 * On the Sun3, this means there are two physical pages before the
-	 * kernel text.  On the Sun3, page zero is reserved for the msgbuf
-	 * and page one contains the temporary stack.
-	 *
-	 * On the Sun2, there are eight physical pages before the kernel
-	 * text.  Pages 0-3 are used by the PROM.
 	 */
-	va = KERNBASE;
+	va = 0;
-	eva = KERNBASE + (NBPG * 4);
-	for(va = KERNBASE; va < eva; va += NBPG) {
-			pte = get_pte(va);
-			pte |= (PG_SYSTEM | PG_WRITE);
-			set_pte(va, pte);
-	}
 
 	/*
-	 * We start the msgbuf at page four.
+	 * Physical/virtual pages zero through three are used by the 
+	 * PROM.  prom_init has already saved the PTEs, now we get
+	 * to unmap the pages.
 	 */
-	pte = get_pte(va);
+	eva = va + NBPG * 4;
-	pte |= (PG_SYSTEM | PG_WRITE | PG_NC);
+	for(; va < eva; va += NBPG)
-	set_pte(va, pte);
+		set_pte(va, PG_INVAL);
-	va += NBPG;
+
+	/*
+	 * We use pages four through seven for the msgbuf.
+	 */
+	eva = va + NBPG * 4;
+	for(; va < eva; va += NBPG) {
+		pte = get_pte(va);
+		pte |= (PG_SYSTEM | PG_WRITE | PG_NC);
+		set_pte(va, pte);
+	}
 	/* Initialize msgbufaddr later, in machdep.c */
 
 	/*
 	 * On the Sun3, two of the three dead pages in SUN3_MONSHORTSEG
 	 * are used for tmp_vpages.  The Sun2 doesn't have this
-	 * short-segment concept, so we reserve virtual pages five and six
+	 * short-segment concept, so we reserve virtual pages eight 
-	 * after KERNBASE for this.
+	 * and nine for this.
 	 */
 	set_pte(va, PG_INVAL);
 	va += NBPG;
@@ -1727,14 +1717,16 @@ pmap_bootstrap(nextva)
 	va += NBPG;
 
 	/*
-	 * Page seven remains for the temporary kernel stack.  Hopefully
+	 * Pages ten and eleven remain for the temporary kernel stack,
-	 * this is enough space.
+	 * which is set up by locore.s.  Hopefully this is enough space.
 	 */
-	pte = get_pte(va);
+	eva = va + NBPG * 2;
-	pte &= ~(PG_NC);
+	for(; va < eva ; va += NBPG) {
-	pte |= (PG_SYSTEM | PG_WRITE);
+		pte = get_pte(va);
-	set_pte(va, pte);
+		pte &= ~(PG_NC);
-	va += NBPG;
+		pte |= (PG_SYSTEM | PG_WRITE);
+		set_pte(va, pte);
+	}
 
 	/*
 	 * Next is the kernel text.