--- /sys/src/9/bcm/main.c	Sat Jan 26 00:19:03 2013
+++ /sys/src/9/bcm/main.c	Fri Jul 26 00:49:36 2013
@@ -10,6 +10,11 @@
 
 #include "reboot.h"
 
+enum {
+	/* space for syscall args, return PC, top-of-stack struct */
+	Ustkheadroom	= sizeof(Sargs) + sizeof(uintptr) + sizeof(Tos),
+};
+
 /* Firmware compatibility */
 #define	Minfirmrev	326770
 #define	Minfirmdate	"22 Jul 2012"
@@ -326,7 +331,7 @@
 	 * of the argument list checked in syscall.
 	 */
 	i = oargblen+1;
-	p = UINT2PTR(STACKALIGN(base + BY2PG - sizeof(Tos) - i));
+	p = UINT2PTR(STACKALIGN(base + BY2PG - Ustkheadroom - i));
 	memmove(p, oargb, i);
 
 	/*
--- /sys/src/9/kw/main.c	Tue Jul 26 18:46:45 2011
+++ /sys/src/9/kw/main.c	Fri Jul 26 00:46:17 2013
@@ -7,6 +7,7 @@
 #include "init.h"
 #include "arm.h"
 #include <pool.h>
+#include <tos.h>
 
 #include "reboot.h"
 
@@ -24,6 +25,9 @@
 enum {
 	Maxmem	= 512*MB,			/* limited by address ranges */
 	Minmem	= 256*MB,			/* conservative default */
+
+	/* space for syscall args, return PC, top-of-stack struct */
+	Ustkheadroom	= sizeof(Sargs) + sizeof(uintptr) + sizeof(Tos),
 };
 
 #define isascii(c) ((uchar)(c) > 0 && (uchar)(c) < 0177)
@@ -515,7 +519,7 @@
 	 * of the argument list checked in syscall.
 	 */
 	i = oargblen+1;
-	p = UINT2PTR(STACKALIGN(base + BY2PG - sizeof(up->s.args) - i));
+	p = UINT2PTR(STACKALIGN(base + BY2PG - Ustkheadroom - i));
 	memmove(p, oargb, i);
 
 	/*
--- /sys/src/9/omap/main.c	Tue Jan 18 00:58:06 2011
+++ /sys/src/9/omap/main.c	Fri Jul 26 00:46:17 2013
@@ -7,6 +7,7 @@
 
 #include "init.h"
 #include <pool.h>
+#include <tos.h>
 
 #include "reboot.h"
 
@@ -23,8 +24,12 @@
 
 enum {
 	Minmem	= 256*MB,			/* conservative default */
+
+	/* space for syscall args, return PC, top-of-stack struct */
+	Ustkheadroom	= sizeof(Sargs) + sizeof(uintptr) + sizeof(Tos),
 };
 
+
 #define isascii(c) ((uchar)(c) > 0 && (uchar)(c) < 0177)
 
 uintptr kseg0 = KZERO;
@@ -485,7 +490,7 @@
 	 * of the argument list checked in syscall.
 	 */
 	i = oargblen+1;
-	p = UINT2PTR(STACKALIGN(base + BY2PG - sizeof(up->s.args) - i));
+	p = UINT2PTR(STACKALIGN(base + BY2PG - Ustkheadroom - i));
 	memmove(p, oargb, i);
 
 	/*
--- /sys/src/9/pc/main.c	Thu Jun 13 23:02:40 2013
+++ /sys/src/9/pc/main.c	Fri Jul 26 00:28:23 2013
@@ -9,6 +9,7 @@
 #include	"pool.h"
 #include	"reboot.h"
 #include	"mp.h"
+#include	<tos.h>
 
 Mach *m;
 
@@ -24,6 +25,11 @@
 #define	BOOTARGSLEN	(4096-0x200-BOOTLINELEN)
 #define	MAXCONF		64
 
+enum {
+	/* space for syscall args, return PC, top-of-stack struct */
+	Ustkheadroom	= sizeof(Sargs) + sizeof(uintptr) + sizeof(Tos),
+};
+
 char bootdisk[KNAMELEN];
 Conf conf;
 char *confname[MAXCONF];
@@ -306,7 +312,7 @@
 	char *cp = BOOTLINE;
 	char buf[64];
 
-	sp = (uchar*)base + BY2PG - MAXSYSARG*BY2WD;
+	sp = (uchar*)base + BY2PG - Ustkheadroom;
 
 	ac = 0;
 	av[ac++] = pusharg("/386/9dos");
@@ -414,8 +420,8 @@
 		 * The patch of nimage is a band-aid, scanning the whole
 		 * page list in imagereclaim just takes too long.
 		 */
-		if(kpages > (64*MB + conf.npage*sizeof(Page))/BY2PG){
-			kpages = (64*MB + conf.npage*sizeof(Page))/BY2PG;
+		if(kpages > (128*MB + conf.npage*sizeof(Page))/BY2PG){
+			kpages = (128*MB + conf.npage*sizeof(Page))/BY2PG;
 			conf.nimage = 2000;
 			kpages += (conf.nproc*KSTACK)/BY2PG;
 		}
--- /sys/src/9/pcboot/main.c	Thu May 31 20:22:47 2012
+++ /sys/src/9/pcboot/main.c	Fri Jul 26 00:45:57 2013
@@ -16,9 +16,13 @@
 #include	"pool.h"
 #include	"reboot.h"
 #include	"ip.h"		/* for eipfmt */
+#include	<tos.h>
 
 enum {
 	Datamagic = 0xbabeabed,
+
+	/* space for syscall args, return PC, top-of-stack struct */
+	Ustkheadroom	= sizeof(Sargs) + sizeof(uintptr) + sizeof(Tos),
 };
 
 Mach *m;
@@ -343,7 +347,7 @@
 	return sp;
 }
 
-/* we're a bootstrap loader, so we aren't passed any options. */
+/* we're a bootstrap loader, so we aren't passed any options to pass on. */
 void
 bootargs(void *base)
 {
@@ -353,7 +357,7 @@
 	char *cp = "";
 	char buf[64];
 
-	sp = (uchar*)base + BY2PG - MAXSYSARG*BY2WD;
+	sp = (uchar*)base + BY2PG - Ustkheadroom;
 
 	ac = 0;
 	av[ac++] = pusharg("/386/9dos");
--- /sys/src/9/rb/main.c	Tue Jul 23 03:48:59 2013
+++ /sys/src/9/rb/main.c	Fri Jul 26 00:46:17 2013
@@ -11,6 +11,11 @@
 #include	<bootexec.h>
 #include	"reboot.h"
 
+enum {
+	/* space for syscall args, return PC, top-of-stack struct */
+	Stkheadroom	= sizeof(Sargs) + sizeof(uintptr) + sizeof(Tos),
+};
+
 typedef struct mipsexec Mipsexec;
 
 /*
@@ -283,7 +288,7 @@
 	 * of the argument list checked in syscall.
 	 */
 	i = oargblen+1;
-	p = UINT2PTR(STACKALIGN(base + BY2PG - sizeof(Tos) - i));
+	p = UINT2PTR(STACKALIGN(base + BY2PG - Stkheadroom - i));
 	memmove(p, oargb, i);
 
 	/*
@@ -329,7 +334,7 @@
 	 * Kernel Stack
 	 */
 	p->sched.pc = (ulong)init0;
-	p->sched.sp = (ulong)p->kstack+KSTACK-(sizeof(Sargs)+BY2WD);
+	p->sched.sp = (ulong)p->kstack+KSTACK-Stkheadroom;
 	p->sched.sp = STACKALIGN(p->sched.sp);
 
 	/*
--- /sys/src/9/teg2/main.c	Tue May  1 22:57:57 2012
+++ /sys/src/9/teg2/main.c	Fri Jul 26 00:33:01 2013
@@ -7,6 +7,7 @@
 
 #include "init.h"
 #include <pool.h>
+#include <tos.h>
 
 #include "arm.h"
 #include "reboot.h"
@@ -24,6 +25,9 @@
 
 enum {
 	Minmem	= 256*MB,			/* conservative default */
+
+	/* space for syscall args, return PC, top-of-stack struct */
+	Ustkheadroom	= sizeof(Sargs) + sizeof(uintptr) + sizeof(Tos),
 };
 
 #define isascii(c) ((uchar)(c) > 0 && (uchar)(c) < 0177)
@@ -714,7 +718,7 @@
 	 * of the argument list checked in syscall.
 	 */
 	i = oargblen+1;
-	p = UINT2PTR(STACKALIGN(base + BY2PG - sizeof(up->s.args) - i));
+	p = UINT2PTR(STACKALIGN(base + BY2PG - Ustkheadroom));
 	memmove(p, oargb, i);
 
 	/*