change startup code to call munmap()/munmap_text() to map out

own 0-pages.

lib/i386/rts/crtso.s

@@ -1,3 +1,4 @@
+#
 ! This is the C run-time start-off routine.  It's job is to take the
 ! arguments as put on the stack by EXEC, and to parse them and set them up the
 ! way _main expects them.
@@ -6,6 +7,8 @@
 ! simplistic.  We simply check for some magic value, but there is no other
 ! way.
 
+#include <sys/vm_i386.h>
+
 .sect .text; .sect .rom; .sect .data; .sect .bss
 
 .define begtext, begdata, begbss
@@ -19,6 +22,7 @@ begdata:
 begbss:
 
 .define crtso, __penviron, __penvp, __fpu_present
+.define __minix_datastart, __minix_mainjump, __minix_unmapzero
 .extern _main, _exit
 .sect .text
 crtso:
@@ -49,6 +53,12 @@ crtso:
 	smsw	ax
 	testb	al, 0x4			! EM bit in MSW
 	setz	(__fpu_present)		! True if not set
+	jmp __minix_mainjump
+
+.align I386_PAGE_SIZE
+__minix_mainjump:
+	! unmap zero pages
+	call	__minix_unmapzero
 
 	call	_main			! main(argc, argv, envp)
 
@@ -57,10 +67,27 @@ crtso:
 
 	hlt				! force a trap if exit fails
 
+__minix_unmapzero:
+
+	! unmap 0-page code
+	push	I386_PAGE_SIZE
+	push	crtso
+	call	_munmap_text		! munmap_text(crtso, I386_PAGE_SIZE)
+	add	esp, 8
+
+	! unmap 0-page data
+	push	I386_PAGE_SIZE
+	push	romstart
+	call	_munmap			! munmap(romstart, I386_PAGE_SIZE)
+	add	esp, 8
+
+	ret
+
 .sect .rom
-	.data4	0			! Separate I&D: *NULL == 0
+romstart:
-					! Also keeps the first string in the
+	.space	I386_PAGE_SIZE
-					! program from appearing at location 0!
+__minix_datastart:
+	.space	4
 .sect .data
 __penviron:
 	.data4	__penvp			! Pointer to environ, or hidden pointer