prevent files becoming larger than 2^32-1 bytes

Author: boeckmann

drdos/bdevio.asm

@@ -834,6 +834,19 @@ ifdef FATPLUS
 	mov	ax,byteoff+6
 	adc	ax,0
 	mov	fsize+6,ax
+else
+	 jnc	fdw_e03			; file size + fdrwcnt <4GB?
+	mov	ax,fsize		; otherwise restrict fdrwcnt
+	sbb	fdrwcnt,ax
+	 jnz	fdw_e02			; can write at least a single byte?
+	mov	ax,ED_ACCESS		; if not return access denied
+	jmp	fdos_error
+fdw_e02:
+	xor	ax,ax
+	dec	ax
+	mov	fsize,ax
+	mov	fsize+2,ax
+fdw_e03:
 endif
 ;	div	clsize			; AX whole blocks required
 ;	push	dx