🚀 go-pugleaf

>>>
>>>Many people (including me, even) suggest the standard "jmp FFFF:0000"
>>>method.
>>>
>>>But this is extremely dangerous if the user is running disk cacheing
>>>software, since it bypasses *everything*!  Caches don't get flushed,
>>>and you run the risk of trashing your hard drive!
>

Well, what I've been telling people is:

------------------------------------------------------------------

The reboot program is reboot.com.  This program is created
from a debug script named reboot.dbg by typing "debug <reboot.dbg".
Reboot.dbg looks like this:

a 100
;cs:100
MOV	SI,0080                           ;point at command tail 
MOV	CX,[SI]                           ;get the length 
XOR	CH,CH                             ;check if it was zero 
JCXZ	0115                              ;if so, jmp 
INC	SI                                ;else get first char of arg 1 
INC	SI                                 
MOV	AL,[SI]                           ;into al 
CMP	AL,43                             ;was is 'C'?
JZ	011A                              ;if so, jmp 
CMP	AL,63                             ;was it 'c'? 
JZ	011A                              ;if so, jmp 
MOV	BX,1234                           ;set bx to magic number 1234 hex
JMP	011D                              ;and jmp 
;cs:11a
MOV	BX,7F7F                           ;else set bx to non-magic number 
;cs:11d
MOV	AX,0040                           
MOV	DS,AX                              
MOV	[0072],BX                         ;store bx in 0040:0072 
JMP	FFFF:0000                         ;and reboot 

n reboot.com
r bx
0
r cx
2b
w cs:100
q

------------------------------------------------------------------

A microsoft-c program to create reboot.exe which would do the same
thing is:

----------------------------------------------------------------

/* this program reboots the pc */
/* cold boot if an argument beginning with 'C' or 'c' is supplied */
/* warm boot otherwise */

#include <dos.h>
#include <ctype.h>

main(int argc, char **argv) {
	void (far *reboot)(void);
	int far *magic;

	FP_SEG(reboot) = 0xffff;
	FP_OFF(reboot) = 0;
	FP_SEG(magic) = 0x40;
	FP_OFF(magic) = 0x72;
	if (argc > 1 && tolower(*argv[1]) == 'c') {
		*magic = 0xffff;
	else
		*magic = 0x1234;
	}
	(*reboot)();		/* this should never return */
}

----------------------------------------------------------------

If there is any system-specific shutdown processing which needs to
be done (flushing the disk cache, idling the metal-stamping machine the
PC controls, whatever) it can/should be added.

Presumably, special measures will also be taken to assure that the
special shutdown processing gets done in case of ctl-alt-del reboot,
power fail/restore handling, trapping execution of illegal instructions,
vectoring thru unsupported interrupts, etc.

-- 
mitchell@mdd.comm.mot.com (Bill Mitchell)