Sorry for the longish To list, not sure who's responsible for this
particular piece. (And if I got it wrong even after all that, please let
me know..)

This is for 2.4; in 2.5 reboot.c has identical code with an identical
problem. (I'll send a separate patch after getting feedback on this
one.)

If you don't pass reboot=, reboot_mode and reboot_thru_bios are used
uninitialized and (in the case of reboot_mode) written directly to
memory for the bios.

This patch sets reboot_mode to 0x1234 by default, and reboot_thru_bios
(used in "if(!reboot_thru_bios)") to 1.

void machine_restart(char * __unused)
{
..[smp shutdown]..
  if(!reboot_thru_bios) {
        /* rebooting needs to touch the page at absolute addr 0 */
        *((unsigned short *)__va(0x472)) = reboot_mode;
...
        machine_real_restart(jump_to_bios, sizeof(jump_to_bios));
}

void machine_real_restart(unsigned char *code, int length)
{
.....
  /* Write 0x1234 to absolute memory location 0x472.  The BIOS reads
     this on booting to tell it to "Bypass memory test (also warm
     boot)".  This seems like a fairly standard thing that gets set by
     REBOOT.COM programs, and the previous reset routine did this
     too. */

  *((unsigned short *)0x472) = reboot_mode;
...
}


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