WinUAE Enforcer hit: illegal read from 0 by ROM = bug ?

[PeterK]

How should I rate an Enforcer hit "illegal read from $00000000" = CMP.L (0).w, D0 if it's done by the ROM 40.68 A1200 at $00F8357C or A4000 at $00F83584 ? Is this really a bug ? (Sorry, the log files are already overwritten) I'm using WinUAE 3.5.0 x64

[ross]

Originally Posted by PeterK

How should I rate an Enforcer hit "illegal read from $00000000" = CMP.L (0).w, D0 if it's done by the ROM 40.68 A1200 at $00F8357C or A4000 at $00F83584 ? Is this really a bug ? (Sorry, the log files are already overwritten) I'm using WinUAE 3.5.0 x64

Is somewhere related to 'HELP' string in $0 by a catastrophic failure?

[Tomislav]

Exec Alert() function is in that part of ROM.
Do you mean Enforcer debugging tool by Michael Sinz? Last version is V37.73.
WinUAE configuration?

[thellier]

Certainly a null pointer is given to some ROM function
So the error is in the program/function that call it (in the program not in ROM)
So just check in the enforcer log what stack was before the call to $00F8357C

[Toni Wilen]

00F83576 203c 4845 4c50           MOVE.L #$48454c50,D0
00F8357C b0b8 0000                CMP.L $0000,D0

Obviously "HELP" check.

[PeterK]

Yes ok, it's a "HELP" check, whatever it's doing. Since I have no ROM documentation and don't want to reverse engineer that routine, it's unclear what exactly the purpose of this check at address 0 is.

But my question was more why it should be an illegal access to Null if this is a hard coded address and it's done by the ROM. The ROM should be allowed to do that. But maybe the coders indeed wanted to cause an Enforcer hit to get attention when this code is ever executed. Unfortunately, I can not reproduce this hit and don't have the Enforcer logs anymore.

Thanks for all replies.

[a4k-oerx]

Originally Posted by PeterK

Yes ok, it's a "HELP" check, whatever it's doing. Since I have no ROM documentation and don't want to reverse engineer that routine...

Maybe the "AmigaOS 1.2 Exec, disassembled and commented" on this page helps, search for the string there..

[PeterK]

Thx for your help, a4k-oerx!

See if the system wants a guru put up after reboot.

This works as follows: If for some reason, a guru can't be put
up in the normal fashion, the system writes "HELP" at location
zero, writes the alert data (number and 32-bit parameter) at
location $000100, and resets.

Early in the startup code (right here), this "HELP" is checked
for. If it is present, it is removed, and the data at location
$000100 is loaded into registers D6 and D7. If no "HELP" is
found, register D6 is loaded with -1. This data will later be
put at ExecBase->LastAlert, once the ExecBase structure has been
built. The following subroutine call does all this.

Check whether there is already a valid ExecBase data structure.
This is important, since it indicates whether we need to clear and
reconfigure memory (wiping out recoverable RAM disks and such),
or whether we already know the memory configuration and can leave
it untouched.

Note that if the machine crashed in such a way that the ExecBase
structure got clobbered, memory will be cleared.

Btw, my Enforcer hits under WB 3.0/3.1 are fixed now.