Re: [Qemu-devel] Sparc32 bash problem solved

[Blue Swirl]

> > emulator. I finally found the reason by observing strange Linux 
> behaviour
> > relating to MMU no-fault mode. No fault mode seems to apply only to
> > supervisor accesses, not user ones. The logic was not described like 
> this
> > in the manual, thank you very much.
>
> How did you find it?

I looked at qemu.log to find the faulting location in bash. I enabled 
DEBUG_MMU in helper.c and op_helper.c to see if the MMU mappings are 
correct, generating some 400 megs of logs. The instruction was load and the 
data being accessed was not mapped. Then I attached gdb to emulator and set 
a breakpoint to the faulting address and also to Linux fault handler. I 
noticed that the fault kept repeating forever, as if Linux didn't realise 
that any fault has happened. Then I got the idea to try this change. I think 
the logic is that it is not safe to allow user to override the MMU mappings. 
What an exciting story to tell your grandchildren, don't you think?

> Caller[f0005e0c]: t_sec_trap_start_interrupt+0x38/0x5c
> Caller[f01096c4]: prom_nbputchar+0xa0/0xb0

Maybe there is something wrong with Proll putchar function, or Proll's data 
areas are overwritten.

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