Re: [Qemu-devel] [Bug] qemu-system-ppc: "invalid/unsupported opcode" during debug session

[Aurelien Jarno <aurelien@aurel32.net>]

On Sun, Feb 28, 2010 at 02:02:33PM +0000, Paul Brook wrote:
> > > invalid/unsupported opcode: 00 - 00 - 00 (00000000) 4800fa44 1
> > 
> > I have fixed that in HEAD by stopping the translation just after a trap,
> > as the instructions might never be executed.
> > 
> > It is not a full fix, as the OS can actually use any instruction that
> > always generate a trap (even a memory access) as an instruction barrier
> > to make sure the following instructions are never executed. This
> > actually affects all targets, but is unlikely to happen.
> > 
> > One solution for that would be to only generate an exception for an
> > unsupported instruction when it is the first instruction of a TB, and
> > otherwise just end the translation before this instruction.
> 
> By my reading the code is correct. We end up calling gen_invalid which output 
> code to raise an invalid instruction exception. If earlier code faults at 
> runtime then that code is never executed, and everything is happy.

You are correct, I have read the code too quickly. So ignore what I said
above.

> The real bug is that we have debugging printfs enabled by default.

Agreed, I'll fix that.

-- 
Aurelien Jarno	                        GPG: 1024D/F1BCDB73
aurelien@aurel32.net                 http://www.aurel32.net