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

[Alexander Graf]

Am 30.12.2009 um 18:46 schrieb Aurelien Jarno <address@hidden>:

> On Wed, Dec 30, 2009 at 03:39:32PM +0100, Alexander Graf wrote:
> > Am 29.12.2009 um 22:07 schrieb Aurelien Jarno <address@hidden>:
> >
> > > On Tue, Dec 29, 2009 at 04:09:17PM +0100, Stefan Weil wrote:
> > > > Test environment:
> > > >
> > > > * ppc-softmmu/qemu-system-ppc running on x86_64 host
> > > > * emulated ppc is running debian lenny
> > > >
> > > >
> > > >
> > > > While debugging on the emulated ppc (each time when
> > > > a shared library is loaded after "r" command?),
> > > > qemu-system-ppc prints this error message:
> > > >
> > > > invalid/unsupported opcode: 00 - 00 - 00 (00000000) 4800fa44 1
> > > >
> > > >
> > > >
> > > > If logging is enabled, the error message goes to qemu.log:
> > > >
> > > > IN:
> > > > 0xc0013488:  nop
> > > > 0xc001348c:  rlwinm  r3,r3,0,0,19
> > > > 0xc0013490:  li      r4,128
> > > > 0xc0013494:  mtctr   r4
> > > > 0xc0013498:  mr      r6,r3
> > > > 0xc001349c:  dcbst   r0,r3
> > > >
> > > > invalid/unsupported opcode: 00 - 00 - 00 (00000000) 4800fa44 1
> > > > IN:
> > > > 0x4800fa40:  twge    r2,r2
> > > > 0x4800fa44:  .long 0x0
> > >
> > > The problem is that QEMU doesn't stop the decoding of instructions
> > > when
> > > it encounters a trap instruction. We should probably either end  
> > > the TB
> > > in that case, or avoid printing "invalid/unsupported opcode", as  
> > > this
> > > instruction will actually never been executed.
> >
> > Given how seldom they occur, it's probably best (easiest to read)  
> > to end
> > the TB.
>
> The question is to know if there are other conditions than branches  
> and
> trap where code can be translated, but then never executed.

We don't fix that by hacking the invalid opcode print either, because  
we'd still have to mark instructions we can't determine if an  
instruction is invalid later on.

IMHO the best solution would actually be to just not print out  
anything except for qemu.log if -d is used.

Alex
>