Re: [Qemu-devel] [PATCH Risu 1/2] risu_ppc64: Fix Risu to run under qemu linux user

[joserz@linux.vnet.ibm.com]

On Mon, Jan 30, 2017 at 11:49:34AM +0000, Peter Maydell wrote:
> On 30 January 2017 at 02:47, Jose Ricardo Ziviani
> <joserz@linux.vnet.ibm.com> wrote:
> > Qemu linux-user doesn't fill uc_mcontext completely like full emul. does.
> > For instance, uc->uc_mcontext.regs->nip is an invalid so this
> > commit replaces it by uc->uc_mcontext.gp_regs[PT_NIP]
> 
> It's not clear to me from this commit message whether this is
> a bug in QEMU's userspace emulation which this is trying to work
> around (in which case we should just fix it in QEMU), or a
> bug in risu where we were incorrectly relying on something the
> kernel doesn't actually guarantee. Which is it?
> 
> Also, looking at the kernel source and headers as far
> as I can see uc_context.regs is a pointer set up such that
> uc->uc_mcontext.regs->nip is pointing at the same bit of
> memory where uc->uc_mcontext.gp_regs[PT_NIP] is,
> and the QEMU code does similar, so I don't see how you can
> get two different values from the two things.
> 
> (It is certainly the case that risu is quite good at exercising
> odd corner cases of the signal handling code in QEMU which most
> normal programs don't care about...)

Peter

I just sent a patch "linux-user: fill target sigcontext struct accordingly" to fix it in QEMU. Please, forget this patchset, I'll reorganize it and send it later.

Thank you

Ziviani