Re: [PATCH 2/2] KVM: arm/arm64: Print the EC hex value with its exact width

[Zenghui Yu]

Hi Marc,

On 2019/9/11 16:31, Marc Zyngier wrote:
> On Wed, 11 Sep 2019 03:33:36 +0100,
> Zenghui Yu <yuzenghui@xxxxxxxxxx> wrote:
> > EC is the bits [31:26] of ESR_ELx on arm64 (HSR on arm). Print the
> > hex value with its exact width (8).
> >
> > Signed-off-by: Zenghui Yu <yuzenghui@xxxxxxxxxx>
> > ---
> >   virt/kvm/arm/trace.h | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/virt/kvm/arm/trace.h b/virt/kvm/arm/trace.h
> > index 204d210d01c2..022b0a060034 100644
> > --- a/virt/kvm/arm/trace.h
> > +++ b/virt/kvm/arm/trace.h
> > @@ -42,7 +42,7 @@ TRACE_EVENT(kvm_exit,
> >   		__entry->vcpu_pc		= vcpu_pc;
> >   	),
> >   
> > -	TP_printk("%s: HSR_EC: 0x%04x (%s), PC: 0x%08lx",
> > +	TP_printk("%s: HSR_EC: 0x%02x (%s), PC: 0x%08lx",
> >   		  __print_symbolic(__entry->ret, kvm_arm_exception_type),
> >   		  __entry->esr_ec,
> >   		  __print_symbolic(__entry->esr_ec, kvm_arm_exception_class),
>
> Although you're right that 8 bits ought to be enough, this is a change
> to the output of the tracepoint, which userspace could (does?) parse.

Well-written userspace tools should only parse the low 8 bits (if they
do parse). But even if the high bits are parsed, they're always 0.
So I don't think this change will have a bad impact on userspace.

> I'm thus reluctant to change anything there, knowing that we don't
> lose any information, and just print two extra zeroes.

Anyway this is not a fix, feel free to ignore it if you're worried about
that there might be some issues ;)

> Am I missing anything?

No.


Thanks,
zenghui