Re: [Qemu-devel] [PATCH] target-s390x: Mask the SIGP order_code to 8bit.

[Philipp Kern]

On 2017-04-25 11:51, Richard Henderson wrote:
> On 04/24/2017 10:25 AM, Alexander Graf wrote:
> > On 24.04.17 00:32, Aurelien Jarno wrote:
> > > From: Philipp Kern <address@hidden>
> > >
> > > According to "CPU Signaling and Response", "Signal-Processor Orders",
> > > the order field is bit position 56-63. Without this, the Linux
> > > guest kernel is sometimes unable to stop emulation and enters
> > > an infinite loop of "XXX unknown sigp: 0xffffffff00000005".
> > >
> > > Signed-off-by: Philipp Kern <address@hidden>
> > > Signed-off-by: Aurelien Jarno <address@hidden>
> > > ---
> > >  target/s390x/misc_helper.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > This patch has been sent by Philipp Kern a lot of time ago, and it 
> > > seems
> > > has been lost. I am resending it, as it is still useful.
> > >
> > > diff --git a/target/s390x/misc_helper.c b/target/s390x/misc_helper.c
> > > index 3bf09ea222..4946b56ab3 100644
> > > --- a/target/s390x/misc_helper.c
> > > +++ b/target/s390x/misc_helper.c
> > > @@ -534,7 +534,7 @@ uint32_t HELPER(sigp)(CPUS390XState *env, 
> > > uint64_t order_code, uint32_t r1,
> > >      /* Remember: Use "R1 or R1 + 1, whichever is the odd-numbered 
> > > register"
> > >         as parameter (input). Status (output) is always R1. */
> > >
> > > -    switch (order_code) {
> > > +    switch (order_code & 0xff) {
> >
> > This definitely needs a comment above the mask. Ideally I'd love to 
> > just change the function prototype to pass order_code as uint8_t, but 
> > I don't think that's possible with the TCG glue.
>
> Correct.  We'll need to leave the mask here.

I shall point out that Alexander merged it into the s390-next tree when 
I first sent it but that was never merged into qemu proper. I don't 
think there's a problem in adding a comment that says what the commit 
description says right there, like this:

/* sigp contains the order code in bit positions 56-63, mask it here. */

Kind regards
Philipp Kern