Re: [PATCH] coresight: fix the wrong type of the trace_id in coresight_path

[Jie Gan]

On 4/2/2025 4:17 PM, Mike Leach wrote:
> Hi,
>
> On Wed, 2 Apr 2025 at 01:50, Jie Gan <quic_jiegan@xxxxxxxxxxx> wrote:
> > On 4/1/2025 5:56 PM, Mike Leach wrote:
> > > Hi,
> > >
> > > On Tue, 1 Apr 2025 at 07:11, Anshuman Khandual
> > > <anshuman.khandual@xxxxxxx> wrote:
> > > > On 4/1/25 07:12, Jie Gan wrote:
> > > > > The trace_id in coresight_path may contain an error number which means a
> > > > > negative integer, but the current type of the trace_id is u8. Change the
> > > > > type to int to fix it.
> > > > >
> > > > > Reported-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
> > > > > Fixes: 3c03c49b2fa5 ("Coresight: Introduce a new struct coresight_path")
> > > > > Signed-off-by: Jie Gan <jie.gan@xxxxxxxxxxxxxxxx>
> > > >
> > > > LGTM
> > > >
> > > > Reviewed-by: Anshuman Khandual <anshuman.khandual@xxxxxxx>
> > > >
> > > > > ---
> > > > >    include/linux/coresight.h | 2 +-
> > > > >    1 file changed, 1 insertion(+), 1 deletion(-)
> > > > >
> > > > > diff --git a/include/linux/coresight.h b/include/linux/coresight.h
> > > > > index d79a242b271d..c2bf10c43e7c 100644
> > > > > --- a/include/linux/coresight.h
> > > > > +++ b/include/linux/coresight.h
> > > > > @@ -337,7 +337,7 @@ static struct coresight_dev_list (var) = {                                \
> > > > >     */
> > > > >    struct coresight_path {
> > > > >         struct list_head        path_list;
> > > > > -     u8                      trace_id;
> > > > > +     int                     trace_id;
> > > > >    };
> > > > >
> > > > >    enum cs_mode {
> > >
> > > There are many places in the Coresight drivers that assign a u8
> > > traceid from the path trace ID.
> > >
> > > e.g.
> > > In coresight-etm4x-core.c : etm4_enable_perf()
> > >
> > > drvdata->trcid = path->trace_id;
> > >
> > > drvdata->trcid is defined as a u8  - the reason being trace IDs are
> > > 128 bits wide with some reserved values.
> > >
> > > Will this not just trigger the same issue if path->trace_id is changed
> > > to an int? Even if not it is inconsistent handling of the trace ID
> > > values.
> > >
> > > Trace ID errors should be handled by returning an invalid trace ID
> > > value - were the trace ID value will fail the macro
> > > IS_VALID_CS_TRACE_ID(), or separate the return of a trace ID from an
> > > error return in a function.
> >
> > Hi Mike,
> >
> > The path->trace_id is verified after it has been assigned with the logic
> > you mentioned:
> >
> > if (!IS_VALID_CS_TRACE_ID(path->trace_id))
> >          goto err_path;
> >
> > So it should be safe to assign to another u8 parameter, like you mentioned:
> >
> > In coresight-etm4x-core.c : etm4_enable_perf()
> >
> > drvdata->trcid = path->trace_id;
>
> It is safe but will it not trigger a warning just like the one you are
> trying to fix as the types are mismatched?

Hi Mike,

It should trigger another type mismatch warning.

This patch aims to fix the situation like assign a negative value to u8 
will cause a integer toggle(it may happen and I think I should fix it), 
e.g. -22 for 234.

Thanks,
Jie

> Mike
>
> > Thanks,
> > Jie
> >
> >
> > > Regards
> > >
> > > Mike
> > >
> > >
> > >
> > > --
> > > Mike Leach
> > > Principal Engineer, ARM Ltd.
> > > Manchester Design Centre. UK