linux-kernel - Re: [PATCH] coresight: fix the wrong type of the trace_id in coresight

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Message-ID: <CAJ9a7VinQSx9FYvw4ww0KQgMqapLhWTaU9D2qcc-120YywUu2Q@mail.gmail.com>
Date: Tue, 1 Apr 2025 10:56:30 +0100
From: Mike Leach <mike.leach@...aro.org>
To: Anshuman Khandual <anshuman.khandual@....com>
Cc: Jie Gan <jie.gan@....qualcomm.com>, Suzuki K Poulose <suzuki.poulose@....com>, 
	James Clark <james.clark@...aro.org>, Jie Gan <quic_jiegan@...cinc.com>, 
	Tingwei Zhang <quic_tingweiz@...cinc.com>, Jinlong Mao <quic_jinlmao@...cinc.com>, 
	coresight@...ts.linaro.org, linux-arm-kernel@...ts.infradead.org, 
	linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org, 
	Dan Carpenter <dan.carpenter@...aro.org>
Subject: Re: [PATCH] coresight: fix the wrong type of the trace_id in coresight_path

Hi,

On Tue, 1 Apr 2025 at 07:11, Anshuman Khandual
<anshuman.khandual@....com> 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@...aro.org>
> > Fixes: 3c03c49b2fa5 ("Coresight: Introduce a new struct coresight_path")
> > Signed-off-by: Jie Gan <jie.gan@....qualcomm.com>
>
> LGTM
>
> Reviewed-by: Anshuman Khandual <anshuman.khandual@....com>
>
> > ---
> >  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.

Regards

Mike



--
Mike Leach
Principal Engineer, ARM Ltd.
Manchester Design Centre. UK