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

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Message-ID: <CAJ9a7Vjhm5B=3mDHQpuRj2JSE1hfYzOx5wq-yQcC3k+QqEcvAQ@mail.gmail.com>
Date: Wed, 2 Apr 2025 09:17:31 +0100
From: Mike Leach <mike.leach@...aro.org>
To: Jie Gan <quic_jiegan@...cinc.com>
Cc: Anshuman Khandual <anshuman.khandual@....com>, Jie Gan <jie.gan@....qualcomm.com>, 
	Suzuki K Poulose <suzuki.poulose@....com>, James Clark <james.clark@...aro.org>, 
	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 Wed, 2 Apr 2025 at 01:50, Jie Gan <quic_jiegan@...cinc.com> wrote:
>
>
>
> On 4/1/2025 5:56 PM, Mike Leach wrote:
> > 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.
> >
>
> 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?

Mike

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


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