linux-kernel - Re: [PATCH] coresight: etm3x: Fix buffer overwrite in cntr_val

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Message-ID: <CAJ9a7Vjia4ENewP48nyDWBcBFbDmwb3vM2JNbNCw4-3yF3ABVQ@mail.gmail.com>
Date: Wed, 26 Nov 2025 16:14:19 +0000
From: Mike Leach <mike.leach@...aro.org>
To: James Clark <james.clark@...aro.org>
Cc: Leo Yan <leo.yan@....com>, Kuan-Wei Chiu <visitorckw@...il.com>, suzuki.poulose@....com, 
	alexander.shishkin@...ux.intel.com, pratikp@...eaurora.org, 
	mathieu.poirier@...aro.org, gregkh@...uxfoundation.org, 
	jserv@...s.ncku.edu.tw, marscheng@...gle.com, ericchancf@...gle.com, 
	milesjiang@...gle.com, nickpan@...gle.com, coresight@...ts.linaro.org, 
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] coresight: etm3x: Fix buffer overwrite in cntr_val_show()

On Wed, 26 Nov 2025 at 15:33, James Clark <james.clark@...aro.org> wrote:
>
>
>
> On 26/11/2025 1:42 pm, Mike Leach wrote:
> > Hi,
> >
> > On Wed, 26 Nov 2025 at 12:31, Leo Yan <leo.yan@....com> wrote:
> >>
> >> On Wed, Nov 26, 2025 at 12:11:05PM +0000, James Clark wrote:
> >>
> >> [...]
> >>
> >>>> This fix can still be applied to older kernels, but seems to me that
> >>>> now might be an appropriate time to consider removing the ETMv3 driver
> >>>> from the mainline kernel?
> >>>
> >>> Yeah, if anyone is using it it would be on an old kernel surely?
> >>
> >> We can confirm this in another way: if I don't miss anything, over the
> >> past several years (since 2017), we have not received any questions or
> >> bug reports based on hands-on practice regarding ETMv3 on the Coresight
> >> or perf mailing lists.
> >>
> >> Thanks,
> >> Leo
> >
> > The key to this is not the questions we are asked, but which platforms
> > are still supported by the linux kernel.
> >
> > The ETMv3 driver supports both ETMv3 and PTM trace (the programming
> > model is the same, even if the trace decode is vastly different).
> >
> > So as long as there are  platforms supported that use either of those,
> > we need to keep the driver in.
> >
> > Mike
> >
>
> We're not running tests though, so if we find out it's fundamentally
> broken somehow it could be another justification to remove it, even if
> the kernel supports the devices. Do you have a board that you can test
> on Mike?
>

Don't have one myself, but I believe the TC2 was used in development,
(that's the A15/A7 32 bit part - not total compute!) which somewhat
conveniently had both etmv3 and ptm trace.



> Maintenance hasn't been zero cost either, even build testing for arm32
> is annoying enough.
>

Pretty much the seem for any of the arm32 drivers I guess.

Until arm32 kernels are no longer supported, not sure it is safe to
drop the etm3 driver as we do not know who out there might be using
it.

Mike




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