linux-kernel - Re: [PATCH v2] drivers: gpu: drm: msm: registers: improve reproducibility

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Message-ID: <CACSVV02YrpYrvbFxKc808a=GjdxVjO=FjRG9gs_6qe5W-v=a9g@mail.gmail.com>
Date: Mon, 8 Sep 2025 07:19:41 -0700
From: Rob Clark <rob.clark@....qualcomm.com>
To: Ryan Eatmon <reatmon@...com>
Cc: Rob Clark <robdclark@...il.com>,
        Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>,
        Viswanath Kraleti <viswanath.kraleti@....qualcomm.com>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>, Sean Paul <sean@...rly.run>,
        Marijn Suijten <marijn.suijten@...ainline.org>,
        David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
        linux-arm-msm@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        freedreno@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Bruce Ashfield <bruce.ashfield@...il.com>
Subject: Re: [PATCH v2] drivers: gpu: drm: msm: registers: improve reproducibility

On Mon, Sep 8, 2025 at 6:39 AM Ryan Eatmon <reatmon@...com> wrote:
>
>
>
> On 9/6/2025 6:24 PM, Rob Clark wrote:
> > On Sat, May 24, 2025 at 10:15 AM Dmitry Baryshkov
> > <dmitry.baryshkov@....qualcomm.com> wrote:
> >>
> >> On Sat, May 24, 2025 at 09:25:37PM +0530, Viswanath Kraleti wrote:
> >>> From: Ryan Eatmon <reatmon@...com>
> >>>
> >>> The files generated by gen_header.py capture the source path to the
> >>> input files and the date.  While that can be informative, it varies
> >>> based on where and when the kernel was built as the full path is
> >>> captured.
> >>>
> >>> Since all of the files that this tool is run on is under the drivers
> >>> directory, this modifies the application to strip all of the path before
> >>> drivers.  Additionally it prints <stripped> instead of the date.
> >>>
> >>> Signed-off-by: Ryan Eatmon <reatmon@...com>
> >>> Signed-off-by: Bruce Ashfield <bruce.ashfield@...il.com>
> >>> Signed-off-by: Viswanath Kraleti <viswanath.kraleti@....qualcomm.com>
> >>> ---
> >>> The files generated by gen_header.py include the source path to the
> >>> input files and the build date. While this information can be useful,
> >>> it inadvertently exposes build system configuration details in the
> >>> binaries. This hinders binary reproducibility, as the output will
> >>> vary if the build environment changes.
> >>>
> >>> This change was originally submitted to the linux-yocto-dev kernel [1]
> >>> to address binary reproducibility QA errors. However, the fix is generic
> >>> enough to be applicable to the mainline kernel and would benefit other
> >>> distributions as well. So proposing it here for broader inclusion.
> >>>
> >>> [1] https://git.yoctoproject.org/linux-yocto-dev/commit/?id=f36faf0f9f8d8f5b4c43a68e5c6bd83a62253140
> >>> ---
> >>> Changes in v2:
> >>> - Corrected author id
> >>> - Link to v1: https://lore.kernel.org/r/20250523-binrep-v1-1-c3a446518847@oss.qualcomm.com
> >>> ---
> >>>   drivers/gpu/drm/msm/registers/gen_header.py | 8 +++++---
> >>>   1 file changed, 5 insertions(+), 3 deletions(-)
> >>>
> >>
> >> Acked-by: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
> >>
> >> Rob, WDYT?
> >
> > I'm revisiting this one, in the context of trying to re-sync
> > gen_header.py with mesa.. but it is only changing the contents of
> > comments, so it's not quite clear to me how this ends up mattering for
> > binary reproducibility.
>
> The reason it matters is that for Yocto, the generated header file is
> identified as a file that needs to be installed into the sysroot.  All
> files going into the sysroot are checked to make sure they do not
> contain dates and/or paths to the build directory contained within.
> Since this is a generated header file that is included in the sysroot we
> needed to strip out the path and date.
>
> The idea for the reproducible builds are that the same files on a
> different a machine at a different time should produce 100% identical
> files.  Including paths and dates violates that tenet.
>
> Hope that helps explain why we needed this.  So long as the
> gen_header.py is being called to generate header files then we need to
> maintain the reproducible aspect.
>

My plan is (was?) to just replace the entire comment header with simply:

  /* Autogenerated file, DO NOT EDIT manually! */

That said, I'm not entirely sure why these files should get installed
into the sysroot?  I'm not super hands-on familiar with Yocto, so
maybe there is a good reason.. but if there is, maybe the plan to
remove the license/etc from the comment header isn't such a good idea
after all?

BR,
-R

>
> > That said, since the generated files are no longer checked in to mesa
> > or the kernel, we could probably just drop all of this if it mattered.
> >
> > BR,
> > -R
>
> --
> Ryan Eatmon                reatmon@...com
> -----------------------------------------
> Texas Instruments, Inc.  -  LCPD  -  MGTS
>
>