Message-ID: <c66deb8f-774e-4981-accf-4f507943e08c@broadcom.com>
Date: Thu, 26 Jun 2025 09:39:36 -0700
From: Florian Fainelli <florian.fainelli@...adcom.com>
To: "Liam R. Howlett" <Liam.Howlett@...cle.com>,
 linux-kernel@...r.kernel.org, Jan Kiszka <jan.kiszka@...mens.com>,
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Subject: Re: [PATCH 00/16] MAINTAINERS: Include GDB scripts under their
 relevant subsystems

On 6/26/25 09:17, Liam R. Howlett wrote:
> * Florian Fainelli <florian.fainelli@...adcom.com> [250625 19:13]:
>> Linux has a number of very useful GDB scripts under scripts/gdb/linux/*
>> that provide OS awareness for debuggers and allows for debugging of a
>> variety of data structures (lists, timers, radix tree, mapletree, etc.)
>> as well as subsystems (clocks, devices, classes, busses, etc.).
>>
>> These scripts are typically maintained in isolation from the subsystem
>> that they parse the data structures and symbols of, which can lead to
>> people playing catch up with fixing bugs or updating the script to work
>> with updates made to the internal APIs/objects etc. Here are some
>> recents examples:
>>
>> https://lore.kernel.org/all/20250601055027.3661480-1-tony.ambardar@gmail.com/
>> https://lore.kernel.org/all/20250619225105.320729-1-florian.fainelli@broadcom.com/
>> https://lore.kernel.org/all/20250625021020.1056930-1-florian.fainelli@broadcom.com/
>>
>> This patch series is intentionally split such that each subsystem
>> maintainer can decide whether to accept the extra
>> review/maintenance/guidance that can be offered when GDB scripts are
>> being updated or added.
> 
> I don't see why you think it was okay to propose this in the way you
> have gone about it.  Looking at the mailing list, you've been around for
> a while.

This should probably have been posted as RFC rather than PATCH, but as I 
indicate in the cover letter this is broken down to allow maintainers 
like yourself to accept/reject

> 
> The file you are telling me about seems to be extremely new and I needed
> to pull akpm/mm-new to discover where it came from.. because you never
> Cc'ed me on the file you are asking me to own.

Yes, that file is very new indeed, and my bad for not copying you on it.

I was not planning on burning an entire day worth of work to transition 
the GDB scripts dumping the interrupt tree away from a radix tree to a 
maple tree. All of which happens with the author of that conversion 
having absolutely no idea that broke anything in the tree because very 
few people know about the Python GDB scripts that Linux has. It is not 
pleasant to be playing catch when it would have take maybe an extra 
couple hours for someone intimately familiar with the maple tree to come 
up with a suitable implementation replacement for mtree_load().

So having done it felt like there is a maintenance void that needs to be 
filled, hence this patch set.

> 
> I'm actually apposed to the filename you used for the script you want me
> to own.

Is there a different filename that you would prefer?

> 
> I consider myself a low-volume email maintainer and I get enough useless
> emails about apparent trivial fixes that end up causing significant
> damage if they are not dealt with.  So I take care not to sign up for
> more time erosion from meaningful forward progress on tasks I hope to
> have high impact.  I suspect you know that, but I don't know you so I
> don't want to assume.

That seems entirely sane and thanks for being explicit about it.

> 
> Is there anything else you might want to share to entice me to maintain
> this file?  Perhaps there's a documentation pointer that shows how
> useful it is and why I should use it?

It can be as simple as spawning a QEMU instance:

qemu-system-x86_64 \
         -s \
         -cpu "max" \
         -smp 4 \
         -kernel ~/dev/linux/arch/x86/boot/bzImage \
         -device pci-bridge,id=pci_bridge1,bus=pci.0,chassis_nr=1 \
         -drive 
file=debian.img,if=none,id=drive-virtio-disk0,format=qcow2 -device 
virtio-blk-pci,scsi=off,drive=drive-virtio-disk0,id=virtio-disk0,bootindex=1 
\
         -nographic \
         -append "root=/dev/vda1 console=ttyS0,115200 mitigations=off" \
         -net nic,model=e1000 -net tap,ifname=tap0

and in another terminal running GDB with:

gdb vmlinux -ex "target remote localhost:1234" -ex "lx-interruptlist"

to obtain a dump of /proc/interrupts which is effectively a replacement 
for iterating over every interrupt descriptor in the system.

> 
> Right now, I have no idea what that file does or how to even check if
> that file works today, so I cannot sign on to maintain it.
> 
> If you want to depend on APIs, this should probably be generated in a
> way that enables updates.  And if that's the case, then why even have a
> file at all and just generate it when needed?  Or, at least, half
> generated and finished by hand?

As it stands today that is not happening, there is zero coordination and 
people who care about GDB scripts just play catch up. But you raise a 
good point, if we are to do that, then we should be able to target 
C/Rust/Python/whatever, that seems like a bigger undertaking and I am 
not clear whether the kernel community as a whole is looking for 
transitioning over to something like this.

> 
> Maybe this is the case but scripts/gdb doesn't have any documentation in
> there, there's no Documentation/scripts or Documentation/gdb either.
> 
> Can you please include more details on the uses of these files?  Failing
> that, perhaps you could point to any documentation?

See the two commands above, those should give you a good environment to 
play with the various GDB scripts which are all prefix with "lx-".

Thanks!
-- 
Florian

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