Re: [PATCH] tracing: fprobe: Remove __packed from generic __fprobe_header

[Markus Schneider-Pargmann]

Hi Masami,

On Wed Jun 10, 2026 at 10:17 AM CEST, Masami Hiramatsu wrote:
> Hi Markus,
>
> Thanks for ping me.
>
> On Tue, 28 Apr 2026 10:30:29 +0200
> "Markus Schneider-Pargmann (The Capable Hub)" <msp@xxxxxxxxxxxx> wrote:
>
>> fp pointer and unsigned long have the same size on all relevant
>> architectures that build Linux. Furthermore this struct is only used in
>> architectures that do not set ARCH_DEFINE_ENCODE_FPROBE_HEADER which is
>> set only for 64bit architectures (apart from LoongArch).
>> 
>> Both fields are aligned on these architectures so the struct with
>> __packed and without it are the same.
>> 
>> Remove the __packed as it is unnecessary.
>> 
>> Fixes: 4346ba160409 ("fprobe: Rewrite fprobe on function-graph tracer")
>
> NOTE: This is not a Fix, but just cleanup or minor update. Or, you have
> any problem with this __packed attribute?

Thanks, yes it is not fixing a bug, I can remove this.

>
> Unless there is no problem (or any concern), I would like to keep this
> as it is.

There is currently no problem with __packed in the upstream kernel. I
just thought this would be a good cleanup to remove the unnecessary
attribute. I am working on CHERI architectures where pointers have
capabilities. __packed breaks these capability tags and therefore
doesn't work on CHERI. When looking into why this struct has a __packed
attribute I didn't see a reason, so I thought this would be a good patch
for upstream as well even though CHERI is not yet relevant for upstream
linux.

Best
Markus

Attachment: signature.asc
Description: PGP signature