On Thu, 09 Jul 2026 14:06:32 +0200 "Markus Schneider-Pargmann" <[email protected]> wrote:
> Hi Masami, > > On Mon Jun 22, 2026 at 6:56 AM CEST, Masami Hiramatsu wrote: > > On Wed, 10 Jun 2026 11:20:24 +0200 > > "Markus Schneider-Pargmann" <[email protected]> wrote: > > > >> 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)" <[email protected]> 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. > > > > Hi Markus, > > > > Ah, OK. CHERI makes pointers to non-long value. Are you sure > > removing __packed makes fprobe working with CHERI? If so, > > please describe it. Then I can pick it. > > Sorry for the late response. > > No, this patch alone doesn't make fprobe work with CHERI. __packed is > problematic for CHERI because it sets the alignment to 1 which forces > the compiler to do unaligned access operations even if the > struct/pointer is aligned. Unaligned operations do not keep the CHERI > capabilities. Without __packed the compiler knows everything is aligned > and can use aligned operations and keep the CHERI capabilities. CHERI > hardware does not support unaligned pointer capability access. > > On its own it doesn't help CHERI, there are more patches that are more > CHERI specific that are needed for fprobe to work on CHERI. I just > thought it would be a great standalone patch for upstream. OK, anyway, I would like to pick your patch but without fixes tag. It may make no differences, so should be treated as a cleanup patch. Let me pick it to probes/for-next. Thank you, > > Best > Markus -- Masami Hiramatsu (Google) <[email protected]>
