Re: [PATCH RFC v3 03/13] sysctl, mod_devicetable: add macro MODULE_SYSCTL_TABLE

On 2026-08-23 19:12, Uwe Kleine-König wrote:

Hello Mauricio,

On Sat, Aug 22, 2026 at 01:57:24PM -0300, Mauricio Faria de Oliveira wrote:

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On 2026-08-22 10:41, Uwe Kleine-König wrote:

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On Wed, Aug 19, 2026 at 03:16:16PM -0300, Mauricio Faria de Oliveira wrote:

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The MODULE_SYSCTL_TABLE macro emits a struct module_sysctl_table variable
with pointers to a sysctl table's path and entries, and table/entry sizes.

That new struct doesn't seem to contain any pointer?

The struct module_sysctl_table fields .path and .table are pointers,
although with kernel_ulong_t type so that the same 32/64-bit size is
used in file2alias.c based on KERNEL_ELFCLASS (and not on the host,
which might differ with CROSS_COMPILE).

Cross compilation isn't an issue for the already existing device id
structures; many of them also contain pointers.
(While modpost doesn't use the pointers, the size of the structures must
be known to correctly interpret the arrays.)

Indeed. I missed some device_id structures with pointers, and that
devicetable-offsets.c is cross-compiled to generate
devicetable-offsets.h for file2alias.c to use offsets and sizes of the
target architecture.

I'll change .path and .table to pointers in the next version.

Also sizeof(long) differs between architectures and I can compile for
arm(32) just fine on amd64.

Additionally there is hardware out there that has sizeof(void *) = 16
but sizeof(long) = 8. Up until recently I worked on mainlining that (and
it has business reasons only I stopped, so I guess and hope I will
continue at some point in the future). See
https://lwn.net/Articles/1037974/ for some details if you're interested.

Cool.

I would be great if your series didn't introduce a new obstacle for
that.

Absolutely. I'll be happy to adjust the series and testing for that.

Could you please confirm one should just follow [1], which uses [2] to
build the LLVM toolchain, and use it to build the kernel [3]?

[1] https://github.com/cheri-linux#building-and-running
[2] https://github.com/cheri-linux/buildroot
[3] https://github.com/CHERI-Alliance/linux/tree/codasip-cheri-riscv-7.1

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That symbol will be handled by file2alias.c (modpost) with the changes in
mod_devicetable.h and devicetable-offsets.c.

The option macros MODULE_SYSCTL_TABLE_{DISABLE,UNIQUE_ID} can be used on
a per-file basis to disable the macro and change the symbol name pattern.

Signed-off-by: Mauricio Faria de Oliveira <redacted>
---
 include/linux/mod_devicetable.h   |  7 +++++++
 include/linux/sysctl.h            | 42 +++++++++++++++++++++++++++++++++++++++
 scripts/mod/devicetable-offsets.c |  6 ++++++
 3 files changed, 55 insertions(+)

Please put the new struct in a separate header. Apart from not being
about a device table, I'm currently work on removing
<linux/mod_devicetable.h>. See commit
ad428f5811bd7fb3d91fa002174de533f9da94d7 for more details.

Sure; I looked at that earlier (thanks for the instructive commit
message, by the way) and found the new struct to be similar to "struct
cpu_feature isn't really a device_id struct" (not moved), but apparently
missed the trailing "fow now", which is clearer now. Fixed for v4.

Yeah, I didn't move that because it was an outlier in the header as it's
not a device id. IMHO it should go to something like
include/linux/cpu_feature.h.

Ack.

cheers,

Best regards
Uwe

-- 
Mauricio