Re: [RFC bpf-next 12/15] kbuild, module, bpf: Support CONFIG_DEBUG_INFO_BTF_EXTRA=m

[Alan Maguire <alan.maguire@oracle.com>]

On 16/10/2025 19:37, Andrii Nakryiko wrote:
> On Wed, Oct 8, 2025 at 10:36 AM Alan Maguire <alan.maguire@oracle.com> wrote:
>>
>> Allow module-based delivery of potentially large vmlinux .BTF.extra section;
>> section; also support visibility of BTF data in kernel, modules in
>> /sys/kernel/btf_extra.
>>
> 
> nit: whatever naming we pick, I'd keep all the BTF exposed under the
> same /sys/kernel/btf/ directory. And then use suffixes to denote extra
> subsets of BTF. E.g., vmlinux is base vmlinux BTF, vmlinux.funcs (or
> whatever we will agree on) will be split BTF on top of vmlinux BTF
> with all this function information. Same for kernel modules: <module>
> for "base module BTF" (which is itself split on top of vmlinux, of
> course), and <module>.funcs for this extra func info stuff,
> (multi-)split on top of <module> BTF itself.
> 

I went back and forth on this; my only hesitation in adding to
/sys/kernel/btf was that I was concerned existing tools might make
assumptions about its contents; i.e.

- vmlinux is kernel BTF
- everything else is module BTF relative to base BTF

If we're not too worried about that we can put it in the same directory
with the "." connoting split BTF relative to the prefix

/sys/kernel/btf/[vmlinux|module].func_info

Don't think a "." is valid in a module name, so there should never be
name clashes.

For completeness another possibility is

/sys/kernel/btf/func.info/[vmlinux|module_name]

However I'm happy to adjust to whateer seems most intuitive. Thanks!

>> Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
>> ---
>>  include/linux/bpf.h       |   1 +
>>  include/linux/btf.h       |   2 +
>>  include/linux/module.h    |   4 ++
>>  kernel/bpf/Makefile       |   1 +
>>  kernel/bpf/btf.c          | 114 +++++++++++++++++++++++++++-----------
>>  kernel/bpf/btf_extra.c    |  25 +++++++++
>>  kernel/bpf/sysfs_btf.c    |  21 ++++++-
>>  kernel/module/main.c      |   4 ++
>>  lib/Kconfig.debug         |   2 +-
>>  scripts/Makefile.btf      |   3 +-
>>  scripts/Makefile.modfinal |   5 ++
>>  scripts/link-vmlinux.sh   |   6 ++
>>  12 files changed, 154 insertions(+), 34 deletions(-)
>>  create mode 100644 kernel/bpf/btf_extra.c
>>
> 
> [...]