Re: [PATCH bpf-next v4 09/12] bpf, trace, net: prepare CONFIG_DEBUG_INFO_BTF checks for a tristate

[Nicolas Schier <nsc@kernel.org>]

On Thu, Oct 01, 2026 at 10:52:11PM +0000, Jay Wang wrote:
> The next patch makes CONFIG_DEBUG_INFO_BTF a tristate.  With =m, Kconfig
> defines CONFIG_DEBUG_INFO_BTF_MODULE instead of CONFIG_DEBUG_INFO_BTF,
> so every check that must hold for both =y and =m has to be written for
> it:
> 
>  - #ifdef CONFIG_DEBUG_INFO_BTF becomes #if IS_ENABLED(...) where the
>    generated BTF and its id tables must be the same for =y and =m: the
>    .BTF_ids tables (btf_ids.h), the BTF type tags (compiler_types.h), and
>    the tracepoint and syscall BTF ids (trace_events.h, trace_syscalls.c).
>    Leaving them would silently produce empty id sets with =m.
> 
>  - obj-$(CONFIG_DEBUG_INFO_BTF) and include-$(CONFIG_DEBUG_INFO_BTF)
>    become $(subst m,y,...) where the object is built into the kernel
>    regardless: sysfs_btf.o, the netfilter and xfrm kfunc objects, and
>    scripts/Makefile.btf.  Otherwise =m would try to build them as
>    modules (xfrm_state_bpf.o fails modpost for lack of MODULE_LICENSE)
>    or skip the BTF generation flags.
> 
>  - "depends on !DEBUG_INFO_BTF" becomes "depends on DEBUG_INFO_BTF=n"
>    for RUST and GENDWARFKSYMS: with =m the BTF is generated as with =y,
>    so the pahole restrictions they express still apply, but !m is m,
>    which a bool option takes as y.
> 
> No functional change: CONFIG_DEBUG_INFO_BTF is still a bool, for which
> IS_ENABLED() and #ifdef agree, $(subst m,y,y) is y and "=n" is "!".
> 
> Signed-off-by: Jay Wang <wanjay@amazon.com>
> ---
>  Makefile                       | 3 ++-
>  include/linux/btf_ids.h        | 2 +-
>  include/linux/compiler_types.h | 2 +-
>  include/trace/trace_events.h   | 2 +-
>  init/Kconfig                   | 2 +-
>  kernel/bpf/Makefile            | 2 +-
>  kernel/module/Kconfig          | 2 +-
>  kernel/trace/trace_syscalls.c  | 6 +++---
>  net/netfilter/Makefile         | 6 +++---
>  net/xfrm/Makefile              | 4 ++--
>  10 files changed, 16 insertions(+), 15 deletions(-)
> 
> diff --git a/Makefile b/Makefile
> index 751a08643bf8..f561516e1735 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -1208,7 +1208,8 @@ endif
>  # include additional Makefiles when needed
>  include-y			:= scripts/Makefile.warn
>  include-$(CONFIG_DEBUG_INFO)	+= scripts/Makefile.debug
> -include-$(CONFIG_DEBUG_INFO_BTF)+= scripts/Makefile.btf
> +# CONFIG_DEBUG_INFO_BTF is a tristate; BTF is generated for both y and m
> +include-$(subst m,y,$(CONFIG_DEBUG_INFO_BTF)) += scripts/Makefile.btf

Please drop the comment and use the shorter 'm' to 'y' conversion:

include-$(CONFIG_DEBUG_INFO_BTF:m=y)	+= scripts/Makefile.btf

and possibly also for kernel/bpf/Makefile and net/netfilter/Makefile.

Thanks


-- 
Nicolas