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

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 <redacted>
---
 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