[PATCH bpf] bpf: make DEBUG_INFO_BTF_MODULES selectable independently

[Stanislav Fomichev <sdf@google.com>]

We're having an issue where we have a recent clang that seems
to generate kind_flag for enums (aka, adding signed/unsigned).
Trying to install a module on a kernel that doesn't have commit
6089fb325cf7 ("bpf: Add btf enum64 support") returns the following:

[    3.176954] BPF:Invalid btf_info kind_flag

The enum that it complains about doesn't seem to have anything special
except having a sign:

[1721] ENUM 'perf_event_state' encoding=SIGNED size=4 vlen=6
        'PERF_EVENT_STATE_DEAD' val=-4
        'PERF_EVENT_STATE_EXIT' val=-3
        'PERF_EVENT_STATE_ERROR' val=-2
        'PERF_EVENT_STATE_OFF' val=-1
        'PERF_EVENT_STATE_INACTIVE' val=0
        'PERF_EVENT_STATE_ACTIVE' val=1

We are not currently using CONFIG_DEBUG_INFO_BTF_MODULES and
don't plan to use module BTF, so it's preferable to be able
to explicits disable it in the kernel config. Unfortunately,
because that kconfig option doesn't have a name, it's not
possible to flip it independently from CONFIG_DEBUG_INFO_BTF.
Let's add a name to make sure module BTF is user-controllable.

(Not sure, but maybe the right fix is to also have a stable patch
 to relax that "Invalid btf_info kind_flag" check?)

Fixes: 5f9ae91f7c0d ("kbuild: Build kernel module BTFs if BTF is enabled and pahole supports it")
Signed-off-by: Stanislav Fomichev <sdf@google.com>
---
 lib/Kconfig.debug | 1 +
 1 file changed, 1 insertion(+)

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index c77fe36bb3d8..6336a697c9f5 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -326,6 +326,7 @@ config PAHOLE_HAS_SPLIT_BTF
 	def_bool $(success, test `$(PAHOLE) --version | sed -E 's/v([0-9]+)\.([0-9]+)/\1\2/'` -ge "119")
 
 config DEBUG_INFO_BTF_MODULES
+	bool "Generate BTF module typeinfo"
 	def_bool y
 	depends on DEBUG_INFO_BTF && MODULES && PAHOLE_HAS_SPLIT_BTF
 	help
-- 
2.38.0.rc1.362.ged0d419d3c-goog