[PATCH] Fix build failure due to btf on Linux < 6.0

With commit:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=6089fb325cf737eeb2c4d236c94697112ca860da
enum BTF_KIND_ENUM64 has been firstly introduced and this is the latest
BTF_KIND_* enumaration to be added to libtraceevent. So let's check
in runtime, both in Makefile and meson, if BTF_KIND_ENUM64 does exist.
If it's not there let's disable btf support.

Signed-off-by: Steven Rostedt (Google) <[email protected]>
Co-authored-by: Giulio Benetti <[email protected]>
Signed-off-by: Giulio Benetti <[email protected]>
---
 Makefile        | 28 +++++++++++++++++++++-------
 src/meson.build | 12 ++++++++++++
 src/trace-btf.c | 10 ++++++++++
 3 files changed, 43 insertions(+), 7 deletions(-)

diff --git a/Makefile b/Makefile
index e1a10a0..bd88a98 100644
--- a/Makefile
+++ b/Makefile
@@ -27,6 +27,13 @@ $(call allow-override,PKG_CONFIG,pkg-config)
 $(call allow-override,LD_SO_CONF_PATH,/etc/ld.so.conf.d/)
 $(call allow-override,LDCONFIG,ldconfig)
 
+# Set compile option CFLAGS
+ifdef EXTRA_CFLAGS
+  CFLAGS ?= $(EXTRA_CFLAGS)
+else
+  CFLAGS ?= -g -Wall
+endif
+
 EXT = -std=gnu99
 INSTALL = install
 
@@ -37,6 +44,20 @@ INSTALL = install
 DESTDIR ?=
 DESTDIR_SQ = '$(subst ','\'',$(DESTDIR))'
 
+test-build = $(if $(shell sh -c 'echo "$(1)" | tee /tmp/t.c| \
+	$(CC) -o /dev/null -x c - > /dev/null 2>&1 && echo y'), $2)
+
+define BTF_LATEST_SOURCE
+#include <linux/btf.h>
+int main(void) { return BTF_KIND_ENUM64; }
+endef
+
+BTF_OK := $(call test-build,$(BTF_LATEST_SOURCE),y)
+
+ifneq ($(strip $(BTF_OK)), y)
+CFLAGS += -DNO_BTF
+endif
+
 LP64 := $(shell echo __LP64__ | ${CC} ${CFLAGS} -E -x c - | tail -n 1)
 ifeq ($(LP64), 1)
   libdir_relative_temp = lib64
@@ -123,13 +144,6 @@ INCLUDES = -I. -I $(srctree)/include -I $(EP_HEADERS_DIR) $(CONFIG_INCLUDES)
 
 export LIBTRACEEVENT_STATIC LIBTRACEEVENT_SHARED EP_HEADERS_DIR
 
-# Set compile option CFLAGS
-ifdef EXTRA_CFLAGS
-  CFLAGS := $(EXTRA_CFLAGS)
-else
-  CFLAGS := -g -Wall
-endif
-
 LIBS ?= -ldl
 export LIBS
 
diff --git a/src/meson.build b/src/meson.build
index 3a7a082..23b43ff 100644
--- a/src/meson.build
+++ b/src/meson.build
@@ -17,6 +17,18 @@ sources= [
 cc = meson.get_compiler('c')
 dl_dep = cc.find_library('dl')
 
+btf_enum64_test_code = '''
+#include <linux/btf.h>
+int main(void) {
+    int x = BTF_KIND_ENUM64;
+    return 0;
+}
+'''
+
+if cc.compiles(btf_enum64_test_code, name : 'BTF_KIND_ENUM64 check')
+    add_project_arguments('-DNO_BTF', language : 'c')
+endif
+
 libtraceevent = library(
     'traceevent',
     sources,
diff --git a/src/trace-btf.c b/src/trace-btf.c
index 859b086..4e3a853 100644
--- a/src/trace-btf.c
+++ b/src/trace-btf.c
@@ -471,6 +471,9 @@ static int init_btf_func(struct tep_btf *btf, struct trace_seq *s,
  */
 int tep_btf_list_args(struct tep_handle *tep, struct trace_seq *s, const char *func)
 {
+#ifdef NO_BTF
+	return -1;
+#else
 	struct tep_btf *btf = tep->btf;
 	struct btf_type *type = tep_btf_find_func(btf, func);
 	struct btf_param *param;
@@ -520,6 +523,7 @@ int tep_btf_list_args(struct tep_handle *tep, struct trace_seq *s, const char *f
 			trace_seq_printf(s, "%s", param_name);
 	}
 	return p;
+#endif
 }
 
 /**
@@ -543,6 +547,11 @@ int tep_btf_list_args(struct tep_handle *tep, struct trace_seq *s, const char *f
 int tep_btf_print_args(struct tep_handle *tep, struct trace_seq *s, void *args,
 		       int nmem, int size, const char *func)
 {
+#ifdef NO_BTF
+	tep_warning("BTF not supported. Args:\n
+		    args: %08x, nmem: %d, size: %d, func: %08x\n");
+	return -1;
+#else
 	struct tep_btf *btf = tep->btf;
 	struct btf_type *type = tep_btf_find_func(btf, func);
 	struct btf_param *param;
@@ -646,4 +655,5 @@ int tep_btf_print_args(struct tep_handle *tep, struct trace_seq *s, void *args,
 		}
 	}
 	return 0;
+#endif
 }
-- 
2.47.3