Re: [PATCH v2] Fix build failure due to btf on Linux < 6.0

[Giulio Benetti <giulio.benetti@benettiengineering.com>]

Hi Steve,

On 12/03/2026 21:36, Giulio Benetti wrote:
> 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) <rostedt@goodmis.org>
> Co-authored-by: Giulio Benetti <giulio.benetti@benettiengineering.com>
> Signed-off-by: Giulio Benetti <giulio.benetti@benettiengineering.com>
> ---
> V1->V2:
> * fixed meson check and all bft C source
> ---
>   Makefile        | 28 +++++++++++++++++++++-------
>   src/meson.build | 12 ++++++++++++
>   src/trace-btf.c | 31 +++++++++++++++++++++++++++++--
>   3 files changed, 62 insertions(+), 9 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; }

This ^^^ check is not enough. I try to think about something better

Best regards
Giulio

> +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..2432dd8 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 not 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..52e933c 100644
> --- a/src/trace-btf.c
> +++ b/src/trace-btf.c
> @@ -8,12 +8,13 @@
>   #include <stdlib.h>
>   #include <stdbool.h>
>   
> -#include <linux/btf.h>
> -
>   #include "event-parse.h"
>   #include "event-utils.h"
>   #include "event-parse-local.h"
>   
> +#ifndef NO_BTF
> +#include <linux/btf.h>
> +
>   struct btf_header;
>   struct btf_type;
>   
> @@ -210,17 +211,24 @@ static int load_types(struct tep_btf *btf)
>   	qsort_r(btf->funcs, btf->nr_funcs, sizeof(btf->funcs[0]), cmp_funcs, btf);
>   	return 0;
>   }
> +#endif
>   
>   __hidden void btf_free(struct tep_btf *btf)
>   {
> +#ifdef NO_BTF
> +	tep_warning("BTF not supported.\n");
> +	return;
> +#else
>   	if (!btf)
>   		return;
>   
>   	free(btf->types);
>   	free(btf->funcs);
>   	free(btf->raw_data);
> +#endif
>   }
>   
> +#ifndef NO_BTF
>   static struct tep_btf *btf_init(void *raw_data, size_t data_size)
>   {
>   	struct tep_btf *btf;
> @@ -271,6 +279,7 @@ static struct tep_btf *btf_init(void *raw_data, size_t data_size)
>   	btf_free(btf);
>   	return NULL;
>   }
> +#endif
>   
>   /**
>    * tep_load_btf - Load BTF information into a tep handle
> @@ -285,6 +294,10 @@ static struct tep_btf *btf_init(void *raw_data, size_t data_size)
>    */
>   int tep_load_btf(struct tep_handle *tep, void *raw_data, size_t data_size)
>   {
> +#ifdef NO_BTF
> +	tep_warning("BTF not supported.\n");
> +	return -1;
> +#else
>   	/* If btf was already loaded, free it */
>   	btf_free(tep->btf);
>   
> @@ -292,8 +305,10 @@ int tep_load_btf(struct tep_handle *tep, void *raw_data, size_t data_size)
>   	if (!tep->btf)
>   		return -1;
>   	return 0;
> +#endif
>   }
>   
> +#ifndef NO_BTF
>   static struct btf_type *btf_get_type(struct tep_btf *btf, int id)
>   {
>   	if (!id || id > btf->nr_types)
> @@ -457,6 +472,7 @@ static int init_btf_func(struct tep_btf *btf, struct trace_seq *s,
>   
>   	return 0;
>   }
> +#endif
>   
>   /**
>    * tep_btf_list_args - List the arguments (type and name) for a function
> @@ -471,6 +487,10 @@ 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
> +	tep_warning("BTF not supported.\n");
> +	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 +540,7 @@ 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 +564,11 @@ 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 +672,5 @@ int tep_btf_print_args(struct tep_handle *tep, struct trace_seq *s, void *args,
>   		}
>   	}
>   	return 0;
> +#endif
>   }