Re: [PATCH v2] bpf/scripts: Generate GCC compatible helpers

From: Yonghong Song
Date: Mon Jul 11 2022 - 19:36:22 EST

On 7/6/22 10:28 AM, James Hilliard wrote:
The current bpf_helper_defs.h helpers are llvm specific and don't work
correctly with gcc.

GCC appears to required kernel helper funcs to have the following
attribute set: __attribute__((kernel_helper(NUM)))

Generate gcc compatible headers based on the format in bpf-helpers.h.

This adds conditional blocks for GCC while leaving clang codepaths
unchanged, for example:
#if __GNUC__ && !__clang__
void *bpf_map_lookup_elem(void *map, const void *key) __attribute__((kernel_helper(1)));
static void *(*bpf_map_lookup_elem)(void *map, const void *key) = (void *) 1;

It does look like that gcc kernel_helper attribute is better than
'(void *) 1' style. The original clang uses '(void *) 1' style is
just for simplicity.

Do you mind to help implement similar attribute in clang so we
don't need "#if" here?

#if __GNUC__ && !__clang__
long bpf_map_update_elem(void *map, const void *key, const void *value, __u64 flags) __attribute__((kernel_helper(2)));
static long (*bpf_map_update_elem)(void *map, const void *key, const void *value, __u64 flags) = (void *) 2;


This fixes the following build error:
error: indirect call in function, which are not supported by eBPF

Signed-off-by: James Hilliard <james.hilliard1@xxxxxxxxx>
Changes v1 -> v2:
- more details in commit log
scripts/ | 43 ++++++++++++++++++++++++++-----------------
1 file changed, 26 insertions(+), 17 deletions(-)