On Mon, May 13, 2024 at 12:38:59PM GMT, Daniel Xu wrote:
> This patch enables dumping kfunc prototypes from bpftool. This is useful
> b/c with this patch, end users will no longer have to manually define
> kfunc prototypes. For the kernel tree, this also means we can optionally
> drop kfunc prototypes from:
>
> tools/testing/selftests/bpf/bpf_kfuncs.h
> tools/testing/selftests/bpf/bpf_experimental.h
>
> Example usage:
>
> $ make PAHOLE=/home/dxu/dev/pahole/build/pahole -j30 vmlinux
>
> $ ./tools/bpf/bpftool/bpftool btf dump file ./vmlinux format c | rg "__ksym;" | head -3
> extern void cgroup_rstat_updated(struct cgroup *cgrp, int cpu) __weak __ksym;
> extern void cgroup_rstat_flush(struct cgroup *cgrp) __weak __ksym;
> extern struct bpf_key *bpf_lookup_user_key(u32 serial, u64 flags) __weak __ksym;
>
> Signed-off-by: Daniel Xu <dxu@xxxxxxxxx>
> ---
> tools/bpf/bpftool/btf.c | 54 +++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 54 insertions(+)
>
> diff --git a/tools/bpf/bpftool/btf.c b/tools/bpf/bpftool/btf.c
> index 91fcb75babe3..884af6589f0d 100644
> --- a/tools/bpf/bpftool/btf.c
> +++ b/tools/bpf/bpftool/btf.c
> @@ -20,6 +20,8 @@
> #include "json_writer.h"
> #include "main.h"
>
> +#define KFUNC_DECL_TAG "bpf_kfunc"
> +
> static const char * const btf_kind_str[NR_BTF_KINDS] = {
> [BTF_KIND_UNKN] = "UNKNOWN",
> [BTF_KIND_INT] = "INT",
> @@ -454,6 +456,48 @@ static int dump_btf_raw(const struct btf *btf,
> return 0;
> }
>
> +static int dump_btf_kfuncs(struct btf_dump *d, const struct btf *btf)
> +{
> + LIBBPF_OPTS(btf_dump_emit_type_decl_opts, opts);
> + int cnt = btf__type_cnt(btf);
> + int i;
> +
> + printf("\n/* BPF kfuncs */\n");
> +
> + for (i = 1; i < cnt; i++) {
> + const struct btf_type *t = btf__type_by_id(btf, i);
> + const char *name;
> + int err;
> +
> + if (!btf_is_decl_tag(t))
> + continue;
> +
> + if (btf_decl_tag(t)->component_idx != -1)
> + continue;
> +
> + name = btf__name_by_offset(btf, t->name_off);
> + if (strncmp(name, KFUNC_DECL_TAG, sizeof(KFUNC_DECL_TAG)))
> + continue;
> +
> + t = btf__type_by_id(btf, t->type);
> + if (!btf_is_func(t))
> + continue;
> +
> + printf("extern ");
> +
> + opts.field_name = btf__name_by_offset(btf, t->name_off);
> + err = btf_dump__emit_type_decl(d, t->type, &opts);
> + if (err)
> + return err;
> +
> + printf(" __weak __ksym;\n");
> + }
> +
> + printf("\n");
> +
> + return 0;
> +}
> +
> static void __printf(2, 0) btf_dump_printf(void *ctx,
> const char *fmt, va_list args)
> {
> @@ -476,6 +520,12 @@ static int dump_btf_c(const struct btf *btf,
> printf("#ifndef BPF_NO_PRESERVE_ACCESS_INDEX\n");
> printf("#pragma clang attribute push (__attribute__((preserve_access_index)), apply_to = record)\n");
> printf("#endif\n\n");
> + printf("#ifndef __ksym\n");
> + printf("#define __ksym __attribute__((section(\".ksyms\")))\n");
> + printf("#endif\n\n");
> + printf("#ifndef __weak\n");
> + printf("#define __weak __attribute__((weak))\n");
> + printf("#endif\n\n");
>
> if (root_type_cnt) {
> for (i = 0; i < root_type_cnt; i++) {
> @@ -491,6 +541,10 @@ static int dump_btf_c(const struct btf *btf,
> if (err)
> goto done;
> }
> +
> + err = dump_btf_kfuncs(d, btf);
> + if (err)
> + goto done;
> }
>
> printf("#ifndef BPF_NO_PRESERVE_ACCESS_INDEX\n");
> --
> 2.44.0
>
>
Oh, looks like selftests fail to build. I will fix that for v4.
