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bpftool: Support dumping kfunc prototypes from BTF

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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@dxuuu.xyz>
Link: https://lore.kernel.org/r/bf6c08f9263c4bd9d10a717de95199d766a13f61.1718207789.git.dxu@dxuuu.xyz
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Daniel Xu 2024-06-12 09:58:36 -06:00 committed by Alexei Starovoitov
parent c567cba345
commit 770abbb5a2
1 changed files with 55 additions and 0 deletions
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55
tools/bpf/bpftool/btf.c
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@ -20,6 +20,8 @@
#include "json_writer.h" #include "json_writer.h"
#include "main.h" #include "main.h"
#define KFUNC_DECL_TAG "bpf_kfunc"
static const char * const btf_kind_str[NR_BTF_KINDS] = { static const char * const btf_kind_str[NR_BTF_KINDS] = {
[BTF_KIND_UNKN] = "UNKNOWN", [BTF_KIND_UNKN] = "UNKNOWN",
[BTF_KIND_INT] = "INT", [BTF_KIND_INT] = "INT",
@ -461,6 +463,49 @@ static int dump_btf_raw(const struct btf *btf,
return 0; 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");
printf("#ifndef BPF_NO_KFUNC_PROTOTYPES\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("#endif\n\n");
return 0;
}
static void __printf(2, 0) btf_dump_printf(void *ctx, static void __printf(2, 0) btf_dump_printf(void *ctx,
const char *fmt, va_list args) const char *fmt, va_list args)
{ {
@ -596,6 +641,12 @@ static int dump_btf_c(const struct btf *btf,
printf("#ifndef BPF_NO_PRESERVE_ACCESS_INDEX\n"); printf("#ifndef BPF_NO_PRESERVE_ACCESS_INDEX\n");
printf("#pragma clang attribute push (__attribute__((preserve_access_index)), apply_to = record)\n"); printf("#pragma clang attribute push (__attribute__((preserve_access_index)), apply_to = record)\n");
printf("#endif\n\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) { if (root_type_cnt) {
for (i = 0; i < root_type_cnt; i++) { for (i = 0; i < root_type_cnt; i++) {
@ -615,6 +666,10 @@ static int dump_btf_c(const struct btf *btf,
if (err) if (err)
goto done; goto done;
} }
err = dump_btf_kfuncs(d, btf);
if (err)
goto done;
} }
printf("#ifndef BPF_NO_PRESERVE_ACCESS_INDEX\n"); printf("#ifndef BPF_NO_PRESERVE_ACCESS_INDEX\n");