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Message-ID: <9b8ebd13300e28bd92a2e6de4fb04f85c1b6ce7c.1707080349.git.dxu@dxuuu.xyz>
Date: Sun, 4 Feb 2024 14:06:35 -0700
From: Daniel Xu <dxu@...uu.xyz>
To: quentin@...valent.com,
daniel@...earbox.net,
ast@...nel.org,
andrii@...nel.org,
olsajiri@...il.com,
alan.maguire@...cle.com
Cc: martin.lau@...ux.dev,
eddyz87@...il.com,
song@...nel.org,
yonghong.song@...ux.dev,
john.fastabend@...il.com,
kpsingh@...nel.org,
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jolsa@...nel.org,
bpf@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: [PATCH bpf-next v2 2/2] bpftool: Support dumping kfunc prototypes from BTF
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 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;
Note that this patch is only effective after the enabling pahole [0]
change is merged and the resulting feature enabled with
--btf_features=decl_tag_kfuncs.
[0]: https://lore.kernel.org/bpf/cover.1707071969.git.dxu@dxuuu.xyz/
Signed-off-by: Daniel Xu <dxu@...uu.xyz>
---
tools/bpf/bpftool/btf.c | 45 +++++++++++++++++++++++++++++++++++++++++
1 file changed, 45 insertions(+)
diff --git a/tools/bpf/bpftool/btf.c b/tools/bpf/bpftool/btf.c
index 91fcb75babe3..0fd78a476286 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 +456,39 @@ static int dump_btf_raw(const struct btf *btf,
return 0;
}
+static int dump_btf_kfuncs(struct btf_dump *d, const struct btf *btf)
+{
+ DECLARE_LIBBPF_OPTS(btf_dump_emit_type_decl_opts, opts);
+ int cnt = btf__type_cnt(btf);
+ int i;
+
+ for (i = 1; i < cnt; i++) {
+ const struct btf_type *t = btf__type_by_id(btf, i);
+ const struct btf_type *kft;
+ const char *name;
+ int err;
+
+ if (!btf_is_decl_tag(t))
+ continue;
+
+ name = btf__name_by_offset(btf, t->name_off);
+ if (strncmp(name, KFUNC_DECL_TAG, sizeof(KFUNC_DECL_TAG)))
+ continue;
+
+ printf("extern ");
+
+ kft = btf__type_by_id(btf, t->type);
+ opts.field_name = btf__name_by_offset(btf, kft->name_off);
+ err = btf_dump__emit_type_decl(d, kft->type, &opts);
+ if (err)
+ return err;
+
+ printf(" __weak __ksym;\n\n");
+ }
+
+ return 0;
+}
+
static void __printf(2, 0) btf_dump_printf(void *ctx,
const char *fmt, va_list args)
{
@@ -476,6 +511,12 @@ 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 +532,10 @@ 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");
--
2.42.1
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