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Message-Id: <20250430164608.3790552-2-chen.dylane@linux.dev>
Date: Thu, 1 May 2025 00:46:07 +0800
From: Tao Chen <chen.dylane@...ux.dev>
To: ast@...nel.org,
daniel@...earbox.net,
john.fastabend@...il.com,
andrii@...nel.org,
martin.lau@...ux.dev,
eddyz87@...il.com,
song@...nel.org,
yonghong.song@...ux.dev,
kpsingh@...nel.org,
sdf@...ichev.me,
haoluo@...gle.com,
jolsa@...nel.org,
alan.maguire@...cle.com
Cc: bpf@...r.kernel.org,
linux-kernel@...r.kernel.org,
Tao Chen <chen.dylane@...ux.dev>
Subject: [RFC PATCH bpf-next 1/2] libbpf: Try get fentry func addr from available_filter_functions_addr
Try to get the real kernel func addr from available_filter_functions_addr,
in case of the function name is optimized by the compiler and a suffix
such as ".isra.0" is added, which will be used in the next patch.
Signed-off-by: Tao Chen <chen.dylane@...ux.dev>
---
tools/include/uapi/linux/bpf.h | 1 +
tools/lib/bpf/bpf.c | 1 +
tools/lib/bpf/bpf.h | 1 +
tools/lib/bpf/gen_loader.c | 1 +
tools/lib/bpf/libbpf.c | 53 ++++++++++++++++++++++++++++++++++
5 files changed, 57 insertions(+)
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 07ee73cdf9..7016e47a70 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -1577,6 +1577,7 @@ union bpf_attr {
* If provided, prog_flags should have BPF_F_TOKEN_FD flag set.
*/
__s32 prog_token_fd;
+ __aligned_u64 fentry_func;
/* The fd_array_cnt can be used to pass the length of the
* fd_array array. In this case all the [map] file descriptors
* passed in this array will be bound to the program, even if
diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
index a9c3e33d0f..639a6b54e8 100644
--- a/tools/lib/bpf/bpf.c
+++ b/tools/lib/bpf/bpf.c
@@ -312,6 +312,7 @@ int bpf_prog_load(enum bpf_prog_type prog_type,
attr.fd_array = ptr_to_u64(OPTS_GET(opts, fd_array, NULL));
attr.fd_array_cnt = OPTS_GET(opts, fd_array_cnt, 0);
+ attr.fentry_func = OPTS_GET(opts, fentry_func, 0);
if (log_level) {
attr.log_buf = ptr_to_u64(log_buf);
diff --git a/tools/lib/bpf/bpf.h b/tools/lib/bpf/bpf.h
index 777627d33d..b3340bcf7b 100644
--- a/tools/lib/bpf/bpf.h
+++ b/tools/lib/bpf/bpf.h
@@ -83,6 +83,7 @@ struct bpf_prog_load_opts {
__u32 attach_btf_id;
__u32 attach_prog_fd;
__u32 attach_btf_obj_fd;
+ __u64 fentry_func;
const int *fd_array;
diff --git a/tools/lib/bpf/gen_loader.c b/tools/lib/bpf/gen_loader.c
index 113ae4abd3..d90874b746 100644
--- a/tools/lib/bpf/gen_loader.c
+++ b/tools/lib/bpf/gen_loader.c
@@ -1023,6 +1023,7 @@ void bpf_gen__prog_load(struct bpf_gen *gen,
attr.kern_version = 0;
attr.insn_cnt = tgt_endian((__u32)insn_cnt);
attr.prog_flags = tgt_endian(load_attr->prog_flags);
+ attr.fentry_func = tgt_endian(load_attr->fentry_func);
attr.func_info_rec_size = tgt_endian(load_attr->func_info_rec_size);
attr.func_info_cnt = tgt_endian(load_attr->func_info_cnt);
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 37d563e140..624e75cf2f 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -7456,6 +7456,50 @@ static int libbpf_prepare_prog_load(struct bpf_program *prog,
}
static void fixup_verifier_log(struct bpf_program *prog, char *buf, size_t buf_sz);
+static const char *tracefs_available_filter_functions_addrs(void);
+
+static void try_get_fentry_func_addr(const char *func_name, struct bpf_prog_load_opts *load_attr)
+{
+ const char *available_functions_file = tracefs_available_filter_functions_addrs();
+ char sym_name[500];
+ FILE *f;
+ char *suffix;
+ int ret;
+ unsigned long long sym_addr;
+
+ f = fopen(available_functions_file, "re");
+ if (!f) {
+ pr_warn("failed to open %s: %s\n", available_functions_file, errstr(errno));
+ return;
+ }
+
+ while (true) {
+ ret = fscanf(f, "%llx %499s%*[^\n]\n", &sym_addr, sym_name);
+ if (ret == EOF && feof(f))
+ break;
+
+ if (ret != 2) {
+ pr_warn("failed to parse available_filter_functions_addrs entry: %d\n",
+ ret);
+ goto cleanup;
+ }
+
+ if (strcmp(func_name, sym_name) == 0) {
+ load_attr->fentry_func = sym_addr;
+ break;
+ }
+ /* find [func_name] optimized by compiler like [func_name].isra.0 */
+ suffix = strstr(sym_name, ".");
+ if (suffix && strncmp(sym_name, func_name,
+ strlen(sym_name) - strlen(suffix)) == 0) {
+ load_attr->fentry_func = sym_addr;
+ break;
+ }
+ }
+
+cleanup:
+ fclose(f);
+}
static int bpf_object_load_prog(struct bpf_object *obj, struct bpf_program *prog,
struct bpf_insn *insns, int insns_cnt,
@@ -7504,6 +7548,15 @@ static int bpf_object_load_prog(struct bpf_object *obj, struct bpf_program *prog
load_attr.prog_ifindex = prog->prog_ifindex;
load_attr.expected_attach_type = prog->expected_attach_type;
+ if (load_attr.expected_attach_type == BPF_TRACE_FENTRY ||
+ load_attr.expected_attach_type == BPF_TRACE_FEXIT) {
+ const char *func_name;
+
+ func_name = strchr(prog->sec_name, '/');
+ if (func_name)
+ try_get_fentry_func_addr(++func_name, &load_attr);
+ }
+
/* specify func_info/line_info only if kernel supports them */
if (obj->btf && btf__fd(obj->btf) >= 0 && kernel_supports(obj, FEAT_BTF_FUNC)) {
load_attr.prog_btf_fd = btf__fd(obj->btf);
--
2.43.0
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