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libbpf: Add support for dynamic tracepoints #8350

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29 changes: 28 additions & 1 deletion tools/lib/bpf/libbpf.c
Original file line number Diff line number Diff line change
Expand Up @@ -11623,11 +11623,34 @@ bpf_program__attach_kprobe_multi_opts(const struct bpf_program *prog,
return libbpf_err_ptr(err);
}

/* A dynamic tracepoint: "kprobe/SUBSYSTEM/PROBE" */
static int attach_dynamic_tracepoint(const struct bpf_program *prog, const char *func_name,
struct bpf_link **link)
{
char *tp_subsys, *tp_name;

tp_subsys = strdup(func_name);
if (!tp_subsys)
return -ENOMEM;

tp_name = strchr(tp_subsys, '/');
if (!tp_name) {
free(tp_subsys);
return -EINVAL;
}

*tp_name = '\0';
tp_name++;
*link = bpf_program__attach_tracepoint(prog, tp_subsys, tp_name);
free(tp_subsys);
return libbpf_get_error(*link);
}

static int attach_kprobe(const struct bpf_program *prog, long cookie, struct bpf_link **link)
{
DECLARE_LIBBPF_OPTS(bpf_kprobe_opts, opts);
const char *func_name, *dynamic_tp;
unsigned long offset = 0;
const char *func_name;
char *func;
int n;

Expand All @@ -11643,6 +11666,10 @@ static int attach_kprobe(const struct bpf_program *prog, long cookie, struct bpf
else
func_name = prog->sec_name + sizeof("kprobe/") - 1;

dynamic_tp = strchr(func_name, '/');
if (dynamic_tp)
return attach_dynamic_tracepoint(prog, func_name, link);

n = sscanf(func_name, "%m[a-zA-Z0-9_.]+%li", &func, &offset);
if (n < 1) {
pr_warn("kprobe name is invalid: %s\n", func_name);
Expand Down
64 changes: 64 additions & 0 deletions tools/testing/selftests/bpf/prog_tests/test_dynamic_tp.c
Original file line number Diff line number Diff line change
@@ -0,0 +1,64 @@
// SPDX-License-Identifier: GPL-2.0-only

#include <test_progs.h>
#include <bpf/btf.h>
#include <bpf/bpf.h>

#include "dynamic_tp.skel.h"

int dynamic_tp(const char *cmd)
{
const char *kprobe_file = "/sys/kernel/debug/tracing/kprobe_events";
ssize_t bytes_written;
int fd, err;

fd = open(kprobe_file, O_WRONLY | O_APPEND);
if (!ASSERT_GE(fd, 0, "open kprobe_events"))
return -1;

bytes_written = write(fd, cmd, strlen(cmd));
if (!ASSERT_GT(bytes_written, 0, "write kprobe_events")) {
close(fd);
return -1;
}

err = close(fd);
if (!ASSERT_OK(err, "close kprobe_events"))
return -1;
return 0;
}

void test_dynamic_tp(void)
{
struct dynamic_tp *skel;
pid_t child_pid;
int status, err;

/* create a dynamic tracepoint */
err = dynamic_tp("p:my_dynamic_tp kernel_clone");
if (!ASSERT_OK(err, "create dynamic tp"))
return;

skel = dynamic_tp__open_and_load();
if (!ASSERT_OK_PTR(skel, "load progs"))
goto remove_tp;
skel->bss->pid = getpid();
err = dynamic_tp__attach(skel);
if (!ASSERT_OK(err, "attach progs"))
goto cleanup;

/* trigger the dynamic tracepoint */
child_pid = fork();
if (!ASSERT_GT(child_pid, -1, "child_pid"))
goto cleanup;
if (child_pid == 0)
_exit(0);
waitpid(child_pid, &status, 0);

ASSERT_EQ(skel->bss->result, 1, "result");

cleanup:
dynamic_tp__destroy(skel);
remove_tp:
dynamic_tp("-:my_dynamic_tp kernel_clone");
}
27 changes: 27 additions & 0 deletions tools/testing/selftests/bpf/progs/dynamic_tp.c
Original file line number Diff line number Diff line change
@@ -0,0 +1,27 @@
// SPDX-License-Identifier: GPL-2.0

#include <vmlinux.h>
#include <bpf/bpf_helpers.h>

char _license[] SEC("license") = "GPL";

#define MAX_STACK_TRACE_DEPTH 32
unsigned long entries[MAX_STACK_TRACE_DEPTH] = {};
#define SIZE_OF_ULONG (sizeof(unsigned long))

int result, pid;

SEC("kprobe/kprobes/my_dynamic_tp")
int dynamic_tp(struct pt_regs *ctx)
{
int ret;

ret = bpf_get_stack(ctx, entries, MAX_STACK_TRACE_DEPTH * SIZE_OF_ULONG, 0);
if (ret < 0) {
result = -1;
return ret;
}
if (bpf_get_current_pid_tgid() >> 32 == pid)
result = 1;
return 0;
}
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