examples/c: improve uprobe with function name

The code changes in this commit improve the functionality
of the uprobe by using the function name instead of the
function offset. This change is made to simplify the code
and make it more readable.

Signed-off-by: yunwei37 <[email protected]>

examples/c/uprobe.c

@@ -12,37 +12,6 @@ static int libbpf_print_fn(enum libbpf_print_level level, const char *format, va
 	return vfprintf(stderr, format, args);
 }
 
-/*
- * Taken from https://github.com/torvalds/linux/blob/9b59ec8d50a1f28747ceff9a4f39af5deba9540e/tools/testing/selftests/bpf/trace_helpers.c#L149-L205
- *
- * See discussion in https://github.com/libbpf/libbpf-bootstrap/pull/90
- */
-ssize_t get_uprobe_offset(const void *addr)
-{
-	size_t start, end, base;
-	char buf[256];
-	bool found = false;
-	FILE *f;
-
-	f = fopen("/proc/self/maps", "r");
-	if (!f)
-		return -errno;
-
-	while (fscanf(f, "%zx-%zx %s %zx %*[^\n]\n", &start, &end, buf, &base) == 4) {
-		if (buf[2] == 'x' && (uintptr_t)addr >= start && (uintptr_t)addr < end) {
-			found = true;
-			break;
-		}
-	}
-
-	fclose(f);
-
-	if (!found)
-		return -ESRCH;
-
-	return (uintptr_t)addr - start + base;
-}
-
 /* It's a global function to make sure compiler doesn't inline it. */
 int uprobed_add(int a, int b)
 {
@@ -57,8 +26,8 @@ int uprobed_sub(int a, int b)
 int main(int argc, char **argv)
 {
 	struct uprobe_bpf *skel;
-	long uprobe_offset;
 	int err, i;
+	LIBBPF_OPTS(bpf_uprobe_opts, uprobe_opts);
 
 	/* Set up libbpf errors and debug info callback */
 	libbpf_set_print(libbpf_print_fn);
@@ -70,20 +39,18 @@ int main(int argc, char **argv)
 		return 1;
 	}
 
+	/* Attach tracepoint handler */
+	uprobe_opts.func_name = "uprobed_add";
+	uprobe_opts.retprobe = false;
 	/* uprobe/uretprobe expects relative offset of the function to attach
-	 * to. This offset is relateve to the process's base load address. So
-	 * easy way to do this is to take an absolute address of the desired
-	 * function and substract base load address from it.  If we were to
-	 * parse ELF to calculate this function, we'd need to add .text
-	 * section offset and function's offset within .text ELF section.
+	 * to. libbpf will automatically find the offset for us if we provide the
+	 * function name. If the function name is not specified, libbpf will try
+	 * to use the function offset instead.
 	 */
-	uprobe_offset = get_uprobe_offset(&uprobed_add);
-
-	/* Attach tracepoint handler */
-	skel->links.uprobe_add =
-		bpf_program__attach_uprobe(skel->progs.uprobe_add, false /* not uretprobe */,
-					   0 /* self pid */, "/proc/self/exe", uprobe_offset);
-
+	skel->links.uprobe_add = bpf_program__attach_uprobe_opts(skel->progs.uprobe_add,
+								 0 /* self pid */, "/proc/self/exe",
+								 0 /* offset for function */,
+								 &uprobe_opts /* opts */);
 	if (!skel->links.uprobe_add) {
 		err = -errno;
 		fprintf(stderr, "Failed to attach uprobe: %d\n", err);
@@ -94,10 +61,11 @@ int main(int argc, char **argv)
 	 * processes that use the same binary executable; to do that we need
 	 * to specify -1 as PID, as we do here
 	 */
-	skel->links.uretprobe_add =
-		bpf_program__attach_uprobe(skel->progs.uretprobe_add, true /* uretprobe */,
-					   -1 /* any pid */, "/proc/self/exe", uprobe_offset);
-
+	uprobe_opts.func_name = "uprobed_add";
+	uprobe_opts.retprobe = true;
+	skel->links.uretprobe_add = bpf_program__attach_uprobe_opts(
+		skel->progs.uretprobe_add, -1 /* self pid */, "/proc/self/exe",
+		0 /* offset for function */, &uprobe_opts /* opts */);
 	if (!skel->links.uretprobe_add) {
 		err = -errno;
 		fprintf(stderr, "Failed to attach uprobe: %d\n", err);