Commit 1ce3a60e authored by Alan Maguire's avatar Alan Maguire Committed by Andrii Nakryiko
Browse files

libbpf: auto-resolve programs/libraries when necessary for uprobes 



bpf_program__attach_uprobe_opts() requires a binary_path argument
specifying binary to instrument.  Supporting simply specifying
"libc.so.6" or "foo" should be possible too.

Library search checks LD_LIBRARY_PATH, then /usr/lib64, /usr/lib.
This allows users to run BPF programs prefixed with
LD_LIBRARY_PATH=/path2/lib while still searching standard locations.
Similarly for non .so files, we check PATH and /usr/bin, /usr/sbin.

Path determination will be useful for auto-attach of BPF uprobe programs
using SEC() definition.

Signed-off-by: default avatarAlan Maguire <alan.maguire@oracle.com>
Signed-off-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/1648654000-21758-2-git-send-email-alan.maguire@oracle.com
parent 85bf1f51

tools/lib/bpf/libbpf.c

+53 −1
Original line number Diff line number Diff line
@@ -10517,6 +10517,46 @@ static int perf_event_uprobe_open_legacy(const char *probe_name, bool retprobe, 
	return pfd;

}



/* Get full path to program/shared library. */

static int resolve_full_path(const char *file, char *result, size_t result_sz)

{

	const char *search_paths[2];

	int i;



	if (strstr(file, ".so")) {

		search_paths[0] = getenv("LD_LIBRARY_PATH");

		search_paths[1] = "/usr/lib64:/usr/lib";

	} else {

		search_paths[0] = getenv("PATH");

		search_paths[1] = "/usr/bin:/usr/sbin";

	}



	for (i = 0; i < ARRAY_SIZE(search_paths); i++) {

		const char *s;



		if (!search_paths[i])

			continue;

		for (s = search_paths[i]; s != NULL; s = strchr(s, ':')) {

			char *next_path;

			int seg_len;



			if (s[0] == ':')

				s++;

			next_path = strchr(s, ':');

			seg_len = next_path ? next_path - s : strlen(s);

			if (!seg_len)

				continue;

			snprintf(result, result_sz, "%.*s/%s", seg_len, s, file);

			/* ensure it is an executable file/link */

			if (access(result, R_OK | X_OK) < 0)

				continue;

			pr_debug("resolved '%s' to '%s'\n", file, result);

			return 0;

		}

	}

	return -ENOENT;

}



LIBBPF_API struct bpf_link *

bpf_program__attach_uprobe_opts(const struct bpf_program *prog, pid_t pid,

				const char *binary_path, size_t func_offset,
@@ -10524,6 +10564,7 @@ bpf_program__attach_uprobe_opts(const struct bpf_program *prog, pid_t pid, 
{

	DECLARE_LIBBPF_OPTS(bpf_perf_event_opts, pe_opts);

	char errmsg[STRERR_BUFSIZE], *legacy_probe = NULL;

	char full_binary_path[PATH_MAX];

	struct bpf_link *link;

	size_t ref_ctr_off;

	int pfd, err;
@@ -10536,12 +10577,23 @@ bpf_program__attach_uprobe_opts(const struct bpf_program *prog, pid_t pid, 
	ref_ctr_off = OPTS_GET(opts, ref_ctr_offset, 0);

	pe_opts.bpf_cookie = OPTS_GET(opts, bpf_cookie, 0);



	if (binary_path && !strchr(binary_path, '/')) {

		err = resolve_full_path(binary_path, full_binary_path,

					sizeof(full_binary_path));

		if (err) {

			pr_warn("prog '%s': failed to resolve full path for '%s'\n",

				prog->name, binary_path);

			return libbpf_err_ptr(err);

		}

		binary_path = full_binary_path;

	}



	legacy = determine_uprobe_perf_type() < 0;

	if (!legacy) {

		pfd = perf_event_open_probe(true /* uprobe */, retprobe, binary_path,

					    func_offset, pid, ref_ctr_off);

	} else {

		char probe_name[512];

		char probe_name[PATH_MAX + 64];



		if (ref_ctr_off)

			return libbpf_err_ptr(-EINVAL);