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

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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: Alan Maguire <alan.maguire@oracle.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/1648654000-21758-2-git-send-email-alan.maguire@oracle.com
This commit is contained in:
Alan Maguire 2022-03-30 16:26:36 +01:00 committed by Andrii Nakryiko
parent 85bf1f5169
commit 1ce3a60e3c
1 changed files with 53 additions and 1 deletions
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54
tools/lib/bpf/libbpf.c
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@ -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);