| Message ID | 1648654000-21758-2-git-send-email-alan.maguire@oracle.com (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | 1ce3a60e3c287479f15147ffc61c35b2e436a0d5 |
| Delegated to: | BPF |
| Headers | show |
| Series | libbpf: name-based u[ret]probe attach | expand |
On Wed, Mar 30, 2022 at 8:27 AM Alan Maguire <alan.maguire@oracle.com> wrote: > > 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> > --- This patch's subject was very long, I took the liberty to shorten it as: libbpf: auto-resolve programs/libraries when necessary for uprobes Please yell if you strongly object. > tools/lib/bpf/libbpf.c | 53 +++++++++++++++++++++++++++++++++++++++++++++++++- > 1 file changed, 52 insertions(+), 1 deletion(-) > > diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c > index 809fe20..a7d5954 100644 > --- a/tools/lib/bpf/libbpf.c > +++ b/tools/lib/bpf/libbpf.c > @@ -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")) { this check can be too brittle. It will think that binary called "i.am.sorry" will be re assumed a shared library. While you can always subvert this logic, maybe checking for ".so" suffix (not a substring) and, if no such suffix found, looking for ".so." substring as a second check? "i.am.so.sorry" still would fool it, but that looks like a very artificial stretch. let's improve this in a follow up > + search_paths[0] = getenv("LD_LIBRARY_PATH"); > + search_paths[1] = "/usr/lib64:/usr/lib"; [...] > { > 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 +10577,22 @@ static int perf_event_uprobe_open_legacy(const char *probe_name, bool retprobe, > 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("failed to resolve full path for '%s'\n", binary_path); we use "prog '%s': " prefix for error messages within bpf_program__attach_xxx() wherever possible. Fixed up while applying. > + 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); > -- > 1.8.3.1 >
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c index 809fe20..a7d5954 100644 --- a/tools/lib/bpf/libbpf.c +++ b/tools/lib/bpf/libbpf.c @@ -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 @@ static int perf_event_uprobe_open_legacy(const char *probe_name, bool retprobe, { 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 +10577,22 @@ static int perf_event_uprobe_open_legacy(const char *probe_name, bool retprobe, 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("failed to resolve full path for '%s'\n", 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);
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> --- tools/lib/bpf/libbpf.c | 53 +++++++++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 52 insertions(+), 1 deletion(-)