Add support for name-based attach to Userland Static-Defined Tracing
(USDT) probes via lookup of ELF notes associated with probe definition.
ELF notes are consulted for probe offset, and - if "is-enabled" style
of probing is in use - semaphore offset.
Signed-off-by: Alan Maguire <alan.maguire@xxxxxxxxxx>
---
tools/lib/bpf/libbpf.c | 84 ++++++++++++++++++++++++++++++++++++++++++++++----
tools/lib/bpf/libbpf.h | 9 +++++-
2 files changed, 86 insertions(+), 7 deletions(-)
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index bccc26a..cdcd799 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -10275,6 +10275,52 @@ static ssize_t find_elf_func_offset(Elf *elf, const char *name)
return ret;
}
+struct sdt_note {
+ uint64_t pc;
+ uint64_t base_addr;
+ uint64_t semaphore;
+ const char provider_probe[256];
+};
+
+/* Find offset of USDT probe in object specified in ELF notes.
+ * Note may also specify semaphore offset, record value in *semaphore_offp.
+ */
+static ssize_t find_elf_usdt_offset(Elf *elf, const char *provider,
+ const char *name, ssize_t *semaphore_offp)
+{
+ Elf_Data *data = NULL;
+ Elf_Scn *scn = NULL;
+
+ while ((scn = find_elfscn(elf, SHT_NOTE, scn)) > 0) {
+ while ((data = elf_getdata(scn, data)) != 0) {
+ size_t name_off, desc_off, off;
+ GElf_Nhdr nhdr;
+
+ while ((off = gelf_getnote(data, off, &nhdr,
+ &name_off, &desc_off)) != 0) {
+ struct sdt_note *sdt_note;
+ const char *probe;
+
+ if (nhdr.n_namesz != 8 ||
+ memcmp((char *)data->d_buf + name_off, "stapsdt", 8) != 0)
+ continue;
+ sdt_note = (struct sdt_note *)(data->d_buf + desc_off);
+ if (strcmp(provider, sdt_note->provider_probe) != 0)
+ continue;
+ /* probe is after null-terminated provider */
+ probe = sdt_note->provider_probe +
+ strlen(sdt_note->provider_probe) + 1;
+ if (strcmp(probe, name) != 0)
+ continue;
+
+ *semaphore_offp = (ssize_t)sdt_note->semaphore;
+ return (ssize_t)sdt_note->pc;
+ }
+ }
+ }
+ 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,
@@ -10286,7 +10332,7 @@ static ssize_t find_elf_func_offset(Elf *elf, const char *name)
size_t ref_ctr_off;
int pfd, err;
bool retprobe, legacy;
- const char *func_name;
+ const char *func_name, *usdt_name, *usdt_provider;
if (!OPTS_VALID(opts, bpf_uprobe_opts))
return libbpf_err_ptr(-EINVAL);
@@ -10296,11 +10342,25 @@ static ssize_t find_elf_func_offset(Elf *elf, const char *name)
pe_opts.bpf_cookie = OPTS_GET(opts, bpf_cookie, 0);
func_name = OPTS_GET(opts, func_name, NULL);
- if (func_name) {
- ssize_t sym_off, rel_off;
+ usdt_provider = OPTS_GET(opts, usdt_provider, NULL);
+ usdt_name = OPTS_GET(opts, usdt_name, NULL);
+ if (func_name || usdt_name) {
+ ssize_t sym_off, rel_off, semaphore_off = 0;
Elf *elf;
int fd;
+ if (func_name && usdt_name) {
+ pr_warn("both func_name and usdt_name cannot be specified\n");
+ return libbpf_err_ptr(-EINVAL);
+ }
+ if (usdt_name && (func_offset || ref_ctr_off)) {
+ pr_warn("func_offset argument, ref_ctr_off option should be 0 when usdt_name is used\n");
+ return libbpf_err_ptr(-EINVAL);
+ }
+ if (usdt_name && !usdt_provider) {
+ pr_warn("usdt_provider and usdt_name must be supplied\n");
+ return libbpf_err_ptr(-EINVAL);
+ }
if (pid == -1) {
/* system-wide probing is not supported; we need
* a running process to determine offsets.
@@ -10330,20 +10390,32 @@ static ssize_t find_elf_func_offset(Elf *elf, const char *name)
close(fd);
return libbpf_err_ptr(-LIBBPF_ERRNO__FORMAT);
}
- sym_off = find_elf_func_offset(elf, func_name);
+ if (func_name)
+ sym_off = find_elf_func_offset(elf, func_name);
+ else
+ sym_off = find_elf_usdt_offset(elf, usdt_provider, usdt_name,
+ &semaphore_off);
close(fd);
elf_end(elf);
if (sym_off < 0) {
- pr_debug("could not find sym offset for %s\n", func_name);
+ pr_debug("could not find sym offset for %s\n", func_name ?: usdt_name);
return libbpf_err_ptr(sym_off);
}
rel_off = get_rel_offset(pid, sym_off);
if (rel_off < 0) {
pr_debug("could not find relative offset for %s at 0x%lx\n",
- func_name, sym_off);
+ func_name ?: usdt_name, sym_off);
return libbpf_err_ptr(rel_off);
}
func_offset += (size_t)rel_off;
+ if (semaphore_off) {
+ ref_ctr_off = get_rel_offset(pid, semaphore_off);
+ if (ref_ctr_off < 0) {
+ pr_debug("could not find relative offset for semaphore for %s at 0x%lx\n",
+ usdt_name, semaphore_off);
+ return libbpf_err_ptr(ref_ctr_off);
+ }
+ }
}
legacy = determine_uprobe_perf_type() < 0;
diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index 40cb5ae..fcad6b1 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -439,9 +439,16 @@ struct bpf_uprobe_opts {
* argument to specify argument _within_ the function.
*/
const char *func_name;
+ /* name of USDT (Userland Static-Defined Tracing) provider/probe.
+ * Offsets of USDT probe and associated semaphore (if any) are found
+ * in ELF notes. Note that if usdt_name is specified, func_offset
+ * argument and ref_ctr_offset values should be zero.
+ */
+ const char *usdt_provider;
+ const char *usdt_name;
size_t :0;
};
-#define bpf_uprobe_opts__last_field func_name
+#define bpf_uprobe_opts__last_field usdt_name
/**
* @brief **bpf_program__attach_uprobe()** attaches a BPF program
--
1.8.3.1
