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libbpf: Add uprobe ref counter offset support for USDT semaphores

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When attaching to uprobes through perf subsystem, it's possible to specify
offset of a so-called USDT semaphore, which is just a reference counted u16,
used by kernel to keep track of how many tracers are attached to a given
location. Support for this feature was added in [0], so just wire this through
uprobe_opts. This is important to enable implementing USDT attachment and
tracing through libbpf's bpf_program__attach_uprobe_opts() API.

  [0] a6ca88b241 ("trace_uprobe: support reference counter in fd-based uprobe")

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20210815070609.987780-16-andrii@kernel.org
This commit is contained in:
Andrii Nakryiko 2021-08-15 00:06:08 -07:00 committed by Daniel Borkmann
parent 0a80cf67f3
commit 5e3b8356de
2 changed files with 17 additions and 4 deletions
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17
tools/lib/bpf/libbpf.c
View File

@ -9152,13 +9152,19 @@ static int determine_uprobe_retprobe_bit(void)
return parse_uint_from_file(file, "config:%d\n");
}
#define PERF_UPROBE_REF_CTR_OFFSET_BITS 32
#define PERF_UPROBE_REF_CTR_OFFSET_SHIFT 32
static int perf_event_open_probe(bool uprobe, bool retprobe, const char *name,
uint64_t offset, int pid)
uint64_t offset, int pid, size_t ref_ctr_off)
{
struct perf_event_attr attr = {};
char errmsg[STRERR_BUFSIZE];
int type, pfd, err;
if (ref_ctr_off >= (1ULL << PERF_UPROBE_REF_CTR_OFFSET_BITS))
return -EINVAL;
type = uprobe ? determine_uprobe_perf_type()
: determine_kprobe_perf_type();
if (type < 0) {
@ -9181,6 +9187,7 @@ static int perf_event_open_probe(bool uprobe, bool retprobe, const char *name,
}
attr.size = sizeof(attr);
attr.type = type;
attr.config |= (__u64)ref_ctr_off << PERF_UPROBE_REF_CTR_OFFSET_SHIFT;
attr.config1 = ptr_to_u64(name); /* kprobe_func or uprobe_path */
attr.config2 = offset; /* kprobe_addr or probe_offset */
@ -9219,7 +9226,7 @@ bpf_program__attach_kprobe_opts(struct bpf_program *prog,
pe_opts.bpf_cookie = OPTS_GET(opts, bpf_cookie, 0);
pfd = perf_event_open_probe(false /* uprobe */, retprobe, func_name,
offset, -1 /* pid */);
offset, -1 /* pid */, 0 /* ref_ctr_off */);
if (pfd < 0) {
pr_warn("prog '%s': failed to create %s '%s' perf event: %s\n",
prog->name, retprobe ? "kretprobe" : "kprobe", func_name,
@ -9289,6 +9296,7 @@ bpf_program__attach_uprobe_opts(struct bpf_program *prog, pid_t pid,
DECLARE_LIBBPF_OPTS(bpf_perf_event_opts, pe_opts);
char errmsg[STRERR_BUFSIZE];
struct bpf_link *link;
size_t ref_ctr_off;
int pfd, err;
bool retprobe;
@ -9296,10 +9304,11 @@ bpf_program__attach_uprobe_opts(struct bpf_program *prog, pid_t pid,
return libbpf_err_ptr(-EINVAL);
retprobe = OPTS_GET(opts, retprobe, false);
ref_ctr_off = OPTS_GET(opts, ref_ctr_offset, 0);
pe_opts.bpf_cookie = OPTS_GET(opts, bpf_cookie, 0);
pfd = perf_event_open_probe(true /* uprobe */, retprobe,
binary_path, func_offset, pid);
pfd = perf_event_open_probe(true /* uprobe */, retprobe, binary_path,
func_offset, pid, ref_ctr_off);
if (pfd < 0) {
pr_warn("prog '%s': failed to create %s '%s:0x%zx' perf event: %s\n",
prog->name, retprobe ? "uretprobe" : "uprobe",

4
tools/lib/bpf/libbpf.h
View File

@ -284,6 +284,10 @@ bpf_program__attach_kprobe_opts(struct bpf_program *prog,
struct bpf_uprobe_opts {
/* size of this struct, for forward/backward compatiblity */
size_t sz;
/* offset of kernel reference counted USDT semaphore, added in
* a6ca88b241d5 ("trace_uprobe: support reference counter in fd-based uprobe")
*/
size_t ref_ctr_offset;
/* custom user-provided value fetchable through bpf_get_attach_cookie() */
__u64 bpf_cookie;
/* uprobe is return probe, invoked at function return time */