From 5e3b8356de3623987ace530b1977ffeb9ecf5a8a Mon Sep 17 00:00:00 2001 From: Andrii Nakryiko Date: Sun, 15 Aug 2021 00:06:08 -0700 Subject: [PATCH] libbpf: Add uprobe ref counter offset support for USDT semaphores 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] a6ca88b241d5 ("trace_uprobe: support reference counter in fd-based uprobe") Signed-off-by: Andrii Nakryiko Signed-off-by: Daniel Borkmann Link: https://lore.kernel.org/bpf/20210815070609.987780-16-andrii@kernel.org --- tools/lib/bpf/libbpf.c | 17 +++++++++++++---- tools/lib/bpf/libbpf.h | 4 ++++ 2 files changed, 17 insertions(+), 4 deletions(-) diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c index 62ce878..88d8825 100644 --- a/tools/lib/bpf/libbpf.c +++ b/tools/lib/bpf/libbpf.c @@ -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", diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h index 1f4a672..f177d89 100644 --- a/tools/lib/bpf/libbpf.h +++ b/tools/lib/bpf/libbpf.h @@ -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 */ -- 2.7.4