Messages in this thread |  | | From | Hoyeon Lee <> | | Date | Wed, 1 Apr 2026 14:21:28 +0900 | | Subject | Re: [PATCH bpf-next v4 1/2] libbpf: clarify raw-address single kprobe attach behavior |
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On Wed, Apr 1, 2026 at 8:05 AM Andrii Nakryiko <andrii.nakryiko@gmail.com> wrote: > > On Tue, Mar 31, 2026 at 8:25 AM Hoyeon Lee <hoyeon.lee@suse.com> wrote: > > > > bpf_program__attach_kprobe_opts() documents single-kprobe attach > > through func_name, with an optional offset. For the PMU-based > > non-legacy path, func_name = NULL with an absolute address in offset > > already works as well, but that is not described in the API. > > > > This commit clarifies this existing non-legacy behavior. For PMU-based > > attach, callers can use func_name = NULL with an absolute address in > > offset as the raw-address form. For legacy tracefs/debugfs kprobes, > > reject this form explicitly. > > > > Signed-off-by: Hoyeon Lee <hoyeon.lee@suse.com> > > --- > > tools/lib/bpf/libbpf.c | 21 ++++++++++++--------- > > tools/lib/bpf/libbpf.h | 3 ++- > > 2 files changed, 14 insertions(+), 10 deletions(-) > > > > diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c > > index 9ea41f40dc82..9083f542a3b0 100644 > > --- a/tools/lib/bpf/libbpf.c > > +++ b/tools/lib/bpf/libbpf.c > > @@ -11523,7 +11523,8 @@ static int determine_uprobe_retprobe_bit(void) > > #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, size_t ref_ctr_off) > > + uint64_t offset_or_addr, int pid, > > don't rename it, keep it as "offset" >
Got it, I'll drop it in v5.
> > + size_t ref_ctr_off) > > { > > const size_t attr_sz = sizeof(struct perf_event_attr); > > struct perf_event_attr attr; > > @@ -11558,7 +11559,7 @@ static int perf_event_open_probe(bool uprobe, bool retprobe, const char *name, > > 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 */ > > + attr.config2 = offset_or_addr; /* kprobe_addr or probe_offset */ > > > > /* pid filter is meaningful only for uprobes */ > > pfd = syscall(__NR_perf_event_open, &attr, > > @@ -11816,6 +11817,8 @@ bpf_program__attach_kprobe_opts(const struct bpf_program *prog, > > default: > > return libbpf_err_ptr(-EINVAL); > > } > > + if (!func_name && legacy) > > + return libbpf_err_ptr(-ENOTSUP); > > -EOPNOTSUPP > > pw-bot: cr > > > > > if (!legacy) { > > pfd = perf_event_open_probe(false /* uprobe */, retprobe, > > @@ -11835,21 +11838,21 @@ bpf_program__attach_kprobe_opts(const struct bpf_program *prog, > > offset, -1 /* pid */); > > } > > if (pfd < 0) { > > - err = -errno; > > - pr_warn("prog '%s': failed to create %s '%s+0x%zx' perf event: %s\n", > > + err = pfd; > > + pr_warn("prog '%s': failed to create %s '%s%s0x%zx' perf event: %s\n", > > prog->name, retprobe ? "kretprobe" : "kprobe", > > - func_name, offset, > > - errstr(err)); > > + func_name ?: "", func_name ? "+" : "", > > + offset, errstr(err)); > > goto err_out; > > } > > link = bpf_program__attach_perf_event_opts(prog, pfd, &pe_opts); > > err = libbpf_get_error(link); > > if (err) { > > close(pfd); > > - pr_warn("prog '%s': failed to attach to %s '%s+0x%zx': %s\n", > > + pr_warn("prog '%s': failed to attach to %s '%s%s0x%zx': %s\n", > > prog->name, retprobe ? "kretprobe" : "kprobe", > > - func_name, offset, > > - errstr(err)); > > + func_name ?: "", func_name ? "+" : "", > > + offset, errstr(err)); > > goto err_clean_legacy; > > } > > if (legacy) { > > diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h > > index 0be34852350f..f75f3ab0f20c 100644 > > --- a/tools/lib/bpf/libbpf.h > > +++ b/tools/lib/bpf/libbpf.h > > @@ -557,7 +557,7 @@ struct bpf_kprobe_opts { > > size_t sz; > > /* custom user-provided value fetchable through bpf_get_attach_cookie() */ > > __u64 bpf_cookie; > > - /* function's offset to install kprobe to */ > > + /* function offset, or raw address if func_name == NULL (non-legacy) */ > > legacy mode will be useful on very-very old kernels only, let's not > distract with constant mentions for "non-legacy", please remove > "(non-legacy)" here and other legacy mentions above > > > but also, while you are at it, let's add a proper doc comment to > bpf_program__attach_kprobe and bpf_program__attach_kprobe_opts APIs? > That seems like a more obvious place to explain name+offset and offset > as absolute address behavior, IMO >
Right. I'll drop the "(non-legacy)" wording and add proper API documentation to bpf_program__attach_kprobe() and bpf_program__attach_kprobe_opts() in v5.
> > size_t offset; > > /* kprobe is return probe */ > > bool retprobe; > > @@ -565,6 +565,7 @@ struct bpf_kprobe_opts { > > enum probe_attach_mode attach_mode; > > size_t :0; > > }; > > + > > #define bpf_kprobe_opts__last_field attach_mode > > > > LIBBPF_API struct bpf_link * > > -- > > 2.52.0 > >
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