On Fri, Mar 11, 2022 at 4:11 AM Alan Maguire <alan.maguire@xxxxxxxxxx> wrote:
>
> Now that u[ret]probes can use name-based specification, it makes
> sense to add support for auto-attach based on SEC() definition.
> The format proposed is
>
> SEC("u[ret]probe/prog:[raw_offset|[function_name[+offset]]")
nit: prog -> binary ? or prog -> path?
>
> For example, to trace malloc() in libc:
>
> SEC("uprobe/libc.so.6:malloc")
>
> ...or to trace function foo2 in /usr/bin/foo:
>
> SEC("uprobe//usr/bin/foo:foo2")
>
> Auto-attach is done for all tasks (pid -1). prog can be an absolute
> path or simply a program/library name; in the latter case, we use
> PATH/LD_LIBRARY_PATH to resolve the full path, falling back to
> standard locations (/usr/bin:/usr/sbin or /usr/lib64:/usr/lib) if
> the file is not found via environment-variable specified locations.
>
> Signed-off-by: Alan Maguire <alan.maguire@xxxxxxxxxx>
> ---
> tools/lib/bpf/libbpf.c | 68 ++++++++++++++++++++++++++++++++++++++++++++++++--
> 1 file changed, 66 insertions(+), 2 deletions(-)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 2b50b01..0dcbca8 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -8593,6 +8593,7 @@ int bpf_program__set_log_buf(struct bpf_program *prog, char *log_buf, size_t log
> }
>
> static int attach_kprobe(const struct bpf_program *prog, long cookie, struct bpf_link **link);
> +static int attach_uprobe(const struct bpf_program *prog, long cookie, struct bpf_link **link);
> static int attach_tp(const struct bpf_program *prog, long cookie, struct bpf_link **link);
> static int attach_raw_tp(const struct bpf_program *prog, long cookie, struct bpf_link **link);
> static int attach_trace(const struct bpf_program *prog, long cookie, struct bpf_link **link);
> @@ -8604,9 +8605,9 @@ int bpf_program__set_log_buf(struct bpf_program *prog, char *log_buf, size_t log
> SEC_DEF("sk_reuseport/migrate", SK_REUSEPORT, BPF_SK_REUSEPORT_SELECT_OR_MIGRATE, SEC_ATTACHABLE | SEC_SLOPPY_PFX),
> SEC_DEF("sk_reuseport", SK_REUSEPORT, BPF_SK_REUSEPORT_SELECT, SEC_ATTACHABLE | SEC_SLOPPY_PFX),
> SEC_DEF("kprobe/", KPROBE, 0, SEC_NONE, attach_kprobe),
> - SEC_DEF("uprobe/", KPROBE, 0, SEC_NONE),
> + SEC_DEF("uprobe/", KPROBE, 0, SEC_NONE, attach_uprobe),
> SEC_DEF("kretprobe/", KPROBE, 0, SEC_NONE, attach_kprobe),
> - SEC_DEF("uretprobe/", KPROBE, 0, SEC_NONE),
> + SEC_DEF("uretprobe/", KPROBE, 0, SEC_NONE, attach_uprobe),
> SEC_DEF("tc", SCHED_CLS, 0, SEC_NONE),
> SEC_DEF("classifier", SCHED_CLS, 0, SEC_NONE | SEC_SLOPPY_PFX | SEC_DEPRECATED),
> SEC_DEF("action", SCHED_ACT, 0, SEC_NONE | SEC_SLOPPY_PFX),
> @@ -10761,6 +10762,69 @@ struct bpf_link *bpf_program__attach_uprobe(const struct bpf_program *prog,
> return bpf_program__attach_uprobe_opts(prog, pid, binary_path, func_offset, &opts);
> }
>
> +/* Format of u[ret]probe section definition supporting auto-attach:
> + * u[ret]probe/prog:function[+offset]
same about prog
> + *
> + * prog can be an absolute/relative path or a filename; the latter is resolved to a
> + * full path via bpf_program__attach_uprobe_opts.
> + *
> + * Many uprobe programs do not avail of auto-attach, so we need to handle the
do not avail of? meaning "can't be auto-attached due to missing information"?
> + * case where the format is uprobe/myfunc by returning 0 with *link set to NULL
> + * to identify the case where auto-attach is not supported.
it's true that we supported SEC("uprobe/whatever") before and that's
not enough to auto-attach. But let's not drag this legacy "syntax"
forward. How about we check if LIBBPF_STRICT_SEC_NAME is set, and if
yes, then it should either be plain SEC("uprobe") or a proper full
form of SEC("uprobe/path:func...") that you are adding? libbpf
supports such case, you just need to change SEC_DEF definition to
uprobe/ -> uprobe+, which means that it is either SEC("uprobe") or
SEC("uprobe/<something>").
In legacy mode we just won't support auto-attach for uprobe.
Thoughts?
> + */
> +static int attach_uprobe(const struct bpf_program *prog, long cookie, struct bpf_link **link)
> +{
> + DECLARE_LIBBPF_OPTS(bpf_uprobe_opts, opts);
> + char *func, *probe_name, *func_end;
> + char *func_name, binary_path[512];
> + unsigned long long raw_offset;
> + size_t offset = 0;
> + int n;
> +
> + *link = NULL;
> +
[...]
