libbpf: Allow Golang symbols in uprobe secdef

Golang symbols in ELF files are different from C/C++
which contains special characters like '*', '(' and ')'.
With generics, things get more complicated, there are
symbols like:

  github.com/cilium/ebpf/internal.(*Deque[go.shape.interface { Format(fmt.State, int32); TypeName() string;github.com/cilium/ebpf/btf.copy() github.com/cilium/ebpf/btf.Type}]).Grow

Matching such symbols using `%m[^\n]` in sscanf, this
excludes newline which typically does not appear in ELF
symbols. This should work in most use-cases and also
work for unicode letters in identifiers. If newline do
show up in ELF symbols, users can still attach to such
symbol by specifying bpf_uprobe_opts::func_name.

A working example can be found at this repo ([0]).

  [0]: https://github.com/chenhengqi/libbpf-go-symbols

Suggested-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Hengqi Chen <hengqi.chen@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20230929155954.92448-1-hengqi.chen@gmail.com

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index b4758e54a81517eb0c2480ea075ae18d8be142eb..31b8b252e6143abe2242946a6196742ab670a2c1 100644 (file)
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -11114,7 +11114,7 @@ static int attach_uprobe_multi(const struct bpf_program *prog, long cookie, stru
 
        *link = NULL;
 
-       n = sscanf(prog->sec_name, "%m[^/]/%m[^:]:%ms",
+       n = sscanf(prog->sec_name, "%m[^/]/%m[^:]:%m[^\n]",
                   &probe_type, &binary_path, &func_name);
        switch (n) {
        case 1:
@@ -11624,14 +11624,14 @@ err_out:
 static int attach_uprobe(const struct bpf_program *prog, long cookie, struct bpf_link **link)
 {
        DECLARE_LIBBPF_OPTS(bpf_uprobe_opts, opts);
-       char *probe_type = NULL, *binary_path = NULL, *func_name = NULL;
-       int n, ret = -EINVAL;
+       char *probe_type = NULL, *binary_path = NULL, *func_name = NULL, *func_off;
+       int n, c, ret = -EINVAL;
        long offset = 0;
 
        *link = NULL;
 
-       n = sscanf(prog->sec_name, "%m[^/]/%m[^:]:%m[a-zA-Z0-9_.@]+%li",
-                  &probe_type, &binary_path, &func_name, &offset);
+       n = sscanf(prog->sec_name, "%m[^/]/%m[^:]:%m[^\n]",
+                  &probe_type, &binary_path, &func_name);
        switch (n) {
        case 1:
                /* handle SEC("u[ret]probe") - format is valid, but auto-attach is impossible. */
@@ -11642,7 +11642,17 @@ static int attach_uprobe(const struct bpf_program *prog, long cookie, struct bpf
                        prog->name, prog->sec_name);
                break;
        case 3:
-       case 4:
+               /* check if user specifies `+offset`, if yes, this should be
+                * the last part of the string, make sure sscanf read to EOL
+                */
+               func_off = strrchr(func_name, '+');
+               if (func_off) {
+                       n = sscanf(func_off, "+%li%n", &offset, &c);
+                       if (n == 1 && *(func_off + c) == '\0')
+                               func_off[0] = '\0';
+                       else
+                               offset = 0;
+               }
                opts.retprobe = strcmp(probe_type, "uretprobe") == 0 ||
                                strcmp(probe_type, "uretprobe.s") == 0;
                if (opts.retprobe && offset != 0) {