libbpf: Improve string parsing for uprobe auto-attach

For uprobe auto-attach, the parsing can be simplified for the SEC()
name to a single sscanf(); the return value of the sscanf can then
be used to distinguish between sections that simply specify
"u[ret]probe" (and thus cannot auto-attach), those that specify
"u[ret]probe/binary_path:function+offset" etc.

Suggested-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/1649245431-29956-3-git-send-email-alan.maguire@oracle.com

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index c92226a..016ecdd 100644 (file)
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -10913,60 +10913,45 @@ 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 *func, *probe_name, *func_end;
-       char *func_name, binary_path[512];
-       unsigned long long raw_offset;
-       size_t offset = 0;
-       int n;
+       char *probe_type = NULL, *binary_path = NULL, *func_name = NULL;
+       int n, ret = -EINVAL;
+       long offset = 0;
 
        *link = NULL;
 
-       opts.retprobe = str_has_pfx(prog->sec_name, "uretprobe");
-       if (opts.retprobe)
-               probe_name = prog->sec_name + sizeof("uretprobe") - 1;
-       else
-               probe_name = prog->sec_name + sizeof("uprobe") - 1;
-       if (probe_name[0] == '/')
-               probe_name++;
-
-       /* handle SEC("u[ret]probe") - format is valid, but auto-attach is impossible. */
-       if (strlen(probe_name) == 0)
-               return 0;
-
-       snprintf(binary_path, sizeof(binary_path), "%s", probe_name);
-       /* ':' should be prior to function+offset */
-       func_name = strrchr(binary_path, ':');
-       if (!func_name) {
-               pr_warn("section '%s' missing ':function[+offset]' specification\n",
+       n = sscanf(prog->sec_name, "%m[^/]/%m[^:]:%m[a-zA-Z0-9_.]+%li",
+                  &probe_type, &binary_path, &func_name, &offset);
+       switch (n) {
+       case 1:
+               /* handle SEC("u[ret]probe") - format is valid, but auto-attach is impossible. */
+               ret = 0;
+               break;
+       case 2:
+               pr_warn("prog '%s': section '%s' missing ':function[+offset]' specification\n",
+                       prog->name, prog->sec_name);
+               break;
+       case 3:
+       case 4:
+               opts.retprobe = strcmp(probe_type, "uretprobe") == 0;
+               if (opts.retprobe && offset != 0) {
+                       pr_warn("prog '%s': uretprobes do not support offset specification\n",
+                               prog->name);
+                       break;
+               }
+               opts.func_name = func_name;
+               *link = bpf_program__attach_uprobe_opts(prog, -1, binary_path, offset, &opts);
+               ret = libbpf_get_error(*link);
+               break;
+       default:
+               pr_warn("prog '%s': invalid format of section definition '%s'\n", prog->name,
                        prog->sec_name);
-               return -EINVAL;
-       }
-       func_name[0] = '\0';
-       func_name++;
-       n = sscanf(func_name, "%m[a-zA-Z0-9_.]+%li", &func, &offset);
-       if (n < 1) {
-               pr_warn("uprobe name '%s' is invalid\n", func_name);
-               return -EINVAL;
-       }
-       if (opts.retprobe && offset != 0) {
-               free(func);
-               pr_warn("uretprobes do not support offset specification\n");
-               return -EINVAL;
-       }
-
-       /* Is func a raw address? */
-       errno = 0;
-       raw_offset = strtoull(func, &func_end, 0);
-       if (!errno && !*func_end) {
-               free(func);
-               func = NULL;
-               offset = (size_t)raw_offset;
+               break;
        }
-       opts.func_name = func;
+       free(probe_type);
+       free(binary_path);
+       free(func_name);
 
-       *link = bpf_program__attach_uprobe_opts(prog, -1, binary_path, offset, &opts);
-       free(func);
-       return libbpf_get_error(*link);
+       return ret;
 }
 
 struct bpf_link *bpf_program__attach_uprobe(const struct bpf_program *prog,