perf buildid-cache: Fix symbolic link handling

This was broken since link(2) doesn't dereference symbolic
links. Instead 'filename' becomes a symbolic link to the same file
that 'name' refers to.

This had the bad effect to create dangling symlinks in the case that
even can't be removed with perf-buildid-cache(1).

LKML-Reference: <[e-mail]>
Signed-off-by: Franck Bui-Huu <[e-mail]>
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/util/header.c

···
 			  const char *name, bool is_kallsyms)
 {
 	const size_t size = PATH_MAX;
-	char *filename = malloc(size),
+	char *realname = realpath(name, NULL),
+	     *filename = malloc(size),
 	     *linkname = malloc(size), *targetname;
 	int len, err = -1;
 
-	if (filename == NULL || linkname == NULL)
+	if (realname == NULL || filename == NULL || linkname == NULL)
 		goto out_free;
 
 	len = snprintf(filename, size, "%s%s%s",
-		       debugdir, is_kallsyms ? "/" : "", name);
+		       debugdir, is_kallsyms ? "/" : "", realname);
 	if (mkdir_p(filename, 0755))
 		goto out_free;
 
···
 		if (is_kallsyms) {
 			 if (copyfile("/proc/kallsyms", filename))
 				goto out_free;
-		} else if (link(name, filename) && copyfile(name, filename))
+		} else if (link(realname, filename) && copyfile(name, filename))
 			goto out_free;
 	}
 
···
 	if (symlink(targetname, linkname) == 0)
 		err = 0;
 out_free:
+	free(realname);
 	free(filename);
 	free(linkname);
 	return err;