perf annotate: Work with vmlinux outside symfs

It is currently possible to use --symfs along with a vmlinux which lies
outside of the symfs by passing an absolute path to --vmlinux, thanks to
the check in dso__load_vmlinux() which handles this explicitly.

However, the annotate code lacks this check and thus 'perf annotate'
does not work ("Internal error: Invalid -1 error code") for kernel
functions with this combination.  Add the missing handling.

Signed-off-by: Vincent Whitchurch <vincent.whitchurch@axis.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: kernel@axis.com
Link: https://lore.kernel.org/r/20221125114210.2353820-1-vincent.whitchurch@axis.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/annotate.c

@@ -1731,7 +1731,10 @@ fallback:
 		 * cache, or is just a kallsyms file, well, lets hope that this
 		 * DSO is the same as when 'perf record' ran.
 		 */
-		__symbol__join_symfs(filename, filename_size, dso->long_name);
+		if (dso->kernel && dso->long_name[0] == '/')
+			snprintf(filename, filename_size, "%s", dso->long_name);
+		else
+			__symbol__join_symfs(filename, filename_size, dso->long_name);
 
 		mutex_lock(&dso->lock);
 		if (access(filename, R_OK) && errno == ENOENT && dso->nsinfo) {