a couple of usage fixups in prof

R=rsc
https://golang.org/cl/161050

diff --git a/src/cmd/prof/main.c b/src/cmd/prof/main.c
index 462aab9f6ccec9978afa74157513882e306934f2..2502b047c55f65be3794f9c61e013518005b5dc1 100644 (file)
--- a/src/cmd/prof/main.c
+++ b/src/cmd/prof/main.c
@@ -462,8 +462,14 @@ main(int argc, char *argv[])
        }
        if(argc > 0)
                file = argv[0];
-       else if(pid)
+       else if(pid) {
                file = proctextfile(pid);
+               if (file == NULL) {
+                       fprint(2, "prof: can't find file for pid %d: %r\n", pid);
+                       fprint(2, "prof: on Darwin, need to provide file name explicitly\n");
+                       exit(1);
+               }
+       }
        fd = open(file, 0);
        if(fd < 0) {
                fprint(2, "prof: can't open %s: %r\n", file);