gc: fix build (signed char bug)

R=ken2
CC=golang-dev
https://golang.org/cl/210043

diff --git a/src/cmd/gc/subr.c b/src/cmd/gc/subr.c
index 7072d95e42b656ab2a26cef61c66f891eb34691a..8b0ce600b38b59fcdc1306b4018aba3e4a2ad827 100644 (file)
--- a/src/cmd/gc/subr.c
+++ b/src/cmd/gc/subr.c
@@ -1539,7 +1539,7 @@ Zconv(Fmt *fp)
                switch(r) {
                case Runeerror:
                        if(n == 1) {
-                               fmtprint(fp, "\\x%02x", *(s-1));
+                               fmtprint(fp, "\\x%02x", (uchar)*(s-1));
                                break;
                        }
                        // fall through