Avoid undefined behavior in argp-parse.cQtCreator4.6.2QtCreator4.6.0-rc1QtCreator4.6.0-beta1QtCreator4.6.04.6

The shifting-instead-of-masking trick outlined there is very clever, but
only works incidentally. Explicitly preserve the sign, and still shift,
but shift unsigned values for which left-shifting bits out is defined.

make distcheck complains about the previous code with sufficiently
recent compilers with UB sanitizers.

Change-Id: I6f2942f307a2c154ea7d414a85c60e4f088fc918
Reviewed-by: Christian Kandeler <christian.kandeler@qt.io>

1 files changed, 9 insertions, 6 deletions

diff --git a/libgnu/argp-parse.c b/libgnu/argp-parse.c
index 3f723bc8..dc3106e7 100644
--- a/libgnu/argp-parse.c
+++ b/libgnu/argp-parse.c
@@ -740,12 +740,15 @@ parser_parse_opt (struct parser *parser, int opt, char *val)
             }
     }
   else
-    /* A long option.  We use shifts instead of masking for extracting
-       the user value in order to preserve the sign.  */
-    err =
-      group_parse (&parser->groups[group_key - 1], &parser->state,
-                   (opt << GROUP_BITS) >> GROUP_BITS,
-                   parser->opt_data.optarg);
+    {
+      uint maskable = (uint)(opt < 0 ? -opt : opt);
+      maskable = (maskable << GROUP_BITS) >> GROUP_BITS;
+      int masked = opt < 0 ? -(int)maskable : (int)maskable;
+
+      err =
+        group_parse (&parser->groups[group_key - 1], &parser->state,
+                     masked, parser->opt_data.optarg);
+    }
 
   if (err == EBADKEY)
     /* At least currently, an option not recognized is an error in the