Use unsigned as base type for some enums

-fsanitize=undefined complains about using operator~ on various enum
types that are used with DEF_ENUM_FLAGS_TYPE.  This patch fixes these
problems by explicitly setting the base type for these enums to
unsigned.  It also adds a static assert to enum_flags to ensure that
future enums used this way have an unsigned underlying type.

gdb/ChangeLog
2018-10-03  Tom Tromey  <tom@tromey.com>

	* common/enum-flags.h (enum_flags::operator~): Add static assert.
	* symfile-add-flags.h (enum symfile_add_flag): Use unsigned as
	base type.
	* objfile-flags.h (enum objfile_flag): Use unsigned as base type.
	* gdbtypes.h (enum type_instance_flag_value): Use unsigned as base
	type.
	* c-lang.h (enum c_string_type_values): Use unsigned as base
	type.
	* btrace.h (enum btrace_thread_flag): Use unsigned as base type.

1 files changed, 6 insertions, 0 deletions

diff --git a/gdb/common/enum-flags.h b/gdb/common/enum-flags.h
index 82568a5..f7ca8d8 100644
--- a/gdb/common/enum-flags.h
+++ b/gdb/common/enum-flags.h
@@ -164,6 +164,12 @@ public:
   }
   enum_flags operator~ () const
   {
+    // We only the underlying type to be unsigned when actually using
+    // operator~ -- if it were not unsigned, undefined behavior could
+    // result.  However, asserting this in the class itself would
+    // require too many unnecessary changes to otherwise ok enum
+    // types.
+    gdb_static_assert (std::is_unsigned<underlying_type>::value);
     return (enum_type) ~underlying_value ();
   }