[libc] Ensure that error numbers from EUNIQ() have the correct type

Error numbers are signed ints.  EUNIQ() should not allow implicit type
promotion based on the supplied error diambiguator, because this
causes problems with statements such as

  rc = ( condition ? -EUNIQ ( EBASE, disambiguator ) : -EBASE );

Signed-off-by: Michael Brown <mcb30@ipxe.org>

diff --git a/src/include/errno.h b/src/include/errno.h
index 45d5382355abc384cb2a0e73a5177ac0378604aa..a86573fc9f9aaf4f4a99fc4568d5e03c0019ebc7 100644 (file)
--- a/src/include/errno.h
+++ b/src/include/errno.h
@@ -201,7 +201,7 @@ extern char missing_errfile_declaration[] __attribute__ (( deprecated ));
  */
 #define EUNIQ( errno, uniq, ... ) ( {                                  \
        euniq_discard ( 0, ##__VA_ARGS__);                              \
-       ( (errno) | ( (uniq) << 8 ) ); } )
+       ( ( int ) ( (errno) | ( (uniq) << 8 ) ) ); } )
 static inline void euniq_discard ( int dummy __unused, ... ) {}
 
 /**