assert sizes of smaller-than-int bit fields in structures

src/common.h

@@ -45,6 +45,10 @@ typedef unsigned long ulong;
 
 #define BIT_ENUM(...)
 
+#define static_assert_bits(pfx, type, field) \
+	static_assert( pfx##__NUM_BITS <= sizeof(((type){ 0 }).field) * 8, \
+	               stringify(type) "::" stringify(field) " is too small" )
+
 #if __GNUC__ > 2 || (__GNUC__ == 2 && __GNUC_MINOR__ > 4)
 # define ATTR_UNUSED __attribute__((unused))
 # define ATTR_NORETURN __attribute__((noreturn))

src/driver.h

@@ -74,6 +74,9 @@ typedef struct message {
 	MESSAGE(struct message)
 } message_t;
 
+static_assert_bits(F, message_t, flags);
+static_assert_bits(M, message_t, status);
+
 // For driver_t->prepare_load_box(), which may amend the passed flags.
 // The drivers don't use the first two, but may set them if loading the
 // particular range is required to handle some other flag; note that these
@@ -108,6 +111,8 @@ typedef struct {
 	uchar flags;
 } msg_data_t;
 
+static_assert_bits(F, msg_data_t, flags);
+
 #define DRV_OK          0
 /* Message went missing, or mailbox is full, etc. */
 #define DRV_MSG_BAD     1

src/sync_p.h

@@ -36,6 +36,9 @@ typedef struct sync_rec {
 	char tuid[TUIDL];
 } sync_rec_t;
 
+static_assert_bits(F, sync_rec_t, flags);
+static_assert_bits(S, sync_rec_t, status);
+
 typedef struct {
 	int t[2];
 	void (*cb)( int sts, void *aux ), *aux;