https://sourceforge.net/p/sdcc/bugs/4070/

Index: sdas/asxxsrc/asexpr.c
===================================================================
--- sdas/asxxsrc/asexpr.c
+++ sdas/asxxsrc/asexpr.c
@@ -863,18 +863,59 @@
 	return((n & s_mask) ? (n | ~v_mask) : (n & v_mask));
 }
 
-/*)Function	void	exprmasks(esp)
+/*)Function	void	exprmasks(n)
  *
  *		int	n		T Line Bytes in Address
  *
  *	The function exprmasks() configures the assembler
- *	for 16, 24, or 32-Bit Data/Addresses.
+ *	for 16, 24, or 32-Bit Data/Addresses.  The arithmetic
+ *	precision follows the address width unless a port
+ *	calls valmasks() afterwards.
  *
  *	local variables:
  *		none
  *
  *	global variables:
  *		int	a_bytes		T Line Bytes in Address
+ *
+ *	functions called:
+ *		void	valmasks()	asexpr.c
+ *
+ *	side effects:
+ *		The address width and arithmetic precision
+ *		parameters are set.
+ */
+
+void
+exprmasks(int n)
+{
+	switch(n) {
+	default:
+		n = 2;
+	case 2:
+	case 3:
+	case 4:
+		break;
+	}
+	a_bytes = n;
+	valmasks(n);
+}
+
+/*)Function	void	valmasks(n)
+ *
+ *		int	n		Bytes of arithmetic precision
+ *
+ *	The function valmasks() configures the 16, 24, or
+ *	32-Bit arithmetic precision independently of the
+ *	T Line address width.  A port whose addresses fit
+ *	in 24 bits but whose symbols may hold 32-bit values
+ *	(the 8051 __sfr32 address lists, for example) uses
+ *	exprmasks(3) followed by valmasks(4).
+ *
+ *	local variables:
+ *		none
+ *
+ *	global variables:
  *		a_uint	a_mask		Address mask
  *		a_uint	s_mask		Sign mask
  *		a_uint	v_mask		Value mask
@@ -885,16 +926,13 @@
  *	side effects:
  *		The arithmetic precision parameters are set.
  */
- 
+
 void
-exprmasks(int n)
+valmasks(int n)
 {
-	a_bytes = n;
-
 #ifdef	LONGINT
-	switch(a_bytes) {
+	switch(n) {
 	default:
-		a_bytes = 2;
 	case 2:
 		a_mask = (a_uint) 0x0000FFFFl;
 		s_mask = (a_uint) 0x00008000l;
@@ -914,9 +952,8 @@
 		break;
 	}
 #else
-	switch(a_bytes) {
+	switch(n) {
 	default:
-		a_bytes = 2;
 	case 2:
 		a_mask = (a_uint) 0x0000FFFF;
 		s_mask = (a_uint) 0x00008000;
Index: sdas/asxxsrc/asxxxx.h
===================================================================
--- sdas/asxxsrc/asxxxx.h
+++ sdas/asxxsrc/asxxxx.h
@@ -1354,6 +1354,7 @@
 extern	int		digit(int c, int r);
 extern	int		is_digit(int c, int r);
 extern	void		exprmasks(int n);
+extern	void		valmasks(int n);
 extern	void		expr(struct expr *esp, int n);
 extern	void		binop(int c, struct expr *esp, struct expr *re);
 extern	int		is_abs(struct expr *esp);
Index: sdas/as8051/i51mch.c
===================================================================
--- sdas/as8051/i51mch.c
+++ sdas/as8051/i51mch.c
@@ -782,9 +782,12 @@
 	hilo = 1;
 
 	/*
-         * Address Space
+	 * Address Space: 24-bit addresses in the T lines,
+	 * 32-bit arithmetic so that __sfr32 address lists
+	 * like 0xa4a5a6a7 keep their most significant byte.
 	 */
-        exprmasks(3);
+	exprmasks(3);
+	valmasks(4);
 
 	/*
 	 * First time only: