--- pmc.h	(revision 214857)
+++ pmc.h	(local)
@@ -584,11 +584,30 @@
  * PMC commands
  */
 
+#define	PAD_(t)	(sizeof(register_t) <= sizeof(t) ? \
+		0 : sizeof(register_t) - sizeof(t))
+
+#if BYTE_ORDER == LITTLE_ENDIAN
+#define	PADL_(t)	0
+#define	PADR_(t)	PAD_(t)
+#else
+#define	PADL_(t)	PAD_(t)
+#define	PADR_(t)	0
+#endif
+
 struct pmc_syscall_args {
+	char		code_l_[PADL_(uint32_t)];
 	uint32_t	pmop_code;	/* one of PMC_OP_* */
+	char		code_r_[PADR_(uint32_t)];
+	char		data_l_[PADL_(void*)];
 	void		*pmop_data;	/* syscall parameter */
+	char		data_r_[PADR_(void*)];
 };
 
+#undef PAD_
+#undef PADL_
+#undef PADR_
+
 /*
  * Interface to processor specific s1tuff
  */