diff --git a/sys/cddl/contrib/opensolaris/uts/common/sys/dtrace.h b/sys/cddl/contrib/opensolaris/uts/common/sys/dtrace.h
--- a/sys/cddl/contrib/opensolaris/uts/common/sys/dtrace.h
+++ b/sys/cddl/contrib/opensolaris/uts/common/sys/dtrace.h
@@ -51,6 +51,12 @@
 
 #include <sys/param.h>
 #include <sys/stdint.h>
+#include <sys/types.h>
+
+#if defined(__i386) || defined(__amd64) || defined (__riscv)
+extern int dtrace_instr_size(uint8_t *instr);
+#endif
+
 #ifdef _KERNEL
 #include <sys/endian.h>
 #endif
@@ -71,7 +77,6 @@
 #include <sys/ioccom.h>
 #include <sys/cred.h>
 #include <sys/proc.h>
-#include <sys/types.h>
 #include <sys/ucred.h>
 #endif
 typedef int model_t;
@@ -2399,8 +2404,7 @@
 extern int dtrace_mach_aframes(void);
 
 #if defined(__i386) || defined(__amd64)
-extern int dtrace_instr_size(uchar_t *instr);
-extern int dtrace_instr_size_isa(uchar_t *, model_t, int *);
+extern int dtrace_instr_size_isa(uint8_t *, model_t, int *);
 extern void dtrace_invop_callsite(void);
 #endif
 extern void dtrace_invop_add(int (*)(uintptr_t, struct trapframe *, uintptr_t));
diff --git a/sys/cddl/dev/dtrace/riscv/instr_size.c b/sys/cddl/dev/dtrace/riscv/instr_size.c
new file mode 100644
--- /dev/null
+++ b/sys/cddl/dev/dtrace/riscv/instr_size.c
@@ -0,0 +1,21 @@
+/*
+ * SPDX-License-Identifier: CDDL 1.0
+ *
+ * Copyright 2023 Christos Margiolis <christos@FreeBSD.org>
+ */
+
+#include <machine/encoding.h>
+
+#include <dtrace.h>
+
+#define RVC_MASK 0x03
+
+int
+dtrace_instr_size(uint8_t *instr)
+{
+	/* Detect compressed instructions. */
+	if ((~(*instr) & RVC_MASK) == 0)
+		return (INSN_SIZE);
+	else
+		return (INSN_C_SIZE);
+}
diff --git a/sys/cddl/dev/dtrace/x86/instr_size.c b/sys/cddl/dev/dtrace/x86/instr_size.c
--- a/sys/cddl/dev/dtrace/x86/instr_size.c
+++ b/sys/cddl/dev/dtrace/x86/instr_size.c
@@ -49,8 +49,8 @@
 
 typedef	u_int			model_t;
 #define	DATAMODEL_NATIVE	0
-int dtrace_instr_size(uchar_t *);
-int dtrace_instr_size_isa(uchar_t *, model_t, int *);
+int dtrace_instr_size(uint8_t *);
+int dtrace_instr_size_isa(uint8_t *, model_t, int *);
 #endif
 
 #include <dis_tables.h>
@@ -83,7 +83,7 @@
 dtrace_dis_get_byte(void *p)
 {
 	int ret;
-	uchar_t **instr = p;
+	uint8_t **instr = p;
 
 	ret = **instr;
 	*instr += 1;
@@ -101,7 +101,7 @@
  */
 /* ARGSUSED2 */
 static int
-dtrace_dis_isize(uchar_t *instr, dis_isize_t which, model_t model, int *rmindex)
+dtrace_dis_isize(uint8_t *instr, dis_isize_t which, model_t model, int *rmindex)
 {
 	int sz;
 	dis86_t	x;
@@ -127,13 +127,13 @@
 }
 
 int
-dtrace_instr_size_isa(uchar_t *instr, model_t model, int *rmindex)
+dtrace_instr_size_isa(uint8_t *instr, model_t model, int *rmindex)
 {
 	return (dtrace_dis_isize(instr, DIS_ISIZE_INSTR, model, rmindex));
 }
 
 int
-dtrace_instr_size(uchar_t *instr)
+dtrace_instr_size(uint8_t *instr)
 {
 	return (dtrace_dis_isize(instr, DIS_ISIZE_INSTR, DATAMODEL_NATIVE,
 	    NULL));