Index: usr.bin/truss/syscall.h
===================================================================
--- usr.bin/truss/syscall.h
+++ usr.bin/truss/syscall.h
@@ -40,6 +40,7 @@
  * Int -- normal integer values (file descriptors, for example)
  * LongHex -- long value that should be printed in hex
  * Name -- pointer to a NULL-terminated string.
+ * ShmName -- pointer to a NULL-terminated string, or shm_open's SHM_ANON.
  * BinString -- pointer to an array of chars, printed via strvisx().
  * Ptr -- pointer to some unspecified structure.  Just print as hex for now.
  * Stat -- a pointer to a stat buffer.  Prints a couple fields.
@@ -146,6 +147,7 @@
 	IntArray,
 	Iovec,
 	Name,
+	ShmName,
 	PipeFds,
 	PSig,
 	PQuadHex,
Index: usr.bin/truss/syscalls.c
===================================================================
--- usr.bin/truss/syscalls.c
+++ usr.bin/truss/syscalls.c
@@ -44,6 +44,7 @@
 #define	_WANT_FREEBSD11_KEVENT
 #include <sys/event.h>
 #include <sys/ioccom.h>
+#include <sys/mman.h>
 #include <sys/mount.h>
 #include <sys/ptrace.h>
 #include <sys/resource.h>
@@ -462,7 +463,7 @@
 	  .args = { { Int, 0 }, { Sockoptlevel, 1 }, { Sockoptname, 2 },
 		    { Ptr | IN, 3 }, { Socklent, 4 } } },
 	{ .name = "shm_open", .ret_type = 1, .nargs = 3,
-	  .args = { { Name | IN, 0 }, { Open, 1 }, { Octal, 2 } } },
+	  .args = { { ShmName | IN, 0 }, { Open, 1 }, { Octal, 2 } } },
 	{ .name = "shm_unlink", .ret_type = 1, .nargs = 1,
 	  .args = { { Name | IN, 0 } } },
 	{ .name = "shutdown", .ret_type = 1, .nargs = 2,
@@ -1593,6 +1594,13 @@
 	case Sizet:
 		fprintf(fp, "%zu", (size_t)args[sc->offset]);
 		break;
+	case ShmName:
+		/* Handle special SHM_ANON value. */
+		if ((char *) args[sc->offset] == SHM_ANON) {
+			fprintf(fp, "SHM_ANON");
+			break;
+		}
+		/* Otherwise fall through and display as regular Name. */
 	case Name: {
 		/* NULL-terminated string. */
 		char *tmp2;