Implement the D "cpu" variable, which returns curcpu. I have chosen not

to follow the example of OpenSolaris and its descendants, which implemented
cpu as an inline that took a value out of curthread.  At certain points in
the FreeBSD scheduler curthread->td_oncpu will no longer be valid (in
particukar, just before the thread gets descheduled) so instead I have
implemented this as its own built-in variable.

Sponsored by:	Sandvine Inc.
MFC after:	1 week

cddl/contrib/opensolaris/lib/libdtrace/common/dt_open.c

@@ -497,6 +497,12 @@ static const dt_ident_t _dtrace_globals[] = {
 { "zonename", DT_IDENT_SCALAR, 0, DIF_VAR_ZONENAME,
 	DT_ATTR_STABCMN, DT_VERS_1_0, &dt_idops_type, "string" },
 #endif
+
+#if !defined(sun)
+{ "cpu", DT_IDENT_SCALAR, 0, DIF_VAR_CPU,
+	DT_ATTR_STABCMN, DT_VERS_1_6_3, &dt_idops_type, "int" },
+#endif
+
 { NULL, 0, 0, 0, { 0, 0, 0 }, 0, NULL, NULL }
 };
 

sys/cddl/contrib/opensolaris/uts/common/dtrace/dtrace.c

@@ -3143,6 +3143,11 @@ dtrace_dif_variable(dtrace_mstate_t *mstate, dtrace_state_t *state, uint64_t v,
 		return (curthread->td_errno);
 #endif
 	}
+#if !defined(sun)
+	case DIF_VAR_CPU: {
+		return curcpu;
+	}
+#endif
 	default:
 		DTRACE_CPUFLAG_SET(CPU_DTRACE_ILLOP);
 		return (0);

sys/cddl/contrib/opensolaris/uts/common/sys/dtrace.h

@@ -251,6 +251,10 @@ typedef enum dtrace_probespec {
 #define	DIF_VAR_ERRNO		0x0120	/* thread errno */
 #define	DIF_VAR_EXECARGS	0x0121	/* process arguments */
 
+#if !defined(sun)
+#define	DIF_VAR_CPU		0x0200
+#endif
+
 #define	DIF_SUBR_RAND			0
 #define	DIF_SUBR_MUTEX_OWNED		1
 #define	DIF_SUBR_MUTEX_OWNER		2