provider: change the trampoline return type

The trampoline callback can now return 1 to indicate that no calls
should be made to clause functions (or 0 to retain the regular
operation of calling the clause functions).

This will be used by some providers to attach to probes that perform
auxiliary operations, e.g. setting up some data items that will be
needed for the actual probe processing.

Signed-off-by: Kris Van Hees <kris.van.hees@oracle.com>
Reviewed-by: Eugene Loh <eugene.loh@oracle.com>

libdtrace/dt_cg.c

@@ -590,13 +590,16 @@ dt_cg_add_dependent(dtrace_hdl_t *dtp, dt_probe_t *prp, void *arg)
 	dt_ident_t	*idp = dt_dlib_add_probe_var(pcb->pcb_hdl, prp);
 	dt_probe_t	*saved_prp = pcb->pcb_probe;
 	uint_t		exitlbl = dt_irlist_label(dlp);
+	int		skip = 0;
 
 	dt_cg_tramp_save_args(pcb);
 	pcb->pcb_probe = prp;
 	emite(dlp, BPF_STORE_IMM(BPF_W, BPF_REG_7, DMST_PRID, prp->desc->id), idp);
 	if (prp->prov->impl->trampoline != NULL)
-		prp->prov->impl->trampoline(pcb, exitlbl);
-	dt_cg_tramp_call_clauses(pcb, prp, DT_ACTIVITY_ACTIVE);
+		skip = prp->prov->impl->trampoline(pcb, exitlbl);
+
+	if (!skip)
+		dt_cg_tramp_call_clauses(pcb, prp, DT_ACTIVITY_ACTIVE);
 
 	pcb->pcb_probe = saved_prp;
 	dt_cg_tramp_restore_args(pcb);

libdtrace/dt_prov_cpc.c

@@ -383,7 +383,7 @@ static int provide(dtrace_hdl_t *dtp, const dtrace_probedesc_t *pdp)
  *         __u64 addr;
  *     }
  */
-static void trampoline(dt_pcb_t *pcb, uint_t exitlbl)
+static int trampoline(dt_pcb_t *pcb, uint_t exitlbl)
 {
 	int		i;
 	dt_irlist_t	*dlp = &pcb->pcb_ir;
@@ -406,6 +406,8 @@ static void trampoline(dt_pcb_t *pcb, uint_t exitlbl)
 		emit(dlp, BPF_STORE_IMM(BPF_DW, BPF_REG_7, DMST_ARG(i), 0));
 
 	dt_cg_tramp_epilogue(pcb);
+
+	return 0;
 }
 
 static int attach(dtrace_hdl_t *dtp, const dt_probe_t *prp, int bpf_fd)

libdtrace/dt_prov_dtrace.c

@@ -1,6 +1,6 @@
 /*
  * Oracle Linux DTrace.
- * Copyright (c) 2019, 2022, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2019, 2023, Oracle and/or its affiliates. All rights reserved.
  * Licensed under the Universal Permissive License v 1.0 as shown at
  * http://oss.oracle.com/licenses/upl.
  *
@@ -77,7 +77,7 @@ static int populate(dtrace_hdl_t *dtp)
  * The trampoline will populate a dt_dctx_t struct and then call the function
  * that implements the compiled D clause.  It returns 0 to the caller.
  */
-static void trampoline(dt_pcb_t *pcb, uint_t exitlbl)
+static int trampoline(dt_pcb_t *pcb, uint_t exitlbl)
 {
 	dt_irlist_t	*dlp = &pcb->pcb_ir;
 	dt_activity_t	act = DT_ACTIVITY_ACTIVE;
@@ -90,7 +90,7 @@ static void trampoline(dt_pcb_t *pcb, uint_t exitlbl)
 	 */
 	if (strcmp(pcb->pcb_probe->desc->prb, "ERROR") == 0) {
 		dt_cg_tramp_error(pcb);
-		return;
+		return 0;
 	}
 
 	/*
@@ -163,6 +163,8 @@ static void trampoline(dt_pcb_t *pcb, uint_t exitlbl)
 		emit(dlp, BPF_STORE_IMM(BPF_DW, BPF_REG_7, DMST_ARG(i), 0));
 
 	dt_cg_tramp_epilogue_advance(pcb, act);
+
+	return 0;
 }
 
 static char *uprobe_spec(const char *prb)

libdtrace/dt_prov_fbt.c

@@ -152,7 +152,7 @@ static int populate(dtrace_hdl_t *dtp)
  * The trampoline will populate a dt_dctx_t struct and then call the function
  * that implements the compiled D clause.  It returns 0 to the caller.
  */
-static void trampoline(dt_pcb_t *pcb, uint_t exitlbl)
+static int trampoline(dt_pcb_t *pcb, uint_t exitlbl)
 {
 	dt_cg_tramp_prologue(pcb);
 
@@ -181,6 +181,8 @@ static void trampoline(dt_pcb_t *pcb, uint_t exitlbl)
 	} else
 		dt_cg_tramp_copy_args_from_regs(pcb, 1);
 	dt_cg_tramp_epilogue(pcb);
+
+	return 0;
 }
 
 static int attach(dtrace_hdl_t *dtp, const dt_probe_t *prp, int bpf_fd)

libdtrace/dt_prov_proc.c

@@ -298,7 +298,7 @@ static void enable(dtrace_hdl_t *dtp, dt_probe_t *prp)
  * that implements the compiled D clause.  It returns the value that it gets
  * back from that function.
  */
-static void trampoline(dt_pcb_t *pcb, uint_t exitlbl)
+static int trampoline(dt_pcb_t *pcb, uint_t exitlbl)
 {
 	dtrace_hdl_t	*dtp = pcb->pcb_hdl;
 	dt_irlist_t	*dlp = &pcb->pcb_ir;
@@ -388,6 +388,8 @@ static void trampoline(dt_pcb_t *pcb, uint_t exitlbl)
 		emit(dlp, BPF_STORE(BPF_DW, BPF_REG_7, DMST_ARG(0), BPF_REG_0));
 		emit(dlp, BPF_STORE(BPF_DW, BPF_REG_7, DMST_ARG(1), BPF_REG_1));
 	}
+
+	return 0;
 }
 
 static int probe_info(dtrace_hdl_t *dtp, const dt_probe_t *prp,

libdtrace/dt_prov_profile.c

@@ -213,7 +213,7 @@ static int provide(dtrace_hdl_t *dtp, const dtrace_probedesc_t *pdp)
  *         __u64 addr;
  *     }
  */
-static void trampoline(dt_pcb_t *pcb, uint_t exitlbl)
+static int trampoline(dt_pcb_t *pcb, uint_t exitlbl)
 {
 	int		i;
 	dt_irlist_t	*dlp = &pcb->pcb_ir;
@@ -252,6 +252,8 @@ static void trampoline(dt_pcb_t *pcb, uint_t exitlbl)
 		emit(dlp, BPF_STORE_IMM(BPF_DW, BPF_REG_7, DMST_ARG(i), 0));
 
 	dt_cg_tramp_epilogue(pcb);
+
+	return 0;
 }
 
 static int attach(dtrace_hdl_t *dtp, const dt_probe_t *prp, int bpf_fd)

libdtrace/dt_prov_rawtp.c

@@ -1,6 +1,6 @@
 /*
  * Oracle Linux DTrace.
- * Copyright (c) 2019, 2022, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2019, 2023, Oracle and/or its affiliates. All rights reserved.
  * Licensed under the Universal Permissive License v 1.0 as shown at
  * http://oss.oracle.com/licenses/upl.
  *
@@ -131,7 +131,7 @@ static int populate(dtrace_hdl_t *dtp)
  * that implements the compiled D clause.  It returns the value that it gets
  * back from that function.
  */
-static void trampoline(dt_pcb_t *pcb, uint_t exitlbl)
+static int trampoline(dt_pcb_t *pcb, uint_t exitlbl)
 {
 	int		i;
 	dt_irlist_t	*dlp = &pcb->pcb_ir;
@@ -153,6 +153,8 @@ static void trampoline(dt_pcb_t *pcb, uint_t exitlbl)
 	}
 
 	dt_cg_tramp_epilogue(pcb);
+
+	return 0;
 }
 
 static int probe_info(dtrace_hdl_t *dtp, const dt_probe_t *prp,

libdtrace/dt_prov_sdt.c

@@ -1,6 +1,6 @@
 /*
  * Oracle Linux DTrace.
- * Copyright (c) 2019, 2022, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2019, 2023, Oracle and/or its affiliates. All rights reserved.
  * Licensed under the Universal Permissive License v 1.0 as shown at
  * http://oss.oracle.com/licenses/upl.
  *
@@ -128,7 +128,7 @@ static int populate(dtrace_hdl_t *dtp)
  * that implements the compiled D clause.  It returns the value that it gets
  * back from that function.
  */
-static void trampoline(dt_pcb_t *pcb, uint_t exitlbl)
+static int trampoline(dt_pcb_t *pcb, uint_t exitlbl)
 {
 	int		i;
 	dt_irlist_t	*dlp = &pcb->pcb_ir;
@@ -182,6 +182,8 @@ static void trampoline(dt_pcb_t *pcb, uint_t exitlbl)
 		emit(dlp, BPF_STORE_IMM(BPF_DW, BPF_REG_7, DMST_ARG(i), 0));
 
 	dt_cg_tramp_epilogue(pcb);
+
+	return 0;
 }
 
 static int probe_info(dtrace_hdl_t *dtp, const dt_probe_t *prp,

libdtrace/dt_prov_syscall.c

@@ -1,6 +1,6 @@
 /*
  * Oracle Linux DTrace.
- * Copyright (c) 2019, 2022, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2019, 2023, Oracle and/or its affiliates. All rights reserved.
  * Licensed under the Universal Permissive License v 1.0 as shown at
  * http://oss.oracle.com/licenses/upl.
  *
@@ -131,7 +131,7 @@ static int populate(dtrace_hdl_t *dtp)
  * The trampoline will populate a dt_dctx_t struct and then call the function
  * that implements the compiled D clause.  It returns 0 to the caller.
  */
-static void trampoline(dt_pcb_t *pcb, uint_t exitlbl)
+static int trampoline(dt_pcb_t *pcb, uint_t exitlbl)
 {
 	int		i;
 	dt_irlist_t	*dlp = &pcb->pcb_ir;
@@ -188,6 +188,8 @@ static void trampoline(dt_pcb_t *pcb, uint_t exitlbl)
 	}
 
 	dt_cg_tramp_epilogue(pcb);
+
+	return 0;
 }
 
 static int probe_info(dtrace_hdl_t *dtp, const dt_probe_t *prp,

libdtrace/dt_prov_uprobe.c

@@ -391,7 +391,7 @@ static void enable_usdt(dtrace_hdl_t *dtp, dt_probe_t *prp)
  * The trampoline will first populate a dt_dctx_t struct.  It will then emulate
  * the firing of all dependent pid* probes and their clauses.
  */
-static void trampoline(dt_pcb_t *pcb, uint_t exitlbl)
+static int trampoline(dt_pcb_t *pcb, uint_t exitlbl)
 {
 	dt_irlist_t		*dlp = &pcb->pcb_ir;
 	const dt_probe_t	*prp = pcb->pcb_probe;
@@ -465,6 +465,8 @@ static void trampoline(dt_pcb_t *pcb, uint_t exitlbl)
 	}
 
 	dt_cg_tramp_return(pcb);
+
+	return 0;
 }
 
 /*
@@ -503,7 +505,7 @@ copyout_val(dt_pcb_t *pcb, uint_t lbl, uint32_t val, int arg)
  * The trampoline dereferences the passed-in arg and writes 1 into it if this is
  * one of the processes for which the probe is enabled.
  */
-static void trampoline_is_enabled(dt_pcb_t *pcb, uint_t exitlbl)
+static int trampoline_is_enabled(dt_pcb_t *pcb, uint_t exitlbl)
 {
 	dt_irlist_t		*dlp = &pcb->pcb_ir;
 	const dt_probe_t	*prp = pcb->pcb_probe;
@@ -579,6 +581,8 @@ static void trampoline_is_enabled(dt_pcb_t *pcb, uint_t exitlbl)
 	copyout_val(pcb, lbl_assign, 1, 0);
 
 	dt_cg_tramp_return(pcb);
+
+	return 0;
 }
 
 static int attach(dtrace_hdl_t *dtp, const dt_probe_t *prp, int bpf_fd)

libdtrace/dt_provider.h

@@ -63,7 +63,7 @@ typedef struct dt_provimpl {
 		       const pid_probespec_t *psp);
 	void (*enable)(dtrace_hdl_t *dtp,	/* enable the given probe */
 		       struct dt_probe *prp);
-	void (*trampoline)(dt_pcb_t *pcb,	/* generate BPF trampoline */
+	int (*trampoline)(dt_pcb_t *pcb,	/* generate BPF trampoline */
 			   uint_t exitlbl);
 	int (*attach)(dtrace_hdl_t *dtp,	/* attach BPF prog to probe */
 		      const struct dt_probe *prp, int bpf_fd);