[DTrace-devel] [PATCH v2 05/22] Set the ERROR PRID in BPF code

[eugene.loh at oracle.com]

From: Eugene Loh <eugene.loh at oracle.com>

There are multiple options for how to set this value.  One is to
hardwire it to 3, its expected value.  Another is to set the value
during relocation.  Here, we choose a middle ground:  we define
the value symbolically (to 3) and also check that value.

Signed-off-by: Eugene Loh <eugene.loh at oracle.com>
---
 bpf/probe_error.c                        |  3 ++
 libdtrace/dt_dctx.h                      |  7 ++++
 libdtrace/dt_prov_dtrace.c               |  3 ++
 test/unittest/builtinvar/tst.id_ERROR.r  |  1 +
 test/unittest/builtinvar/tst.id_ERROR.sh | 52 ++++++++++++++++++++++++
 5 files changed, 66 insertions(+)
 create mode 100644 test/unittest/builtinvar/tst.id_ERROR.r
 create mode 100755 test/unittest/builtinvar/tst.id_ERROR.sh

diff --git a/bpf/probe_error.c b/bpf/probe_error.c
index cad161fd7..1081ee71d 100644
--- a/bpf/probe_error.c
+++ b/bpf/probe_error.c
@@ -26,6 +26,7 @@ noinline void dt_probe_error(const dt_dctx_t *dctx, uint64_t pc, uint64_t fault,
 			     uint64_t illval)
 {
 	dt_mstate_t	*mst = dctx->mst;
+	int		oldprid = mst->prid;
 
 	__builtin_memcpy(mst->saved_argv, mst->argv, sizeof(mst->saved_argv));
 	mst->argv[0] = 0;
@@ -35,7 +36,9 @@ noinline void dt_probe_error(const dt_dctx_t *dctx, uint64_t pc, uint64_t fault,
 	mst->argv[4] = fault;
 	mst->argv[5] = illval;
 
+	mst->prid = DTRACE_ERROR_ID;
 	dt_error(dctx);
+	mst->prid = oldprid;
 
 	__builtin_memcpy(mst->argv, mst->saved_argv, sizeof(mst->saved_argv));
 	mst->fault = fault;
diff --git a/libdtrace/dt_dctx.h b/libdtrace/dt_dctx.h
index 633c529f3..d8232868d 100644
--- a/libdtrace/dt_dctx.h
+++ b/libdtrace/dt_dctx.h
@@ -14,6 +14,13 @@
 #include <dt_pt_regs.h>
 #include <dt_state.h>
 
+/*
+ * Static probe IDs for the dtrace provider.
+ */
+#define DTRACE_BEGIN_ID		1
+#define DTRACE_END_ID		2
+#define DTRACE_ERROR_ID		3
+
 /*
  * The DTrace machine state.
  */
diff --git a/libdtrace/dt_prov_dtrace.c b/libdtrace/dt_prov_dtrace.c
index bf87cb054..9f0d72b78 100644
--- a/libdtrace/dt_prov_dtrace.c
+++ b/libdtrace/dt_prov_dtrace.c
@@ -45,18 +45,21 @@ static int populate(dtrace_hdl_t *dtp)
 
 	prp = dt_tp_probe_insert(dtp, prv, prvname, modname, funname, "BEGIN");
 	if (prp) {
+		assert(prp->desc->id == DTRACE_BEGIN_ID);
 		n++;
 		dt_probe_enable(dtp, prp);
 	}
 
 	prp = dt_tp_probe_insert(dtp, prv, prvname, modname, funname, "END");
 	if (prp) {
+		assert(prp->desc->id == DTRACE_END_ID);
 		n++;
 		dt_probe_enable(dtp, prp);
 	}
 
 	prp = dt_tp_probe_insert(dtp, prv, prvname, modname, funname, "ERROR");
 	if (prp) {
+		assert(prp->desc->id == DTRACE_ERROR_ID);
 		n++;
 		dt_probe_enable(dtp, prp);
 		dtp->dt_error = prp;
diff --git a/test/unittest/builtinvar/tst.id_ERROR.r b/test/unittest/builtinvar/tst.id_ERROR.r
new file mode 100644
index 000000000..2e9ba477f
--- /dev/null
+++ b/test/unittest/builtinvar/tst.id_ERROR.r
@@ -0,0 +1 @@
+success
diff --git a/test/unittest/builtinvar/tst.id_ERROR.sh b/test/unittest/builtinvar/tst.id_ERROR.sh
new file mode 100755
index 000000000..082ebd0c4
--- /dev/null
+++ b/test/unittest/builtinvar/tst.id_ERROR.sh
@@ -0,0 +1,52 @@
+#!/bin/bash
+#
+# Oracle Linux DTrace.
+# Copyright (c) 2024, 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.
+#
+
+dtrace=$1
+
+DIRNAME="$tmpdir/builtinvar-id_ERROR.$$.$RANDOM"
+mkdir -p $DIRNAME
+cd $DIRNAME
+
+# Have a D script report the probe ID within an ERROR probe.
+
+$dtrace $dt_flags -qn '
+BEGIN { *((int*)0) }
+BEGIN { exit(1) }
+ERROR { printf("ERROR probe id is %d\n", id); exit(0); }
+' -o D.out 2> D.err
+if [ $? -ne 0 ]; then
+    echo DTrace failed
+    echo ==== D.out
+    cat D.out
+    echo ==== D.err
+    cat D.err
+    exit 1
+fi
+
+# Get the ERROR probe ID from "dtrace -l" output.
+
+id=`$dtrace $dt_flags -ln dtrace:::ERROR |& awk '/^ *[0-9]* *dtrace *ERROR *$/ { print $1 }'`
+
+# Construct expected output.
+
+echo "ERROR probe id is $id" > D.out.chk
+echo >> D.out.chk
+
+# Check output.
+
+if ! diff -q D.out D.out.chk; then
+    echo output mismatches
+    echo ==== D.out
+    cat D.out
+    echo ==== D.out.chk
+    cat D.out.chk
+    exit 1
+fi
+
+echo success
+exit 0
-- 
2.43.5