[DTrace-devel] [External] : [PATCH 3/7] test: add pid probe placement test for lld-linked objects

[Eslam Almorshdy via B4 Relay]

From: Eslam Almorshdy <ealmorshdy at d-matrix.ai>

Link the same program with GNU ld and with lld, and check that
pid$target:a.out:target:entry and :return each fire 3 times in both
builds.  Without the previous patch, neither probe fires in the lld
build; the GNU ld build rejects fixes that subtract 0x1000
unconditionally.

Add test/utils/linkers.sh, which lists the linkers $CC can use.  The
test builds with each linker that is installed, and tst.lld-offset.x
skips the test when lld is not installed: no GNU ld option produces
lld's layout.

Assisted-by: Claude Code:claude-opus-5-5
Signed-off-by: Eslam Almorshdy <ealmorshdy at d-matrix.ai>
---
 test/unittest/pid/tst.lld-offset.r  |  1 +
 test/unittest/pid/tst.lld-offset.sh | 59 +++++++++++++++++++++++++++++++++++++
 test/unittest/pid/tst.lld-offset.x  | 14 +++++++++
 test/utils/Build                    |  2 +-
 test/utils/linkers.sh               | 21 +++++++++++++
 5 files changed, 96 insertions(+), 1 deletion(-)

diff --git a/test/unittest/pid/tst.lld-offset.r b/test/unittest/pid/tst.lld-offset.r
new file mode 100644
index 00000000..2e9ba477
--- /dev/null
+++ b/test/unittest/pid/tst.lld-offset.r
@@ -0,0 +1 @@
+success
diff --git a/test/unittest/pid/tst.lld-offset.sh b/test/unittest/pid/tst.lld-offset.sh
new file mode 100755
index 00000000..c2128e32
--- /dev/null
+++ b/test/unittest/pid/tst.lld-offset.sh
@@ -0,0 +1,59 @@
+#!/bin/bash
+#
+# Oracle Linux DTrace.
+# Copyright (c) 2026, 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.
+#
+# Check that pid entry and return probes fire in executables linked by GNU
+# ld and by lld.
+#
+# Uprobes are placed by file offset.  lld's text segment has p_vaddr =
+# p_offset + 0x1000 (x86_64), so an offset computed as the function's
+# distance from the first segment misses the function by 0x1000.
+# The GNU ld build, where the two agree, rejects fixes that subtract 0x1000
+# unconditionally.  Linkers that are not installed are left out; the .x
+# file skips the test if lld is one of them.
+#
+
+dtrace=$1
+utils=$PWD/test/utils
+ncalls=3
+
+DIRNAME=$tmpdir/pid-lld-offset.$$.$RANDOM
+mkdir -p $DIRNAME
+cd $DIRNAME
+
+cat > main.c <<EOF
+volatile int sink;
+
+__attribute__((noinline)) int target(int x) { return x * 2 + 1; }
+
+int main(void)
+{
+	int i;
+
+	for (i = 0; i < $ncalls; i++)
+		sink = target(i);
+	return 0;
+}
+EOF
+
+status=0
+for ld in $($utils/linkers.sh); do
+	$CC -O0 -fuse-ld=$ld -o main-$ld main.c || exit 1
+
+	got=$($dtrace $dt_flags -qn '
+	pid$target:a.out:target:entry, pid$target:a.out:target:return
+	{
+		@[probename] = count();
+	}' -c ./main-$ld 2>&1 | awk 'NF { print $1, $2 }' | sort | paste -sd " ")
+	want="entry $ncalls return $ncalls"
+	if [ "$got" != "$want" ]; then
+		echo "ERROR: main-$ld: got '$got', want '$want'"
+		status=1
+	fi
+done
+
+[ $status -eq 0 ] && echo success
+exit $status
diff --git a/test/unittest/pid/tst.lld-offset.x b/test/unittest/pid/tst.lld-offset.x
new file mode 100755
index 00000000..6a44074d
--- /dev/null
+++ b/test/unittest/pid/tst.lld-offset.x
@@ -0,0 +1,14 @@
+#!/bin/bash
+#
+# Oracle Linux DTrace.
+# Copyright (c) 2026, 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.
+#
+# The layout this test is about is produced only by lld.
+
+if ! test/utils/linkers.sh lld > /dev/null; then
+	echo "ld.lld is not available"
+	exit 2
+fi
+exit 0
diff --git a/test/utils/Build b/test/utils/Build
index 2d97ee30..77d88a34 100644
--- a/test/utils/Build
+++ b/test/utils/Build
@@ -4,7 +4,7 @@
 # http://oss.oracle.com/licenses/upl.
 
 TEST_UTILS = workload_kernel workload_user showUSDT print-stack-layout
-TEST_SCRIPTS = check_result.sh clean_probes.sh cpc_get_events.sh cpc_temp_skip_bug.sh perf_count_event.sh workload_analyze_loop.sh workload_get_iterations.sh get_remote.sh stack_skip_test.sh
+TEST_SCRIPTS = check_result.sh clean_probes.sh cpc_get_events.sh cpc_temp_skip_bug.sh perf_count_event.sh workload_analyze_loop.sh workload_get_iterations.sh get_remote.sh stack_skip_test.sh linkers.sh
 
 define test-util-template
 CMDS += $(1)
diff --git a/test/utils/linkers.sh b/test/utils/linkers.sh
new file mode 100755
index 00000000..5e91ec52
--- /dev/null
+++ b/test/utils/linkers.sh
@@ -0,0 +1,21 @@
+#!/bin/bash
+#
+# Oracle Linux DTrace.
+# Copyright (c) 2026, 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.
+#
+# linkers.sh [LINKER...]: print those of the given linkers (-fuse-ld names;
+# default "bfd lld") that $CC can link a program with.  Fails if none can.
+#
+
+[ $# -eq 0 ] && set -- bfd lld
+
+usable=
+for ld; do
+	echo 'int main(void) { return 0; }' |
+	    ${CC:-gcc} -fuse-ld=$ld -x c -o /dev/null - > /dev/null 2>&1 &&
+	    usable="$usable $ld"
+done
+
+[ -n "$usable" ] && echo $usable

-- 
2.55.0