[DTrace-devel] [PATCH v6 7/7] selftests/usdt: add is-enabled stapsdt tests using semaphores

[Kris Van Hees]

This test is flawed because you never initialize the semaphores.  If you change
the code to assign 0 to then, then the test fails because the probes never
fire.  That makes sense because your implementation does not actually do
anything with the semaphore, i.e. if the probe it relatees to is enabled, 
nothing happens to the semaphore, so while you do store the address of the
semaphore in patch 2, it is never used for anything, so this test passing is
actually accidental because the semaphore initial value is (apparently) most
commonly *not* 0.

On Mon, Jul 28, 2025 at 05:36:11PM +0100, Alan Maguire wrote:
> Is-eanbled probes are implemented using semaphores where the
> semaphore address is specified in the ELF notes and passed
> in at probe creation time to have the kernel reference-count
> probes; this allows us to have argument assembly code that
> only gets executed when the stapsdt probe is in use.
> 
> Signed-off-by: Alan Maguire <alan.maguire at oracle.com>
> ---
>  .../usdt/tst.stapsdt-notes-isenabled.r        |  14 ++
>  .../usdt/tst.stapsdt-notes-isenabled.sh       | 151 ++++++++++++++++++
>  2 files changed, 165 insertions(+)
>  create mode 100644 test/unittest/usdt/tst.stapsdt-notes-isenabled.r
>  create mode 100755 test/unittest/usdt/tst.stapsdt-notes-isenabled.sh
> 
> diff --git a/test/unittest/usdt/tst.stapsdt-notes-isenabled.r b/test/unittest/usdt/tst.stapsdt-notes-isenabled.r
> new file mode 100644
> index 00000000..db6d18cb
> --- /dev/null
> +++ b/test/unittest/usdt/tst.stapsdt-notes-isenabled.r
> @@ -0,0 +1,14 @@
> +test:main:zero
> +test:main:one:1
> +test:main:two:2:3
> +test:main:three:4:5:7
> +test:main:four:7:8:9:10
> +test:main:five:11:12:13:14:15
> +test:main:six:16:17:18:19:20:21
> +test:main:seven:22:23:24:25:26:27:28
> +test:main:eight:29:30:31:32:33:34:35:36
> +test:main:nine:37:38:39:40:41:42:43:44:45
> +test:main:ten:46:47:48:49:50:51:52:53:54:55
> +test:main:eleven:56:57:58:59:60:61:62:63:64:65
> +test:main:twelve:67:68:69:70:71:72:73:74:75:76
> +
> diff --git a/test/unittest/usdt/tst.stapsdt-notes-isenabled.sh b/test/unittest/usdt/tst.stapsdt-notes-isenabled.sh
> new file mode 100755
> index 00000000..99fcc844
> --- /dev/null
> +++ b/test/unittest/usdt/tst.stapsdt-notes-isenabled.sh
> @@ -0,0 +1,151 @@
> +#!/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.
> +
> +# This test covers all stapsdt probes fired by the STAP_PROBEn macros.
> +# Arguments values are checked only for first 10 arguments because
> +# there is support for arg0 ... arg9 only at this moment.
> +
> +if [ $# != 1 ]; then
> +	echo expected one argument: '<'dtrace-path'>'
> +	exit 2
> +fi
> +
> +dtrace=$1
> +CC=/usr/bin/gcc
> +CFLAGS="-I${PWD}/test/unittest/usdt"
> +
> +DIRNAME="$tmpdir/usdt-notes.$$.$RANDOM"
> +mkdir -p $DIRNAME
> +cd $DIRNAME
> +
> +cat > test.c <<EOF
> +#define _SDT_HAS_SEMAPHORES 1
> +#include <sdt_notes.h>
> +
> +#define SEC(name) __attribute__((section(name), used))
> +
> +unsigned short test_prov_zero_semaphore SEC(".probes");
> +unsigned short test_prov_one_semaphore SEC(".probes");
> +unsigned short test_prov_two_semaphore SEC(".probes");
> +unsigned short test_prov_three_semaphore SEC(".probes");
> +unsigned short test_prov_four_semaphore SEC(".probes");
> +unsigned short test_prov_five_semaphore SEC(".probes");
> +unsigned short test_prov_six_semaphore SEC(".probes");
> +unsigned short test_prov_seven_semaphore SEC(".probes");
> +unsigned short test_prov_eight_semaphore SEC(".probes");
> +unsigned short test_prov_nine_semaphore SEC(".probes");
> +unsigned short test_prov_ten_semaphore SEC(".probes");
> +unsigned short test_prov_eleven_semaphore SEC(".probes");
> +unsigned short test_prov_twelve_semaphore SEC(".probes");
> +
> +int
> +main(int argc, char **argv)
> +{
> +	if (test_prov_zero_semaphore)
> +		STAP_PROBE(test_prov, zero);
> +	if (test_prov_one_semaphore)
> +		STAP_PROBE1(test_prov, one, argc);
> +	if (test_prov_two_semaphore)
> +		STAP_PROBE2(test_prov, two, 2, 3);
> +	if (test_prov_three_semaphore)
> +		STAP_PROBE3(test_prov, three, 4, 5, 7);
> +	if (test_prov_four_semaphore)
> +		STAP_PROBE4(test_prov, four, 7, 8, 9, 10);
> +	if (test_prov_five_semaphore)
> +		STAP_PROBE5(test_prov, five, 11, 12, 13, 14, 15);
> +	if (test_prov_six_semaphore)
> +		STAP_PROBE6(test_prov, six, 16, 17, 18, 19, 20, 21);
> +	if (test_prov_seven_semaphore)
> +		STAP_PROBE7(test_prov, seven, 22, 23, 24, 25, 26, 27, 28);
> +	if (test_prov_eight_semaphore)
> +		STAP_PROBE8(test_prov, eight, 29, 30, 31, 32, 33, 34, 35, 36);
> +	if (test_prov_nine_semaphore)
> +		STAP_PROBE9(test_prov, nine, 37, 38, 39, 40, 41, 42, 43, 44, 45);
> +	if (test_prov_ten_semaphore)
> +		STAP_PROBE10(test_prov, ten, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55);
> +	if (test_prov_eleven_semaphore)
> +		STAP_PROBE11(test_prov, eleven, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66);
> +	if (test_prov_twelve_semaphore)
> +		STAP_PROBE12(test_prov, twelve, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78);
> +}
> +EOF
> +
> +${CC} ${CFLAGS} -o test test.c
> +if [ $? -ne 0 ]; then
> +	echo "failed to compile test.c" >& 2
> +	exit 1
> +fi
> +
> +$dtrace -c ./test -qs /dev/stdin <<EOF
> +test_prov\$target:::zero
> +{
> +	printf("%s:%s:%s\n", probemod, probefunc, probename);
> +}
> +
> +test_prov\$target:::one
> +{
> +	printf("%s:%s:%s:%li\n", probemod, probefunc, probename, arg0);
> +}
> +
> +test_prov\$target:::two
> +{
> +	printf("%s:%s:%s:%li:%li\n", probemod, probefunc, probename, arg0, arg1);
> +}
> +
> +test_prov\$target:::three
> +{
> +	printf("%s:%s:%s:%li:%li:%li\n", probemod, probefunc, probename, arg0, arg1,
> +	       arg2);
> +}
> +
> +test_prov\$target:::four
> +{
> +	printf("%s:%s:%s:%li:%li:%li:%li\n", probemod, probefunc, probename, arg0, arg1,
> +	       arg2, arg3);
> +}
> +
> +test_prov\$target:::five
> +{
> +	printf("%s:%s:%s:%li:%li:%li:%li:%li\n", probemod, probefunc, probename,
> +	       arg0, arg1, arg2, arg3, arg4);
> +}
> +
> +test_prov\$target:::six
> +{
> +	printf("%s:%s:%s:%li:%li:%li:%li:%li:%li\n", probemod, probefunc, probename,
> +	       arg0, arg1, arg2, arg3, arg4, arg5);
> +}
> +
> +test_prov\$target:::seven
> +{
> +	printf("%s:%s:%s:%li:%li:%li:%li:%li:%li:%li\n", probemod, probefunc, probename,
> +	       arg0, arg1, arg2, arg3, arg4, arg5, arg6);
> +}
> +
> +test_prov\$target:::eight
> +{
> +	printf("%s:%s:%s:%li:%li:%li:%li:%li:%li:%li:%li\n", probemod, probefunc, probename,
> +	       arg0, arg1, arg2, arg3, arg4, arg5, arg6, arg7);
> +}
> +
> +test_prov\$target:::nine
> +{
> +	printf("%s:%s:%s:%li:%li:%li:%li:%li:%li:%li:%li:%li\n", probemod, probefunc, probename,
> +	       arg0, arg1, arg2, arg3, arg4, arg5, arg6, arg7, arg8);
> +}
> +
> +test_prov\$target:::ten,
> +test_prov\$target:::eleven,
> +test_prov\$target:::twelve
> +{
> +	printf("%s:%s:%s:%li:%li:%li:%li:%li:%li:%li:%li:%li:%li\n", probemod, probefunc, probename,
> +	       arg0, arg1, arg2, arg3, arg4, arg5, arg6, arg7, arg8, arg9);
> +}
> +EOF
> +status=$?
> +
> +exit $status
> -- 
> 2.39.3
>