[DTrace-devel] [PATCH] Add function name to underlying return probes

[Kris Van Hees]

On Tue, Aug 05, 2025 at 12:51:11AM -0400, eugene.loh--- via DTrace-devel wrote:
> From: Eugene Loh <eugene.loh at oracle.com>
> 
> In commit 35a4f05c2
> ("Add support for pid function "-" with absolute offset"),
> function names were removed from underlying probe descriptions.
> That was so that pid absolute offset probes (pid$pid:a.out:-:$absoff),
> with function "-", could sit on the same underlying probes as
> pid$pid:$mod:$fun:entry, pid$pid:$mod:$fun:$off, and USDT probes.
> 
> While that made sense for those probes, it did not make sense for pid
> return probes:  their underlying probes, all with probe name "return",
> are no longer distinguishable.  Further, there was no need for any such
> change, since no other probes will have the same underlying return probe.
> 
> Name underlying return probes with function name.
> 
> Signed-off-by: Eugene Loh <eugene.loh at oracle.com>

Reviewed-by: Kris Van Hees <kris.van.hees at oracle.com>

> ---
>  libdtrace/dt_prov_uprobe.c           |  7 +++++--
>  test/unittest/pid/tst.multi-return.d | 21 +++++++++++++++++++++
>  test/unittest/pid/tst.multi-return.r |  7 +++++++
>  3 files changed, 33 insertions(+), 2 deletions(-)
>  create mode 100644 test/unittest/pid/tst.multi-return.d
>  create mode 100644 test/unittest/pid/tst.multi-return.r
> 
> diff --git a/libdtrace/dt_prov_uprobe.c b/libdtrace/dt_prov_uprobe.c
> index a633b6fe7..3661f09d9 100644
> --- a/libdtrace/dt_prov_uprobe.c
> +++ b/libdtrace/dt_prov_uprobe.c
> @@ -906,6 +906,7 @@ static dt_probe_t *create_underlying(dtrace_hdl_t *dtp,
>  				     const pid_probespec_t *psp)
>  {
>  	char			mod[DTRACE_MODNAMELEN];
> +	char			fun[DTRACE_FUNCNAMELEN];
>  	char			prb[DTRACE_NAMELEN];
>  	dtrace_probedesc_t	pd;
>  	dt_probe_t		*uprp;
> @@ -923,12 +924,14 @@ static dt_probe_t *create_underlying(dtrace_hdl_t *dtp,
>  	 *
>  	 * The probe description for return probes is:
>  	 *
> -	 *	uprobe:<dev>_<inode>::return
> +	 *	uprobe:<dev>_<inode>:<func>:return
>  	 */
>  	snprintf(mod, sizeof(mod), "%lx_%lx", psp->pps_dev, psp->pps_inum);
>  
> +	fun[0] = '\0';
>  	switch (psp->pps_type) {
>  	case DTPPT_RETURN:
> +		strcpy(fun, psp->pps_fun);
>  		strcpy(prb, "return");
>  		break;
>  	case DTPPT_IS_ENABLED:
> @@ -946,7 +949,7 @@ static dt_probe_t *create_underlying(dtrace_hdl_t *dtp,
>  	pd.id = DTRACE_IDNONE;
>  	pd.prv = prvname;
>  	pd.mod = mod;
> -	pd.fun = "";
> +	pd.fun = fun;
>  	pd.prb = prb;
>  
>  	dt_dprintf("Providing underlying probe %s:%s:%s:%s @ %lx\n", psp->pps_prv,
> diff --git a/test/unittest/pid/tst.multi-return.d b/test/unittest/pid/tst.multi-return.d
> new file mode 100644
> index 000000000..0f81f343c
> --- /dev/null
> +++ b/test/unittest/pid/tst.multi-return.d
> @@ -0,0 +1,21 @@
> +/*
> + * Oracle Linux DTrace.
> + * Copyright (c) 2025, 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.
> + */
> +
> +/* @@trigger: profile-tst-ufuncsort */
> +/* @@nosort */
> +
> +#pragma D option quiet
> +
> +pid$target:a.out::return
> +{
> +	@[probefunc] = count();
> +}
> +
> +tick-2s
> +{
> +	exit(0);
> +}
> diff --git a/test/unittest/pid/tst.multi-return.r b/test/unittest/pid/tst.multi-return.r
> new file mode 100644
> index 000000000..bf885b28c
> --- /dev/null
> +++ b/test/unittest/pid/tst.multi-return.r
> @@ -0,0 +1,7 @@
> +
> +  f_b                                                               1
> +  f_e                                                               1
> +  f_d                                                               2
> +  f_a                                                               3
> +  f_c                                                               4
> +  fN                                                               11
> -- 
> 2.43.5
> 
> 
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