[DTrace-devel] [PATCH 4/5] dynvar: ensure there is always space for at least one dynvar if needed

[Eugene Loh]

Same comments as for aggsize patch (3/5).

On 5/1/23 15:52, Kris Van Hees via DTrace-devel wrote:
> When dynamic variables (or associative arrays) are used, raise the
> dynvarsize option value if needed to ensure there is room for at least
> one dynamic variable (or associative array element).
>
> Signed-off-by: Kris Van Hees <kris.van.hees at oracle.com>
> ---
>   libdtrace/dt_bpf.c                            | 10 ++++--
>   .../assocs/tst.dynvarsize-too-small.d         | 31 +++++++++++++++++++
>   .../assocs/tst.dynvarsize-too-small.r         |  6 ++++
>   3 files changed, 44 insertions(+), 3 deletions(-)
>   create mode 100644 test/unittest/assocs/tst.dynvarsize-too-small.d
>   create mode 100644 test/unittest/assocs/tst.dynvarsize-too-small.r
>
> diff --git a/libdtrace/dt_bpf.c b/libdtrace/dt_bpf.c
> index 0f33f245..e19833bd 100644
> --- a/libdtrace/dt_bpf.c
> +++ b/libdtrace/dt_bpf.c
> @@ -846,9 +846,13 @@ gmap_create_dvars(dtrace_hdl_t *dtp)
>   	if (dtp->dt_maxdvarsize == 0)
>   		return 0;
>   
> -	nelems = dtp->dt_options[DTRACEOPT_DYNVARSIZE] / dtp->dt_maxdvarsize;
> -	if (nelems == 0)
> -		return 0;
> +	nelems = dtp->dt_options[DTRACEOPT_DYNVARSIZE] /
> +		 (dtp->dt_maxtuplesize + dtp->dt_maxdvarsize);
> +	if (nelems == 0) {
> +		dtp->dt_options[DTRACEOPT_DYNVARSIZE] =
> +				dtp->dt_maxtuplesize + dtp->dt_maxdvarsize;
> +		nelems = 1;
> +	}
>   
>   	if (create_gmap(dtp, "dvars", BPF_MAP_TYPE_HASH, sizeof(uint64_t),
>   			dtp->dt_maxdvarsize, nelems) == -1)
> diff --git a/test/unittest/assocs/tst.dynvarsize-too-small.d b/test/unittest/assocs/tst.dynvarsize-too-small.d
> new file mode 100644
> index 00000000..27539194
> --- /dev/null
> +++ b/test/unittest/assocs/tst.dynvarsize-too-small.d
> @@ -0,0 +1,31 @@
> +/*
> + * Oracle Linux DTrace.
> + * Copyright (c) 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.
> + */
> +
> +/*
> + * ASSERTION: If dynvarsize is too small to hold a single dynamic variable, the
> + *	      size is increased automatically.
> + *
> + * SECTION: Aggregations/Aggregations
> + */
> +
> +/*
> + * Storing an int (4 byte integer) in an associative array indexed by an int
> + * requires at least 20 bytes of dynamic variable storage.
> + */
> +#pragma D option quietresize=no
> +#pragma D option dynvarsize=15
> +
> +BEGIN
> +{
> +	a[1] = 1;
> +	exit(0);
> +}
> +
> +ERROR
> +{
> +	exit(1);
> +}
> diff --git a/test/unittest/assocs/tst.dynvarsize-too-small.r b/test/unittest/assocs/tst.dynvarsize-too-small.r
> new file mode 100644
> index 00000000..b236110f
> --- /dev/null
> +++ b/test/unittest/assocs/tst.dynvarsize-too-small.r
> @@ -0,0 +1,6 @@
> +                   FUNCTION:NAME
> +                          :BEGIN
> +
> +-- @@stderr --
> +dtrace: script 'test/unittest/assocs/tst.dynvarsize-too-small.d' matched 2 probes
> +dtrace: dynamic variable size raised to 20