[DTrace-devel] [PATCH 04/05] dynvar: report error if dynvarsize is too small

[Kris Van Hees]

On Mon, May 08, 2023 at 01:32:06PM -0400, Eugene Loh via DTrace-devel wrote:
> Reviewed-by: Eugene Loh <eugene.loh at oracle.com>
> though...
> 
> On 5/5/23 11:33, Kris Van Hees via DTrace-devel wrote:
> > When dynamic variables (or associative arrays) are used, ensure that the
> > dynvarsize value is sufficient to hold at least one dynamic variable
> > (or associative array element).
> 
> Comment is not true and in fact conflicts with the subject line.

Same as other patch.  That'w what I get for fixing things up while still
significantly under the weather.  Thanks for catching.

> > Signed-off-by: Kris Van Hees<kris.van.hees at oracle.com>
> > ---
> >   libdtrace/dt_bpf.c                            |  5 ++--
> >   .../assocs/err.dynvarsize-too-small.d         | 30 +++++++++++++++++++
> >   .../assocs/err.dynvarsize-too-small.r         |  3 ++
> >   3 files changed, 36 insertions(+), 2 deletions(-)
> >   create mode 100644 test/unittest/assocs/err.dynvarsize-too-small.d
> >   create mode 100644 test/unittest/assocs/err.dynvarsize-too-small.r
> > 
> > diff --git a/libdtrace/dt_bpf.c b/libdtrace/dt_bpf.c
> > index b553b33f..a00b353d 100644
> > --- a/libdtrace/dt_bpf.c
> > +++ b/libdtrace/dt_bpf.c
> > @@ -843,9 +843,10 @@ gmap_create_dvars(dtrace_hdl_t *dtp)
> >   	if (dtp->dt_maxdvarsize == 0)
> >   		return 0;
> > -	nelems = dtp->dt_options[DTRACEOPT_DYNVARSIZE] / dtp->dt_maxdvarsize;
> > +	nelems = dtp->dt_options[DTRACEOPT_DYNVARSIZE] /
> > +		 (dtp->dt_maxtuplesize + dtp->dt_maxdvarsize);
> 
> Okay but also +2*sizeof(uint64_t)?
> 
> I'm pretty sure these models are rather approximate.  The user might think
> they're specifying how much room is being taken up but that's not what's
> going on.  We're simply using the dynvarsize value to size nelems, and the
> actual footprint is... complicated.  So the real point is perhaps that
> dynvarsize is an out-dated notion, and ndynelems (or something) should take
> its place.  For now, I suppose it's enough to support the historical option
> in the least torturous manner we can think of.
> 
> >   	if (nelems == 0)
> > -		return 0;
> > +		return dt_set_errno(dtp, EDT_BUFTOOSMALL);
> >   	if (create_gmap(dtp, "dvars", BPF_MAP_TYPE_HASH, sizeof(uint64_t),
> >   			dtp->dt_maxdvarsize, nelems) == -1)
> > diff --git a/test/unittest/assocs/err.dynvarsize-too-small.d b/test/unittest/assocs/err.dynvarsize-too-small.d
> > new file mode 100644
> > index 00000000..02fa4f8a
> > --- /dev/null
> > +++ b/test/unittest/assocs/err.dynvarsize-too-small.d
> > @@ -0,0 +1,30 @@
> > +/*
> > + * 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,
> > + *	      report an error.
> > + *
> > + * 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 dynvarsize=15
> 
> The comment is hard to understand:  how is 4+4>=20?  And why is
> dynvarsize=15 instead of, say, 19?  And then how about a tst.dynvarsize.d
> with dynvarsize=20 (or whatever it's supposed to be)?
> 
> > +
> > +BEGIN
> > +{
> > +	a[1] = 1;
> > +	exit(0);
> > +}
> > +
> > +ERROR
> > +{
> > +	exit(1);
> > +}
> > diff --git a/test/unittest/assocs/err.dynvarsize-too-small.r b/test/unittest/assocs/err.dynvarsize-too-small.r
> > new file mode 100644
> > index 00000000..4b56154d
> > --- /dev/null
> > +++ b/test/unittest/assocs/err.dynvarsize-too-small.r
> > @@ -0,0 +1,3 @@
> > +-- @@stderr --
> > +dtrace: script 'test/unittest/assocs/err.dynvarsize-too-small.d' matched 2 probes
> > +dtrace: could not enable tracing: Enabling exceeds size of buffer
> > -- 2.40.1
> 
> _______________________________________________
> DTrace-devel mailing list
> DTrace-devel at oss.oracle.com
> https://oss.oracle.com/mailman/listinfo/dtrace-devel