[DTrace-devel] [PATCH] Add support for array/struct/union to trace()

[Kris Van Hees]

On Thu, Jan 27, 2022 at 11:01:56PM -0500, Kris Van Hees via DTrace-devel wrote:
> On Thu, Jan 27, 2022 at 05:11:18PM -0500, Eugene Loh via DTrace-devel wrote:
> > On 1/26/22 11:26 AM, Kris Van Hees via DTrace-devel wrote:
> > > +	if (kind == DTRACEACT_DIFEXPR && (arg & DT_NF_REF)) {
> > > +		off = dt_rec_add(dtp, dt_cg_fill_gap, kind,
> > > +				 size, size, pfp, arg);
> > 
> > For dt_rec_add(), why is the alignment "size" rather than 1?
> 
> Good catch.  Cut'n'paste error.  I am not certain that 1 will be the best
> alignment here because we may want a struct, union, or array at its proper
> alignment based on the conte type(s), but for now I will go with it.  We
> can revisit this if/when we might consider providing annotated output.

Looking into this a bit more, the trouble with setting alignment to be 1 is
that it makes it impossible to distinguish between string data and non-string
data.  The trace processing in the consumer uses the alignment, so I need to
either have the alignment be >= 2 and <= 8 (since more than 8 is pointless)
or somehow ensure that the trace processing can know what type of data it is
looking at.  I don't want to add more fields to the recdata so I'll see if I
can use dtrd_arg for this, or I'll ust an alignment of 2, 4, or 8 depending on
the data size.

Stay tuned...