Re: [DTrace-devel] [PATCH 04/14] Track uprobe provider descriptions

[Kris Van Hees <kris.van.hees@oracle.com>]

On Tue, Jun 04, 2024 at 02:11:03PM -0400, eugene.loh--- via DTrace-devel wrote:
> From: Eugene Loh <eugene.loh@oracle.com>
> 
> A uprobe will have to decide which of its clauses to run for a
> given pid.  For now, keep the provider description for each clause.
> There are many shortcomings to the way this is done in this patch,
> but it is quick and dirty and helps us bootstrap real support.
> Clean this up later, probably turning it into a growable array.

This is the wrong way to look at it, I think.  The underlying concept is that
DTrace supports specifying probes that do not match anything yet (-Z).  Those
are called retained enablings and they can exist for more than just uprobes.
So this needs to be more generic.

We also shouldn't do this non-discriminately for all clauses all the time.
Obviously, when -Z is not used, there is no point in doing this because there
cannot be a match-after-start.  Even when -Z is specified, you might be able
to determine whether the probe specification for a probe matches perfectly
or whether it needs to be retained for match-after-start.

So, let's put some thought into designing this in the more generic case, so
that we can avoid going down a rabbit hole that gets tough to recover from.

(And whatever we store the retained enablings in probably should be added to
 dtrace_hdl_t after dt_enablings.)

> Signed-off-by: Eugene Loh <eugene.loh@oracle.com>
> ---
>  libdtrace/dt_cc.c   | 1 +
>  libdtrace/dt_impl.h | 1 +
>  2 files changed, 2 insertions(+)
> 
> diff --git a/libdtrace/dt_cc.c b/libdtrace/dt_cc.c
> index d1ee3843..6bff7e0f 100644
> --- a/libdtrace/dt_cc.c
> +++ b/libdtrace/dt_cc.c
> @@ -215,6 +215,7 @@ dt_compile_one_clause(dtrace_hdl_t *dtp, dt_node_t *cnp, dt_node_t *pnp)
>  	 */
>  	dt_cg(yypcb, cnp);
>  	sdp->dtsd_clause = dt_clause_create(dtp, dt_as(yypcb));
> +	dtp->dt_uprovdescs[dtp->dt_clause_nextid - 1] = strdup(pnp->dn_desc->prv);
>  
>  	assert(yypcb->pcb_stmt == sdp);
>  	if (dtrace_stmt_add(yypcb->pcb_hdl, yypcb->pcb_prog, sdp) != 0)
> diff --git a/libdtrace/dt_impl.h b/libdtrace/dt_impl.h
> index 01313ff3..1bf79d80 100644
> --- a/libdtrace/dt_impl.h
> +++ b/libdtrace/dt_impl.h
> @@ -310,6 +310,7 @@ struct dtrace_hdl {
>  	dt_pcb_t *dt_pcb;	/* pointer to current parsing control block */
>  	ulong_t dt_gen;		/* compiler generation number */
>  	uint_t dt_clause_nextid; /* next ID to use for programs */
> +	char *dt_uprovdescs[256]; /* uprobe provider descriptor per clause... FIXME turn this into a growable array */
>  	dt_list_t dt_programs;	/* linked list of dtrace_prog_t's */
>  	dt_list_t dt_xlators;	/* linked list of dt_xlator_t's */
>  	dt_list_t dt_enablings;	/* list of (to be) enabled probes */
> -- 
> 2.18.4
> 
> 
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