[DTrace-devel] [PATCH 04/14] Track uprobe provider descriptions
Kris Van Hees
kris.van.hees at oracle.com
Tue Jun 4 21:10:24 UTC 2024
On Tue, Jun 04, 2024 at 02:11:03PM -0400, eugene.loh--- via DTrace-devel wrote:
> From: Eugene Loh <eugene.loh at 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 at 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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