[DTrace-devel] [PATCH v2 01/04] probe: propagate dt_probe_args_info() failures to dt_probe_info()

[Nick Alcock]

On 30 Nov 2023, Kris Van Hees via DTrace-devel stated:

> Failures in dt_probe_args_info() were ignored by dt_probe_info() and
> that could lead to strange behaviour.  E.g. if lockmem issues cause
> the logic in the raw tracepoint argument count determination to fail,
> the probe was reported as not having any arguments.  This patch will
> make it possible to add code to accurately report such failures
> rather than silently ignoring them.

Good idea, but...

> diff --git a/cmd/dtrace.c b/cmd/dtrace.c
> index e7ca9e4c..9c820686 100644
> --- a/cmd/dtrace.c
> +++ b/cmd/dtrace.c
> @@ -323,6 +323,8 @@ info_stmt(dtrace_hdl_t *dtp, dtrace_prog_t *pgp,
>  
>  	if (dtrace_probe_info(dtp, pdp, &p) == 0)
>  		print_probe_info(&p);
> +	else
> +		return -1;

So dtrace_probe_info()'s error returns do not emit any errors anywhere:
they just set the dtrace_errno. On error, this doesn't emit any errors either...

>  	*last = edp;
>  	return 0;
> @@ -417,8 +419,12 @@ list_probe(dtrace_hdl_t *dtp, const dtrace_probedesc_t *pdp, void *arg)
>  	oprintf("%5d %10s %17s %33s %s\n",
>  		pdp->id, pdp->prv, pdp->mod, pdp->fun, pdp->prb);
>  
> -	if (g_verbose && dtrace_probe_info(dtp, pdp, &p) == 0)
> -		print_probe_info(&p);
> +	if (g_verbose) {
> +		if (dtrace_probe_info(dtp, pdp, &p) == 0)
> +			print_probe_info(&p);
> +		else
> +			return -1;
> +	}

... so nor does this; and then this call, which you didn't touch:

	case DMODE_LIST:
[...]		if (g_cmdc == 0)
			dtrace_probe_iter(g_dtp, NULL, list_probe, NULL);

		dtrace_close(g_dtp);
		return g_status;

... exits early without printing the dtrace_errmsg. You might want to
check all the dtrace_probe_iter()s that call list_probe() for error
returns, perhaps?

> @@ -1426,8 +1432,10 @@ main(int argc, char *argv[])
>  		for (i = 0; i < g_cmdc; i++)
>  			list_prog(&g_cmdv[i]);
>  
> -		if (g_cmdc == 0)
> -			dtrace_probe_iter(g_dtp, NULL, list_probe, NULL);
> +		if (g_cmdc == 0) {
> +			if (dtrace_probe_iter(g_dtp, NULL, list_probe, NULL) < 0)
> +				dfatal(NULL); /* dtrace_errmsg() only */
> +		}

Like you do here :)

The changes to dt_probe.c look good.

-- 
NULL && (void)