[DTrace-devel] [PATCH v2] Add support for built-in variable execname

[Eugene Loh]

You can add my
           Reviewed-by: Eugene Loh <eugene.loh at oracle.com>
to Nick's if you like.  I'm curious about two things:

On 1/27/22 2:11 PM, Kris Van Hees via DTrace-devel wrote:
> diff --git a/bpf/get_bvar.c b/bpf/get_bvar.c
> +	case DIF_VAR_EXECNAME: {
> +		uint64_t	ptr;
> +		uint32_t	key;
> +		uint32_t	*comm_off;
> +
> +		/*
> +		 * In the "state" map, look up the "struct task_struct" offset
> +		 * of "comm".
> +		 */
> +		key = DT_STATE_TASK_COMM_OFF;
> +		comm_off = bpf_map_lookup_elem(&state, &key);
> +		if (comm_off == NULL)
> +			return 0;
> +
> +		/* &(current->comm) */
> +		ptr = bpf_get_current_task();
> +		if (ptr == 0)
> +			return error(dctx, DTRACEFLT_BADADDR, ptr);
> +
> +		return (uint64_t)ptr + *comm_off;
> +	}

How are the error behaviors determined?  That is, why "return 0" in one 
case and "return error(BADADDR)" in the other?

> diff --git a/test/unittest/variables/bvar/tst.execname.d b/test/unittest/variables/bvar/tst.execname.d
> @@ -1,10 +1,9 @@
>   /*
>    * Oracle Linux DTrace.
> - * Copyright (c) 2020, 2021, Oracle and/or its affiliates. All rights reserved.
> + * Copyright (c) 2020, 2022, 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.
>    */
> -/* @@xfail: dtv2 */
>   
>   /*
>    * ASSERTION: The 'execname' variable can be accessed and is not -1.

The comment describing the test should be updated to reflect the change 
in the test's behavior.

> @@ -16,7 +15,7 @@
>   
>   BEGIN {
>   	trace(execname);
> -	exit(execname != -1 ? 0 : 1);
> +	exit(0);
>   }
>   
>   ERROR {