[DTrace-devel] [PATCH 05/14] alloca: new faults

[Kris Van Hees]

On Wed, Mar 02, 2022 at 01:44:58PM +0000, Nick Alcock via DTrace-devel wrote:
> We'll use DTRACEFLT_BADSIZE to distinguish in error messages between
> out-of-bounds errors in bcopy and the like, and size-too-large errors.
> (Without this, it's hard to tell if a, say, 0x12 in the fault value
> is a nearly-NULL pointer or a wrong size.)

Makes sense.

> We'll use DTRACEFLT_INTERR to indicate can-never-happen errors where we
> have tested the actual condition already (and emitted a proper error)
> followed by a check to placate the verifier (which will always succeed
> if the actual condition check failed).  The latter failure happening at
> runtime always indicates a bug in DTrace, not in the user's code, so
> indicate as much.

Here I am confused.  If this is a fault that can never happen, why do we
even generate code to report such a non-existant fault?  Based on your
description this would be used in cases where the condition has already
been tested and a proper error has emitted.  Since a probe error results
in an immediate return from the clause function (after reporting the
fault by means of the ERROR probe clauses), the following code will never
execute.

So, I really do not see the need for this new fault that can never happen.

> Signed-off-by: Nick Alcock <nick.alcock at oracle.com>
> ---
>  include/dtrace/faults_defines.h | 2 ++
>  libdtrace/dt_error.c            | 2 ++
>  libdtrace/dt_handle.c           | 1 +
>  3 files changed, 5 insertions(+)
> 
> diff --git a/include/dtrace/faults_defines.h b/include/dtrace/faults_defines.h
> index 20c57ad77499..977db5e57817 100644
> --- a/include/dtrace/faults_defines.h
> +++ b/include/dtrace/faults_defines.h
> @@ -32,6 +32,8 @@
>  #define DTRACEFLT_UPRIV			7	/* Illegal user access */
>  #define DTRACEFLT_TUPOFLOW		8	/* Tuple stack overflow */
>  #define DTRACEFLT_BADSTACK		9	/* Bad stack */
> +#define DTRACEFLT_BADSIZE		10	/* Bad size */
> +#define DTRACEFLT_INTERR		11	/* Internal error */
>  
>  #define DTRACEFLT_LIBRARY		1000	/* Library-level fault */
>  
> diff --git a/libdtrace/dt_error.c b/libdtrace/dt_error.c
> index 50229d271425..5267d23d856b 100644
> --- a/libdtrace/dt_error.c
> +++ b/libdtrace/dt_error.c
> @@ -206,6 +206,8 @@ dtrace_faultstr(dtrace_hdl_t *dtp, int fault)
>  		{ DTRACEFLT_UPRIV,	"invalid user access" },
>  		{ DTRACEFLT_TUPOFLOW,	"tuple stack overflow" },
>  		{ DTRACEFLT_BADSTACK,	"bad stack" },
> +		{ DTRACEFLT_BADSIZE,	"invalid size" },
> +		{ DTRACEFLT_INTERR,	"internal error" },
>  		{ DTRACEFLT_LIBRARY,	"library-level fault" },
>  		{ 0,			NULL }
>  	};
> diff --git a/libdtrace/dt_handle.c b/libdtrace/dt_handle.c
> index 6968b05200b1..ba598cb7861d 100644
> --- a/libdtrace/dt_handle.c
> +++ b/libdtrace/dt_handle.c
> @@ -181,6 +181,7 @@ dt_handle_err(dtrace_hdl_t *dtp, dtrace_probedata_t *data)
>  	case DTRACEFLT_BADADDR:
>  	case DTRACEFLT_BADALIGN:
>  	case DTRACEFLT_BADSTACK:
> +	case DTRACEFLT_BADSIZE:
>  		sprintf(details, " (0x%llx)", (u_longlong_t)err.dteda_addr);
>  		break;
>  
> -- 
> 2.35.0.260.gb82b153193.dirty
> 
> 
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