[DTrace-devel] [PATCH v2 17/17] strings: handle null strings in the ternary conditional op

[Eugene Loh]

I'll look more tomorrow.  Right now I'll just say I'm not getting the 
commit message and in any case I would think a test should accompany the 
patch.

On 3/14/22 5:30 PM, Nick Alcock wrote:
> This will fault if the result is a null string now that dt_cg_memcpy is
> error-checked.  (It is not enough to make strings work: dt_cg_store_var
> is doing the same thing, preventing you even *assigning* NULL to a
> string. Not sure how to fix that.)
>
> Signed-off-by: Nick Alcock <nick.alcock at oracle.com>
> ---
>   libdtrace/dt_cg.c | 6 ++++++
>   1 file changed, 6 insertions(+)
>
> diff --git a/libdtrace/dt_cg.c b/libdtrace/dt_cg.c
> index c940ce7b8bc6..0084798bcde6 100644
> --- a/libdtrace/dt_cg.c
> +++ b/libdtrace/dt_cg.c
> @@ -3478,6 +3478,10 @@ dt_cg_ternary_op(dt_node_t *dnp, dt_irlist_t *dlp, dt_regset_t *drp)
>   	 * dn_right).
>   	 */
>   	if (dt_node_is_string(dnp)) {
> +		uint_t lbl_null = dt_irlist_label(dlp);
> +
> +		emit(dlp,  BPF_BRANCH_IMM(BPF_JEQ, dnp->dn_reg, 0, lbl_null));
> +
>   		/*
>   		 * At this point, dnp->dn_reg holds a pointer to the string we
>   		 * need to copy.  But we want to copy it into a tstring which
> @@ -3494,6 +3498,8 @@ dt_cg_ternary_op(dt_node_t *dnp, dt_irlist_t *dlp, dt_regset_t *drp)
>   		dt_cg_memcpy(dlp, drp, dnp->dn_reg, BPF_REG_0,
>   			     yypcb->pcb_hdl->dt_options[DTRACEOPT_STRSIZE]);
>   
> +		emitl(dlp,  lbl_null,
> +			    BPF_NOP());
>   		dt_cg_tstring_free(yypcb, dnp->dn_left);
>   		dt_cg_tstring_free(yypcb, dnp->dn_right);
>   	}