[DTrace-devel] [PATCH 3/3] Implement argument retrieval for SDT probes

[Eugene Loh]

Reviewed-by: Eugene Loh <eugene.loh at oracle.com>
Thanks for your earlier note on testing but this patch really seems to 
need something, as hard as that something is to come up with.

And...

On 7/2/21 2:19 PM, Kris Van Hees wrote:
> Signed-off-by: Kris Van Hees <kris.van.hees at oracle.com>
> ---
>   libdtrace/dt_prov_sdt.c | 16 +++++++++-------
>   1 file changed, 9 insertions(+), 7 deletions(-)
>
> diff --git a/libdtrace/dt_prov_sdt.c b/libdtrace/dt_prov_sdt.c
> index 712f533f..b4d6189b 100644
> --- a/libdtrace/dt_prov_sdt.c
> +++ b/libdtrace/dt_prov_sdt.c
> @@ -126,8 +126,6 @@ static int populate(dtrace_hdl_t *dtp)
>    * The trampoline will populate a dt_dctx_t struct and then call the function
>    * that implements the compiled D clause.  It returns the value that it gets
>    * back from that function.
> - *
> - * FIXME: Currently, access to arguments of the tracepoint is not supported.
>    */
>   static void trampoline(dt_pcb_t *pcb)
>   {
> @@ -145,12 +143,16 @@ static void trampoline(dt_pcb_t *pcb)
>   	dt_cg_tramp_clear_regs(pcb);
>   
>   	/*
> -	 *	for (i = 0; i < ARRAY_SIZE(((dt_mstate_t *)0)->argv); i++)
> -	 *		dctx->mst->argv[i] = 0
> -	 *				// stdw [%r7 + DMST_ARG(i)], 0
> +	 *      for (i = 0; i < argc; i++)
> +	 *              dctx->mst->argv[i] = ((uint64_t *)ctx)[i + 1];
> +	 *				//     (first value is private)
> +	 *                              // lddw %r0, [%r8 + (i + 1) * 8]
> +	 *                              // stdw [%r7 + DMST_ARG(i)], 0

No big deal, but I thought you preferred tabs over spaces for alignment.

Also, update comment to stdw r0 rather than 0.

>   	 */
> -	for (i = 0; i < pcb->pcb_pinfo.dtp_argc; i++)
> -		emit(dlp, BPF_STORE_IMM(BPF_DW, BPF_REG_7, DMST_ARG(i), 0));
> +	for (i = 0; i < pcb->pcb_pinfo.dtp_argc; i++) {
> +		emit(dlp, BPF_LOAD(BPF_DW, BPF_REG_0, BPF_REG_8, (i + 1) * 8));
> +		emit(dlp, BPF_STORE(BPF_DW, BPF_REG_7, DMST_ARG(i), BPF_REG_0));
> +	}
>   
>   	dt_cg_tramp_epilogue(pcb);
>   }