[DTrace-devel] [PATCH 2/7 v2 REVIEWED] Make dt_cg_ldsize() available to provider implementations

[Eugene Loh]

On 5/27/22 22:36, Kris Van Hees via DTrace-devel wrote:

> Code generation for probe program trampolines will need dt_cg_ldsize()
> (formetly known as dt_cg_load()) to generate the correct load
> instructions when populating the probe argument data.

formetly
->
formerly

Incidentally, why is the new name ld-specific?  I suppose that reflects 
current usage, but it could be used for st as well; further, it is 
looking stuff up in an array called ldstw[] (which I assume means 
load-store width).

I also am not familiar with the code below.  What is the "sign bit" 
comment referring to?

> diff --git a/libdtrace/dt_cg.c b/libdtrace/dt_cg.c
> @@ -5032,16 +5028,17 @@ dt_cg_node(dt_node_t *dnp, dt_irlist_t *dlp, dt_regset_t *drp)
>   			ssize_t	size;
>   
>   			/*
> -			 * Save and restore DT_NF_USERLAND across dt_cg_load():
> -			 * we need the sign bit from dnp and the user bit from
> -			 * dnp->dn_child in order to get the proper opcode.
> +			 * Save and restore DT_NF_USERLAND across
> +			 * dt_cg_ldsize(): we need the sign bit from dnp and
> +			 * the user bit from dnp->dn_child in order to get the
> +			 * proper opcode.
>   			 */
>   			ubit = dnp->dn_flags & DT_NF_USERLAND;
>   			dnp->dn_flags |=
>   			    (dnp->dn_child->dn_flags & DT_NF_USERLAND);
>   
>   			dt_cg_check_notnull(dlp, drp, dnp->dn_reg);
> -			op = dt_cg_load(dnp, ctfp, dnp->dn_type, &size);
> +			op = dt_cg_ldsize(dnp, ctfp, dnp->dn_type, &size);
>   
>   			/*
>   			 * If the child is an alloca pointer, bounds-check it
> @@ -5205,16 +5202,17 @@ dt_cg_node(dt_node_t *dnp, dt_irlist_t *dlp, dt_regset_t *drp)
>   			uint_t ubit;
>   
>   			/*
> -			 * Save and restore DT_NF_USERLAND across dt_cg_load():
> -			 * we need the sign bit from dnp and the user bit from
> -			 * dnp->dn_left in order to get the proper opcode.
> +			 * Save and restore DT_NF_USERLAND across
> +			 * dt_cg_ldsize(): we need the sign bit from dnp and
> +			 * the user bit from dnp->dn_left in order to get the
> +			 * proper opcode.
>   			 */
>   			ubit = dnp->dn_flags & DT_NF_USERLAND;
>   			dnp->dn_flags |=
>   			    (dnp->dn_left->dn_flags & DT_NF_USERLAND);
>   
>   			/* FIXME: Does not handle signed and userland */
> -			emit(dlp, BPF_LOAD(dt_cg_load(dnp, ctfp, m.ctm_type, NULL),
> +			emit(dlp, BPF_LOAD(dt_cg_ldsize(dnp, ctfp, m.ctm_type, NULL),
>   					   dnp->dn_left->dn_reg, dnp->dn_left->dn_reg, 0));
>   
>   			dnp->dn_flags &= ~DT_NF_USERLAND;
>   }