[DTrace-devel] [PATCH v2 1/3] Rename "path" helper to "tstring1" helper

[Kris Van Hees]

On Fri, Mar 18, 2022 at 03:36:42PM -0400, eugene.loh--- via DTrace-devel wrote:
> From: Eugene Loh <eugene.loh at oracle.com>
> 
> When the code generator sets up a call to a precompiled BPF function,
> it emits a lot of boilerplate code.  The implementations of DTrace
> subroutines typically make such calls.  So there is potential for
> much code reuse.
> 
> The "path" helper is one such attempt.  Since its usefulness is
> broader than just for a "path name" argument, rename this helper to
> suggest its broader usage more clearly.
> 
> Signed-off-by: Eugene Loh <eugene.loh at oracle.com>
> ---
>  libdtrace/dt_cg.c | 39 +++++++++++++++++++++------------------
>  1 file changed, 21 insertions(+), 18 deletions(-)
> 
> diff --git a/libdtrace/dt_cg.c b/libdtrace/dt_cg.c
> index c40fef41..b8325e44 100644
> --- a/libdtrace/dt_cg.c
> +++ b/libdtrace/dt_cg.c
> @@ -3316,24 +3316,27 @@ dt_cg_array_op(dt_node_t *dnp, dt_irlist_t *dlp, dt_regset_t *drp)
>  }
>  
>  /*
> - * This function is a helper function for subroutines that take a path
> - * argument and return the tstring resulting from applying a given BPF
> - * function (passed by name) on it.
> + * This helper emits code to call a precompiled BPF function (named
> + * by fname) that is of return type void and takes two arguments:
> + *   - one input value
> + *   - a pointer to an output tstring, allocated here
>   */
>  static void
> -dt_cg_subr_path_helper(dt_node_t *dnp, dt_irlist_t *dlp, dt_regset_t *drp,
> -		       const char *fname)
> +dt_cg_subr_tstring1_helper(dt_node_t *dnp, dt_irlist_t *dlp, dt_regset_t *drp,
> +			   const char *fname)

s/dt_cg_subr_tstring1_helper/dt_cg_subr_arg_to_tstring/

>  {
>  	dt_ident_t	*idp;
> -	dt_node_t	*str = dnp->dn_args;
> +	dt_node_t	*arg = dnp->dn_args;
>  
> -	TRACE_REGSET("    subr-path_helper:Begin");
> -	dt_cg_node(str, dlp, drp);
> -	dt_cg_check_notnull(dlp, drp, str->dn_reg);
> +	TRACE_REGSET("    subr-tstring1_helper:Begin");

s/subr-tstring1_helper/subr-arg-to-tstring/

>  
> -	/*
> -	 * The result needs be be a temporary string, so we request one.
> -	 */
> +	/* handle the one "input value" */
> +	/* (its type matters only as to whether we check it is null */
> +	dt_cg_node(arg, dlp, drp);
> +	if (dt_node_is_pointer(arg) || dt_node_is_string(arg))
> +		dt_cg_check_notnull(dlp, drp, arg->dn_reg);

This should be changed to support alloca pointers:

	if (dt_node_is_pointer(arg) || dt_node_is_string(arg))
		dt_cg_check_ptr_arg(dlp, drp, arg);

> +
> +	/* allocate the temporary string */
>  	dnp->dn_reg = dt_regset_alloc(drp);
>  	if (dnp->dn_reg == -1)
>  		longjmp(yypcb->pcb_jmpbuf, EDT_NOREG);
> @@ -3346,9 +3349,9 @@ dt_cg_subr_path_helper(dt_node_t *dnp, dt_irlist_t *dlp, dt_regset_t *drp,
>  	if (dt_regset_xalloc_args(drp) == -1)
>  		longjmp(yypcb->pcb_jmpbuf, EDT_NOREG);
>  
> -	emit(dlp, BPF_MOV_REG(BPF_REG_1, str->dn_reg));
> -	dt_regset_free(drp, str->dn_reg);
> -	dt_cg_tstring_free(yypcb, str);
> +	emit(dlp, BPF_MOV_REG(BPF_REG_1, arg->dn_reg));
> +	dt_regset_free(drp, arg->dn_reg);
> +	dt_cg_tstring_free(yypcb, arg);

How about:

	if (dt_node_is_string(arg))
		dt_cg_tstring_free(yypcb, arg);

>  
>  	emit(dlp,  BPF_MOV_REG(BPF_REG_2, dnp->dn_reg));
>  
> @@ -3359,19 +3362,19 @@ dt_cg_subr_path_helper(dt_node_t *dnp, dt_irlist_t *dlp, dt_regset_t *drp,
>  	dt_regset_free_args(drp);
>  	dt_regset_free(drp, BPF_REG_0);
>  
> -	TRACE_REGSET("    subr-path_helper:End  ");
> +	TRACE_REGSET("    subr-tstring1_helper:End  ");
>  }
>  
>  static void
>  dt_cg_subr_basename(dt_node_t *dnp, dt_irlist_t *dlp, dt_regset_t *drp)
>  {
> -	dt_cg_subr_path_helper(dnp, dlp, drp, "dt_basename");
> +	dt_cg_subr_tstring1_helper(dnp, dlp, drp, "dt_basename");
>  }
>  
>  static void
>  dt_cg_subr_dirname(dt_node_t *dnp, dt_irlist_t *dlp, dt_regset_t *drp)
>  {
> -	dt_cg_subr_path_helper(dnp, dlp, drp, "dt_dirname");
> +	dt_cg_subr_tstring1_helper(dnp, dlp, drp, "dt_dirname");
>  }
>  
>  /*
> -- 
> 2.18.4
> 
> 
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