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

[Kris Van Hees]

On Thu, Mar 17, 2022 at 04:37:49PM -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 | 27 ++++++++++++++-------------
>  1 file changed, 14 insertions(+), 13 deletions(-)
> 
> diff --git a/libdtrace/dt_cg.c b/libdtrace/dt_cg.c
> index c40fef41..b78c6e02 100644
> --- a/libdtrace/dt_cg.c
> +++ b/libdtrace/dt_cg.c
> @@ -3316,20 +3316,21 @@ 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
> + * This function is a helper function for subroutines that take one
>   * argument and return the tstring resulting from applying a given BPF
>   * function (passed by name) on it.
>   */
>  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,

I would suggest dt_cg_subr_arg_to_tstring( as function name, to make it more
clear that it relates to a subroutine that takes 1 argument and returns a
tstring.

> +			   const char *fname, int isptr)
>  {
>  	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/

> +	dt_cg_node(arg, dlp, drp);
> +	if (isptr)
> +		dt_cg_check_notnull(dlp, drp, arg->dn_reg);

This should be changed to support alloca pointers:

	if (isptr)
		dt_cg_check_ptr_arg(dlp, drp, arg);

>  	/*
>  	 * The result needs be be a temporary string, so we request one.
> @@ -3346,9 +3347,9 @@ 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);

While dt_cg_tstring_free() is safe to call for any argument, I think you should
actually put a if (isptr) before this, simply because we *know* whether the
argument is a pointer.  The dt_cg_tstring_free() function will still check if
there is a tstring, but if ptr is not a pointer there is no point to even call
it.

>  	emit(dlp,  BPF_MOV_REG(BPF_REG_2, dnp->dn_reg));
>  
> @@ -3359,19 +3360,19 @@ 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  ");

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

>  }
>  
>  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", 1);
>  }
>  
>  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", 1);
>  }
>  
>  /*
> -- 
> 2.18.4
> 
> 
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