Re: [PATCH v3 1/3] Use enum for return method for dummy calls

[Pedro Alves <palves at redhat dot com>]

On 10/11/2018 03:49 PM, Alan Hayward wrote:
> In call_function_by_hand_dummy, struct_return and hidden_first_param_p
> are used to represent a single concept. Replace with an enum.
> 
> gdb/ChangeLog:
> 
> 2018-10-11  Alan Hayward  <alan.hayward@arm.com>
> 
> 	* gdbarch.sh (enum function_call_return_method): Add enum.
> 	* gdbarch.h: Regenerate.
> 	* infcall.c (call_function_by_hand_dummy): Replace vars with enum.
> ---
>  gdb/gdbarch.h  | 17 +++++++++++++++++
>  gdb/gdbarch.sh | 17 +++++++++++++++++
>  gdb/infcall.c  | 29 +++++++++++------------------
>  3 files changed, 45 insertions(+), 18 deletions(-)
> 
> diff --git a/gdb/gdbarch.h b/gdb/gdbarch.h
> index fc2f1a84a1..5f9cf481fb 100644
> --- a/gdb/gdbarch.h
> +++ b/gdb/gdbarch.h
> @@ -102,6 +102,23 @@ typedef void (iterate_over_regset_sections_cb)
>    (const char *sect_name, int supply_size, int collect_size,
>     const struct regset *regset, const char *human_name, void *cb_data);
>  
> +/* For a function call, are we returning a value using a normal value return
> +   or a structure return - passing a hidden argument pointing to storage.

Pedantically, this is not a property of the call action that
we're performing, but a property of the function's call ABI.
I'd suggest tweaking the sentence like this:

/* For a function call, does the function return a value using a
   normal value return or a structure return - passing a hidden
   argument pointing to storage.

> +   There are two cases: language-mandated structure return and target ABI
> +   structure return.  

That "There are two cases" is a bit confusing, because it makes you think
about normal vs not-normal.  So I'd suggest starting with "For the latter", like:

   For the latter, there are two cases: language-mandated structure
   return and target ABI [....]

The language version is handled by passing the return
> +   location as the first parameter to the function, even preceding "this".
> +   This is different from the target ABI version, which is target-specific; for
> +   instance, on ia64 the first argument is passed in out0 but the hidden
> +   structure return pointer would normally be passed in r8.  */
> +
> +enum function_call_return_method
> +{
> +  return_method_normal = 0,	/* Standard value return.  */
> +  return_method_struct,		/* target ABI structure return.  */

Uppercase "target" -> "Target".

> +  return_method_hidden_param	/* Return hidden in first param.  */

These last two are confusing if you consider the comment in the intro
that says:

 "or a structure return - passing a hidden argument pointing to storage."

I.e., as is, makes you wonder whether "return_method_struct" is
or is not a hidden param too?

> +};
> +

Keeping the enum/enumerators names, how about this:

/* For a function call, does the function return a value using a
   normal value return or a structure return - passing a hidden
   argument pointing to storage.  For the latter, there are two
   cases: language-mandated structure return and target ABI
   structure return.  */

enum function_call_return_method
{
  /* Standard value return.  */
  return_method_normal = 0,

  /* Language ABI structure return.  This is handled
     by passing the return location as the first parameter to
     the function, even preceding "this".
  return_method_hidden_param,

  /* Target ABI struct return.  This is target-specific; for instance,
     on ia64 the first argument is passed in out0 but the hidden
     structure return pointer would normally be passed in r8.  */
  return_method_struct,
};

Thanks,
Pedro Alves