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

Pedro Alves
2018-10-19T11:28:34Z

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