Re: [PATCH v3 6/8] RISC-V: annotate entry points with type and size

[Jan Beulich <jbeulich@xxxxxxxx>]

On 26.07.2023 17:28, Oleksii wrote:
> On Mon, 2023-07-10 at 10:58 +0200, Jan Beulich wrote:
>> On 10.07.2023 10:56, Jan Beulich wrote:
>>> Use the generic framework in xen/linkage.h. No change in generated
>>> code
>>> except of course the converted symbols change to be hidden ones and
>>> gain
>>> a valid size.
>>>
>>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>>
>> I'm sorry, the Cc list was incomplete here. Adding back the remaining
>> REST
>> maintainers.
>>
>> Jan
>>
>>> ---
>>> Probably count_args_exp() should move to macros.h, but I first
>>> wanted to
>>> see whether anyone can suggest any better approach for checking
>>> whether
>>> a defined macro expands to nothing.
> What about introduction of conditional macros ?
> Something similar to:
> #include <stdio.h>
> 
> #define CONDITIONAL_RETURN(arg1, arg2) CONDITIONAL_RETURN_IMPL(arg1,
> arg2, EMPTY)
> 
> #define EMPTY(...) ""
> 
> #define CONDITIONAL_RETURN_IMPL(arg1, arg2, empty_check) \
>     CONDITIONAL_RETURN_##empty_check(arg1, arg2)
> 
> #define CONDITIONAL_RETURN_EMPTY(arg1, arg2) \
>     CONDITIONAL_RETURN_ARG1(arg1, arg2)
> 
> #define CONDITIONAL_RETURN_ARG1(arg1, arg2) arg1, arg2
> 
> #define CONDITIONAL_RETURN_ARG2(arg1, arg2) arg1

I don't see how this would be used in your scheme. It ...

> int main() {
>     int a = 42;
>     const char* b = "hello";
> 
>     // Second argument is not empty, both arguments are returned
>     printf("Case 1: %d, %s\n", CONDITIONAL_RETURN(a, b));  // Prints:
> Case 1: 42, hello
> 
>     // Second argument is empty, only the first argument is returned
>     printf("Case 2: %d, %s\n", CONDITIONAL_RETURN(a, "")); // Prints:
> Case 2: 42,

... certainly isn't here, or this likely would cause at least a warning
from the compiler (for there being too few arguments to printf()) and
then a runtime UB for interpreting something as a pointer to a string
which likely isn't.

>     return 0;
> }
> 
> and then define DO_CODE_ALIGN using CONDITIONAL_RETURN?

Afaict instead of getting rid of the comma, you'd actually add ""
after it. What am I missing?

Jan