Importing C function with variable argument list

[Maxim Reznik <reznikmm@gmail.com>]

Hi, All

It seems it's impossible to call C function variable argument lists
from Ada.
Even when one knows in advace all arguments at compile time.

Functions with Variable Argument Lists have their own ABI. For
instance, in x86_64:

> When a function taking variable-arguments is called, %rax must be set to the
> total number of floating point parameters passed to the function in vector registers.

But it's impossible to specify this fact in pragma Import (C, ...

Small example:

C declaration:
void syslog (int __pri, __const char *__fmt, ...);

Supposed Import declaration:

procedure C_Syslog (Priority : int; Format : chars_ptr; Msg :
chars_ptr);
pragma Import (C, C_Syslog, "syslog");

Call to C_Syslog fails, because %rax has not zero value.

What do you think?