[cfe-dev] Hack for FreeBSD ABI support

[Eli Friedman]

On Sun, Aug 16, 2009 at 5:45 AM, Anton
Korobeynikov<anton at korobeynikov.info> wrote:
> Hello, Everyone
>
>> There may be some differences between Darwin and FreeBSD (in particular in
>> vector handling, which I didn't test), but with clang using the Darwin ABI I
>> have programs compiled with Clang linking against AppKit compiled with gcc,
>> Foundation compiled with Clang and other frameworks compiled with gcc and
>> working without issue.
> That's rather strange since freebsd folks definitely test the normal
> ELF ABI and never complained about this :) The only difference between
> linux / freebsd found in gcc sources is DEFAULT_PCC_STRUCT_RETURN
> define, which is set to 1 on linux and 0 on bsd. The description is:
>
> @defmac DEFAULT_PCC_STRUCT_RETURN
> Define this macro to be 1 if all structure and union return values must be
> in memory.  Since this results in slower code, this should be defined
> only if needed for compatibility with other compilers or with an ABI at .
> If you define this macro to be 0, then the conventions used for structure
> and union return values are decided by the @code{TARGET_RETURN_IN_MEMORY}
> target hook.
>
> If not defined, this defaults to the value 1.
> @end defmac
>
> So, BSD definitely does not use Darwin ABI (and darwin does not use
> BSD ABI :) ). The hook TARGET_RETURN_IN_MEMORY can be found in
> gcc/config/i386.c under the name ix86_return_memory(). The single use
> of the mentioned flag (pcc_struct_return) is in
> gcc/function.c:aggregate_value_p()
>
> Hopefully this will provide enough information for proper implementation

Note that by "ABI" here only includes the calling convention, and that
makes it sound like FreeBSD is a lot closer to the Darwin calling
convention than the Linux one...

-Eli