Re: Why is __unix__ defined, and not __WINDOWS__ ?

[Agner Fog <agner at agner dot org>]

On 13/05/2019 07.39, Brian Inglis wrote:
> Not quite I believe Cygwin 64 bit programs follow the Unix 64 bit LP64 C
> programming memory model and the System V AMD64 ABI *NOT* the Windows 64 bit
> ILP64 C programming memory model and Microsoft x64 calling convention; see:
> 	http://www.unix.org/version2/whatsnew/lp64_wp.html
> 	https://en.wikipedia.org/wiki/X86_calling_conventions
> - the interface has to be managed by the Cygwin1 dll.

I tried this:

> int test (int x) {
>     return x + 1;
> }
g++ -S -O2 t.cpp

Assembly output from g++ or clang:

> _Z4testi:
> .LFB0:
>         .seh_endprologue
>         leal    1(%rcx), %eax
>         ret
>         .seh_endproc

The Win64 ABI has the paramter in ecx or rcx, the SysV ABI has it in edi.

A dump of the object file shows it is in COFF64 format.

The object file obeys the Win64 ABI and links directly into a Win64 
project. The cygwin dll is not needed if the rest of the executable is 
made with another compiler.

The executable runs under Windows, not under Linux.



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