Incorrect __fastcall ABI

[chuggafan]

If I'm reading this right, we treat __fastcall as having three register parameters and the rest passed on the stack, those register parameters for us are ECX, EDX, and EAX.

static char fastcallRegs[3] = {R_ECX, R_EDX, R_EAX};

(Gotten from line 340 of configx86.cpp)

Whereas the Microsoft docs for fastcall state:

Element	Implementation
Argument-passing order	The first two DWORD or smaller arguments that are found in the argument list from left to right are passed in ECX and EDX registers; all other arguments are passed on the stack from right to left.

https://learn.microsoft.com/en-us/cpp/cpp/fastcall?view=msvc-170
Not sure if just chopping off that EAX portion at the end will work since we have builtins that rely on fastcall ordering.

[LADSoft]

honestly, I didn't think to look to figure out how it should work..... didn't realize there would be a standard for it lol... yeah it would be a bit of a problem to chenge it because of the way we are using it for intrinsics, but there might only be a couple of intrinsics that are effected.

I've been thinking about reviving the 'ecx as thisptr' project because if I could get that to work reliably we might be able to use microsoft C++ dlls more directly.... at least whenever we switch the name mangling over sigh.... but i think you pointed out we could just borrow the clang code for name mangling more or less and take care of that issue.... ( I think I also saw name mangling code in the libcxx sources but don't remember for sure).

[chuggafan]

Yhea, Microsoft publishes a lot of stuff out there now ;)
There's also the x64 spec for windows on calling conventions.
https://learn.microsoft.com/en-us/cpp/build/x64-calling-convention?view=msvc-170

[LADSoft]

yeah i was aware of the x654 spec, i was going to comply with it when we get there.....