While msabi and sysv do agree what to do with floating point args for 4 floating point args (pass in xmm0-4), they dont agree what to do with mixing
msabi will choose the register corresponding with argument position. so if you have (int foo, float bar), bar will use xmm1
sysv instead will choose the first register available in the group. so with the previous example, you instead have bar using xmm0
the simple solution is to simply prohibit mixed args for now. maybe someday we could support mixing, but that's probably overkill (best use a struct at that point)
make a small dll for handling the msabi<->sysv adapter, using only assembly (taken from generated optimized rustc output) and handcrafted unwind information (c# exceptions in a callback seem to work fine in testing)
additionally, allow floating point arguments. this really only needs to occur on the c# side. msabi and sysv agree on the first 4 floating point args and for returns, so no work actually has to be done adapting these
with assembly being used, we can guarantee rax will not be stomped by compiler whims (and avoid potential floating point args from being trashed)
CasualPokePlayer