-- | Calling conventions. There are basically only two: System V (Linux, OSX, BSD) and Win64\/fastcall

{-# language NoMonomorphismRestriction #-}
{-# language CPP #-}
{-# language DataKinds #-}
module CodeGen.X86.CallConv where

import Foreign
import Data.Monoid

import CodeGen.X86.Asm
import CodeGen.X86.CodeGen

------------------------------------------------------------------------------ 

#if defined (mingw32_HOST_OS) || defined (mingw64_HOST_OS)

-- On Win64 the caller have to reserve 32 byte "shadow space" on the stack (and clean up after)
callFun :: Operand RW S64 -> FunPtr a -> Code
callFun r p = do
  sub rsp 32
  mov r (fromIntegral $ ptrToIntPtr $ castFunPtrToPtr p)
  call r
  add rsp 32

#elif defined (darwin_HOST_OS)

-- OSX requires 16 byte alignment of the stack...
callFun :: Operand RW S64 -> FunPtr a -> Code
callFun r p = do
  push r15              -- we will use r15 (non-volatile) to store old rsp
  mov r15 15            -- 0xf
  not_ r15              -- 0xffff ... fff0
  and_ r15 rsp          -- align rsp into r15
  xchg r15 rsp          -- new rsp = aligned, r15 = old rsp
  mov r (fromIntegral $ ptrToIntPtr $ castFunPtrToPtr p)
  call r
  mov rsp r15           -- restore rsp
  pop r15               -- restore r15

#else

-- helper to call a function
callFun :: Operand RW S64 -> FunPtr a -> Code
callFun r p = do
  mov r $ fromIntegral $ ptrToIntPtr $ castFunPtrToPtr p
  call r

#endif

------------------------------------------------------------------------------ 

-- | Save the non-volatile registers, execute the code, restore the registers 
-- and return after.
--
-- Note: R12..R15 should be preserved on both Windows and Linux (or 
-- System V convention in general). This is the responsability of the 
-- user (this function won't save them, but you can use "saveR12R15" in 
-- addition to this).
--
saveNonVolatile :: Code -> Code
saveNonVolatile code = prologue >> code >> epilogue >> ret

-- | Saves R12, R13, R14 and R15 (on the stack).
saveR12R15 :: Code -> Code
saveR12R15 code = do
  push r12
  push r13
  push r14
  push r15
  code
  pop r15
  pop r14
  pop r13
  pop r12

------------------------------------------------------------------------------ 
-- calling conventions

#if defined (mingw32_HOST_OS) || defined (mingw64_HOST_OS)

---------- Win64 calling convention ----------

arg1 = rcx
arg2 = rdx
arg3 = r8
arg4 = r9
-- rest of the arguments on the stack

result = rax

prologue = do
  push rbp
  push rbx
  push rdi
  push rsi

epilogue = do
  pop rsi
  pop rdi
  pop rbx
  pop rbp

#else

---------- System V calling convention ----------

arg1 = rdi
arg2 = rsi
arg3 = rdx
arg4 = rcx
arg5 = r8
arg6 = r9
-- rest of the arguments on the stack

result = rax

prologue = do
  push rbp
  push rbx

epilogue = do
  pop rbx
  pop rbp

#endif

------------------------------------------------------------------------------