使用带有C函数的`foreign import prim`使用STG调用约定

Question

我有一个简单的C例程,它接受四个单词并返回四个单词,gcc可以优化并发出一些GHC不支持的初始化.我正在尝试以各种方式调用此过程,并且无法尝试使用此处描述的技术foreign import prim.

以下是为每个输入单词添加1,但是段错误.

Main.hs:

{-# LANGUAGE GHCForeignImportPrim #-}
{-# LANGUAGE ForeignFunctionInterface #-}
{-# LANGUAGE MagicHash #-}
{-# LANGUAGE UnboxedTuples  #-}
{-# LANGUAGE UnliftedFFITypes #-}
import Foreign.C
import GHC.Prim
import GHC.Int
import GHC.Word

foreign import prim "sipRound"
  sipRound_c# :: Word# -> Word# -> Word# -> Word# -> (# Word#, Word#, Word#, Word# #)

sipRound_c ::  Word64 -> Word64 -> Word64 -> Word64 -> (Word64, Word64, Word64, Word64)
sipRound_c (W64# v0) (W64# v1) (W64# v2) (W64# v3) = case sipRound_c# v0 v1 v2 v3 of
  (# v0', v1', v2', v3' #) -> (W64# v0', W64# v1', W64# v2', W64# v3')

main = do
  print $ sipRound_c 1 2 3 4

sip.c:

#include <stdlib.h>
#include <stdint.h>
#include <stdbool.h>



// define a function pointer type that matches the STG calling convention
typedef void (*HsCall)(int64_t*, int64_t*, int64_t*, int64_t, int64_t, int64_t, int64_t,
                       int64_t, int64_t, int64_t*, float, float, float, float, double, double);

extern void
sipRound(
    int64_t* restrict baseReg,
    int64_t* restrict sp,
    int64_t* restrict hp,

    uint64_t v0, // R1
    uint64_t v1, // R2
    uint64_t v2, // R3
    uint64_t v3, // R4
    int64_t r5,
    int64_t r6,

    int64_t* restrict spLim,
    float f1,
    float f2,
    float f3,
    float f4,
    double d1,
    double d2)
{

    v0 += 1;
    v1 += 1;
    v2 += 1;
    v3 += 1;

    // create undefined variables, clang will emit these as a llvm undef literal
    const int64_t iUndef;
    const float fUndef;
    const double dUndef;

    const HsCall fun = (HsCall)sp[0];
    return fun(
            baseReg,
            sp,
            hp,

            v0,
            v1,
            v2,
            v3,
            iUndef,
            iUndef,

            spLim,
            fUndef,
            fUndef,
            fUndef,
            fUndef,
            dUndef,
            dUndef);
}

我真的不知道自己在做什么.有没有办法从该博客文章中调整技术？这是个坏主意吗？

Answer 1

如果你愿意手写汇编,你可以这样做(对于x86_64).将它放在带.s扩展名的文件中,并在ghc命令行中将其作为参数提供.

.global sipRound
sipRound:
    inc %rbx
    inc %r14
    inc %rsi
    inc %rdi
    jmp *(%rbp)

STG寄存器和机器寄存器之间的映射在https://github.com/ghc/ghc/blob/master/includes/stg/MachRegs.h#L159中定义.

请注意,仍然会涉及函数调用,因此它不如您从LLVM获取的代码有效.