为什么没有'外国进口原料不安全'？ [英] Why is there no 'foreign import prim unsafe'?

问题描述

这是我之前提出的问题的一个后续步骤这里。我已经能够根据 Reid Barton的回答得到一些结果，但我注意到在核心中我看到 __ pkg_ccall_GC ：

  case {__pkg_ccall_GC hashabler-2.0.0 sipRound_s_x2 Word＃
 - > Word＃
  - > Word＃
  - > Word＃
  - > （＃Word＃，Word＃，Word＃，Word＃＃）} 
 ww1 ww2 ww3（xor＃ww4 b1）
  

我认为您对安全ffi呼叫的期望是什么。然而，将不安全添加到外部导入字符串是不允许的（尽管错误消息没有说明原因）：

  src /Data/Hashabler/SipHash.hs:60:1：error：
•安全/不安全批注不应与`foreign import prim'一起使用。 
•检查声明时：
国外进口原料不安全静态sipRound_s_x4sipRound_s_x4＃
 :: Word＃
  - >单词＃ - >单词＃ - >单词＃ - > （＃Word＃，Word＃，Word＃，Word＃＃）
  

我的外国程序只是一个一点点，但有点扭曲，所以我不认为我想要什么 _GC 给我。我看过的GHC源代码的一些相关位，FWIW和background：

编译器/前奏/ ForeignCall.hs：只有Risky省略了_GC

 数据安全性
 = PlaySafe  - 可以调用Haskell GC，或者进行回调或
  - 切换线程等。因此，在通话之前确保事情是
  -  tidy。此外，在线程
  -  RTS中，我们安排外部调用被执行
  - 由单独的OS线程执行，即_concurrently_到
  - 执行其他Haskell线程。 
 
 | PlayInterruptible  - 与PlaySafe一样，但另外
  - 运行此外部调用的工作线程可能
  - 会被不必要地终止，因此必须在未绑定的线程上调度
。 
 
 | PlayRisky  - 以上都不会发生;该调用将返回
  - 不与所有运行时系统交互
派生（Eq，Show，Data）
  - 仅用于显示Lex.Token的显示，我认为
  

我还看到一些外部import prim unsafe 和 ... safe 在GHC树中，但我认为它是死代码。例如 testsuite / tests / printer / Ppr046.hs 。

所以我的问题是：

1. 从 __ pkg_ccall_GC 与a __ pkg_ccall 在这种情况下（我在做 foreign import prim 不是 ccall ）？是否与 here 中描述的相同？


2. 为什么不是 foreign import unsafe 似乎被支持吗？


3. 假设我明白了（1）：有没有我可以工作的（1）？
   





---

$ b是否有效地返回多个值并避免发生$ b

编辑：从 -ddump-asm 查看程序集清楚地说明没有任何事情发生（不应该有人害怕看看大会），支持雷德巴顿的评论如下：

  movq％rdi，％rax 
 movq％r8 ，％rdi 
 xorq％r9，％rdi 
 movq％rsi，％rcx 
 movq％rax，％rsi 
 movq％r14，％rax 
 movq％rcx ，％r14 
 movq％rbx，％rcx 
 movq％rax，％rbx 
 movq％r9，-8（％rbp）
 movq％rcx，（％rbp）
 addq $ -16，％rbp 
 jmp sipRound_s_x2 
  

向上的 xorq 对应于haskell xor 。所有这些 movq 似乎都是一件坏事，尽管...

正如里德巴顿指出的 __ pkg_ccall_GC 不表示任何东西。生成的代码不会执行您在 safe FFI调用中看到的簿记。

This is a followup to my earlier question here. I've been able to get something working per Reid Barton's answer, but I notice in the core I see __pkg_ccall_GC:

              case {__pkg_ccall_GC hashabler-2.0.0 sipRound_s_x2 Word#
                                          -> Word#
                                          -> Word#
                                          -> Word#
                                          -> (# Word#, Word#, Word#, Word# #)}
                     ww1 ww2 ww3 (xor# ww4 b1)

Which is I think what you'd expect for a "safe" ffi call. Yet adding "unsafe" to the foreign import string is not allowed (though the error messages doesn't say why):

src/Data/Hashabler/SipHash.hs:60:1: error:
    • The safe/unsafe annotation should not be used with `foreign import prim'.
    • When checking declaration:
        foreign import prim unsafe "static sipRound_s_x4" sipRound_s_x4#
          :: Word#
             -> Word# -> Word# -> Word# -> (# Word#, Word#, Word#, Word# #)

My foreign procedure is just a little but of bit-twiddling, so I don't think I want whatever the _GC is giving me. Some relevant bits of GHC source I've looked at, FWIW and background:

compiler/prelude/ForeignCall.hs: only "Risky" omits the "_GC"

data Safety
  = PlaySafe            -- Might invoke Haskell GC, or do a call back, or
                        -- switch threads, etc.  So make sure things are
                        -- tidy before the call. Additionally, in the threaded
                        -- RTS we arrange for the external call to be executed
                        -- by a separate OS thread, i.e., _concurrently_ to the
                        -- execution of other Haskell threads.

  | PlayInterruptible   -- Like PlaySafe, but additionally
                        -- the worker thread running this foreign call may
                        -- be unceremoniously killed, so it must be scheduled
                        -- on an unbound thread.

  | PlayRisky           -- None of the above can happen; the call will return
                        -- without interacting with the runtime system at all
  deriving ( Eq, Show, Data )
        -- Show used just for Show Lex.Token, I think

I also see some foreign import prim unsafe and ... safe in the GHC tree, though I suppose it's dead code. e.g. testsuite/tests/printer/Ppr046.hs.

So my questions are:

1. What is the difference between code generated from a __pkg_ccall_GC vs a __pkg_ccall in this case (where I'm doing foreign import prim not ccall)? Is it the same as described here?
2. Why doesn't a foreign import prim unsafe seem to be supported?
3. Assuming I understand (1): Is there anyway I can work around this, getting both efficient return of multiple values and avoiding whatever bookkeeping is happening in (1)?

---

EDIT: Looking at the assembly from -ddump-asm makes it clear nothing much is happening (shouldn't have been scared to look at the assembly), support Reid Barton's comment below:

movq %rdi,%rax
movq %r8,%rdi 
xorq %r9,%rdi
movq %rsi,%rcx
movq %rax,%rsi
movq %r14,%rax
movq %rcx,%r14
movq %rbx,%rcx
movq %rax,%rbx
movq %r9,-8(%rbp)
movq %rcx,(%rbp)
addq $-16,%rbp
jmp sipRound_s_x2

The xorq towards the top corresponds to a haskell xor. All those movq do seem to be a bummer though...

解决方案

As Reid Barton points out the __pkg_ccall_GC doesn't indicate anything. The code generated doesn't do the bookkeeping you would see in a safe FFI call.

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