libgo/go/reflect/makefunc_ffi.go

   1 // Copyright 2014 The Go Authors.  All rights reserved.
   2 // Use of this source code is governed by a BSD-style
   3 // license that can be found in the LICENSE file.
   4
   5 package reflect
   6
   7 import (
   8         "runtime"
   9         "unsafe"
  10 )
  11
  12 // The ffi function, written in C, allocates an FFI closure.  It
  13 // returns the code and data pointers.  When the code pointer is
  14 // called, it will call callback.  CIF is an FFI data structure
  15 // allocated as part of the closure, and is returned to ensure that
  16 // the GC retains it.
  17 func ffi(ftyp *funcType, callback func(unsafe.Pointer, unsafe.Pointer)) (code uintptr, data uintptr, cif unsafe.Pointer)
  18
  19 // The ffiFree function, written in C, releases the FFI closure.
  20 func ffiFree(uintptr)
  21
  22 // An ffiData holds the information needed to preserve an FFI closure
  23 // for the garbage collector.
  24 type ffiData struct {
  25         code     uintptr
  26         data     uintptr
  27         cif      unsafe.Pointer
  28         callback func(unsafe.Pointer, unsafe.Pointer)
  29 }
  30
  31 // The makeFuncFFI function uses libffi closures to implement
  32 // reflect.MakeFunc.  This is used for processors for which we don't
  33 // have more efficient support.
  34 func makeFuncFFI(ftyp *funcType, fn func(args []Value) (results []Value)) (uintptr, *ffiData) {
  35         callback := func(params, results unsafe.Pointer) {
  36                 ffiCall(ftyp, fn, params, results)
  37         }
  38
  39         code, data, cif := ffi(ftyp, callback)
  40
  41         c := &ffiData{code: code, data: data, cif: cif, callback: callback}
  42
  43         runtime.SetFinalizer(c,
  44                 func(p *ffiData) {
  45                         ffiFree(p.data)
  46                 })
  47
  48         return code, c
  49 }
  50
  51 // ffiCall takes pointers to the parameters, calls the function, and
  52 // stores the results back into memory.
  53 func ffiCall(ftyp *funcType, fn func([]Value) []Value, params unsafe.Pointer, results unsafe.Pointer) {
  54         in := make([]Value, 0, len(ftyp.in))
  55         ap := params
  56         for _, rt := range ftyp.in {
  57                 p := unsafe_New(rt)
  58                 memmove(p, *(*unsafe.Pointer)(ap), rt.size)
  59                 v := Value{rt, p, flag(rt.Kind()<<flagKindShift) | flagIndir}
  60                 in = append(in, v)
  61                 ap = (unsafe.Pointer)(uintptr(ap) + ptrSize)
  62         }
  63
  64         out := fn(in)
  65
  66         off := uintptr(0)
  67         for i, typ := range ftyp.out {
  68                 v := out[i]
  69                 if v.typ != typ {
  70                         panic("reflect: function created by MakeFunc using " + funcName(fn) +
  71                                 " returned wrong type: have " +
  72                                 out[i].typ.String() + " for " + typ.String())
  73                 }
  74                 if v.flag&flagRO != 0 {
  75                         panic("reflect: function created by MakeFunc using " + funcName(fn) +
  76                                 " returned value obtained from unexported field")
  77                 }
  78
  79                 off = align(off, uintptr(typ.fieldAlign))
  80                 addr := unsafe.Pointer(uintptr(results) + off)
  81                 if v.flag&flagIndir == 0 && (v.kind() == Ptr || v.kind() == UnsafePointer) {
  82                         *(*unsafe.Pointer)(addr) = v.ptr
  83                 } else {
  84                         memmove(addr, v.ptr, typ.size)
  85                 }
  86                 off += typ.size
  87         }
  88 }