1// SPDX-License-Identifier: Apache-2.0
2// SPDX-FileCopyrightText: 2022 The Ebitengine Authors
3
4//go:build darwin || freebsd || linux || windows
5
6package purego
7
8import (
9 "math"
10 "reflect"
11 "runtime"
12 "unsafe"
13
14 "github.com/ebitengine/purego/internal/strings"
15)
16
17// RegisterLibFunc is a wrapper around RegisterFunc that uses the C function returned from Dlsym(handle, name).
18// It panics if it can't find the name symbol.
19func RegisterLibFunc(fptr interface{}, handle uintptr, name string) {
20 sym, err := loadSymbol(handle, name)
21 if err != nil {
22 panic(err)
23 }
24 RegisterFunc(fptr, sym)
25}
26
27// RegisterFunc takes a pointer to a Go function representing the calling convention of the C function.
28// fptr will be set to a function that when called will call the C function given by cfn with the
29// parameters passed in the correct registers and stack.
30//
31// A panic is produced if the type is not a function pointer or if the function returns more than 1 value.
32//
33// These conversions describe how a Go type in the fptr will be used to call
34// the C function. It is important to note that there is no way to verify that fptr
35// matches the C function. This also holds true for struct types where the padding
36// needs to be ensured to match that of C; RegisterFunc does not verify this.
37//
38// # Type Conversions (Go <=> C)
39//
40// string <=> char*
41// bool <=> _Bool
42// uintptr <=> uintptr_t
43// uint <=> uint32_t or uint64_t
44// uint8 <=> uint8_t
45// uint16 <=> uint16_t
46// uint32 <=> uint32_t
47// uint64 <=> uint64_t
48// int <=> int32_t or int64_t
49// int8 <=> int8_t
50// int16 <=> int16_t
51// int32 <=> int32_t
52// int64 <=> int64_t
53// float32 <=> float (WIP)
54// float64 <=> double (WIP)
55// struct <=> struct (WIP)
56// func <=> C function
57// unsafe.Pointer, *T <=> void*
58// []T => void*
59//
60// There is a special case when the last argument of fptr is a variadic interface (or []interface}
61// it will be expanded into a call to the C function as if it had the arguments in that slice.
62// This means that using arg ...interface{} is like a cast to the function with the arguments inside arg.
63// This is not the same as C variadic.
64//
65// There are some limitations when using RegisterFunc on Linux. First, there is no support for function arguments.
66// Second, float32 and float64 arguments and return values do not work when CGO_ENABLED=1. Otherwise, Linux
67// has the same feature parity as Darwin.
68//
69// # Memory
70//
71// In general it is not possible for purego to guarantee the lifetimes of objects returned or received from
72// calling functions using RegisterFunc. For arguments to a C function it is important that the C function doesn't
73// hold onto a reference to Go memory. This is the same as the [Cgo rules].
74//
75// However, there are some special cases. When passing a string as an argument if the string does not end in a null
76// terminated byte (\x00) then the string will be copied into memory maintained by purego. The memory is only valid for
77// that specific call. Therefore, if the C code keeps a reference to that string it may become invalid at some
78// undefined time. However, if the string does already contain a null-terminated byte then no copy is done.
79// It is then the responsibility of the caller to ensure the string stays alive as long as it's needed in C memory.
80// This can be done using runtime.KeepAlive or allocating the string in C memory using malloc. When a C function
81// returns a null-terminated pointer to char a Go string can be used. Purego will allocate a new string in Go memory
82// and copy the data over. This string will be garbage collected whenever Go decides it's no longer referenced.
83// This C created string will not be freed by purego. If the pointer to char is not null-terminated or must continue
84// to point to C memory (because it's a buffer for example) then use a pointer to byte and then convert that to a slice
85// using unsafe.Slice. Doing this means that it becomes the responsibility of the caller to care about the lifetime
86// of the pointer
87//
88// # Example
89//
90// All functions below call this C function:
91//
92// char *foo(char *str);
93//
94// // Let purego convert types
95// var foo func(s string) string
96// goString := foo("copied")
97// // Go will garbage collect this string
98//
99// // Manually, handle allocations
100// var foo2 func(b string) *byte
101// mustFree := foo2("not copied\x00")
102// defer free(mustFree)
103//
104// [Cgo rules]: https://pkg.go.dev/cmd/cgo#hdr-Go_references_to_C
105func RegisterFunc(fptr interface{}, cfn uintptr) {
106 fn := reflect.ValueOf(fptr).Elem()
107 ty := fn.Type()
108 if ty.Kind() != reflect.Func {
109 panic("purego: fptr must be a function pointer")
110 }
111 if ty.NumOut() > 1 {
112 panic("purego: function can only return zero or one values")
113 }
114 if cfn == 0 {
115 panic("purego: cfn is nil")
116 }
117 {
118 // this code checks how many registers and stack this function will use
119 // to avoid crashing with too many arguments
120 var ints int
121 var floats int
122 var stack int
123 for i := 0; i < ty.NumIn(); i++ {
124 arg := ty.In(i)
125 switch arg.Kind() {
126 case reflect.String, reflect.Uintptr, reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64,
127 reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64, reflect.Ptr, reflect.UnsafePointer, reflect.Slice,
128 reflect.Func, reflect.Bool:
129 if ints < numOfIntegerRegisters() {
130 ints++
131 } else {
132 stack++
133 }
134 case reflect.Float32, reflect.Float64:
135 if floats < numOfFloats {
136 floats++
137 } else {
138 stack++
139 }
140 default:
141 panic("purego: unsupported kind " + arg.Kind().String())
142 }
143 }
144 sizeOfStack := maxArgs - numOfIntegerRegisters()
145 if stack > sizeOfStack {
146 panic("purego: too many arguments")
147 }
148 }
149 v := reflect.MakeFunc(ty, func(args []reflect.Value) (results []reflect.Value) {
150 if len(args) > 0 {
151 if variadic, ok := args[len(args)-1].Interface().([]interface{}); ok {
152 // subtract one from args bc the last argument in args is []interface{}
153 // which we are currently expanding
154 tmp := make([]reflect.Value, len(args)-1+len(variadic))
155 n := copy(tmp, args[:len(args)-1])
156 for i, v := range variadic {
157 tmp[n+i] = reflect.ValueOf(v)
158 }
159 args = tmp
160 }
161 }
162 var sysargs [maxArgs]uintptr
163 stack := sysargs[numOfIntegerRegisters():]
164 var floats [numOfFloats]uintptr
165 var numInts int
166 var numFloats int
167 var numStack int
168 var addStack, addInt, addFloat func(x uintptr)
169 if runtime.GOARCH == "arm64" || runtime.GOOS != "windows" {
170 // Windows arm64 uses the same calling convention as macOS and Linux
171 addStack = func(x uintptr) {
172 stack[numStack] = x
173 numStack++
174 }
175 addInt = func(x uintptr) {
176 if numInts >= numOfIntegerRegisters() {
177 addStack(x)
178 } else {
179 sysargs[numInts] = x
180 numInts++
181 }
182 }
183 addFloat = func(x uintptr) {
184 if numFloats < len(floats) {
185 floats[numFloats] = x
186 numFloats++
187 } else {
188 addStack(x)
189 }
190 }
191 } else {
192 // On Windows amd64 the arguments are passed in the numbered registered.
193 // So the first int is in the first integer register and the first float
194 // is in the second floating register if there is already a first int.
195 // This is in contrast to how macOS and Linux pass arguments which
196 // tries to use as many registers as possible in the calling convention.
197 addStack = func(x uintptr) {
198 sysargs[numStack] = x
199 numStack++
200 }
201 addInt = addStack
202 addFloat = addStack
203 }
204
205 var keepAlive []interface{}
206 defer func() {
207 runtime.KeepAlive(keepAlive)
208 runtime.KeepAlive(args)
209 }()
210 for _, v := range args {
211 switch v.Kind() {
212 case reflect.String:
213 ptr := strings.CString(v.String())
214 keepAlive = append(keepAlive, ptr)
215 addInt(uintptr(unsafe.Pointer(ptr)))
216 case reflect.Uintptr, reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
217 addInt(uintptr(v.Uint()))
218 case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
219 addInt(uintptr(v.Int()))
220 case reflect.Ptr, reflect.UnsafePointer, reflect.Slice:
221 // There is no need to keepAlive this pointer separately because it is kept alive in the args variable
222 addInt(v.Pointer())
223 case reflect.Func:
224 addInt(NewCallback(v.Interface()))
225 case reflect.Bool:
226 if v.Bool() {
227 addInt(1)
228 } else {
229 addInt(0)
230 }
231 case reflect.Float32:
232 addFloat(uintptr(math.Float32bits(float32(v.Float()))))
233 case reflect.Float64:
234 addFloat(uintptr(math.Float64bits(v.Float())))
235 default:
236 panic("purego: unsupported kind: " + v.Kind().String())
237 }
238 }
239 // TODO: support structs
240 var r1, r2 uintptr
241 if runtime.GOARCH == "arm64" || runtime.GOOS != "windows" {
242 // Use the normal arm64 calling convention even on Windows
243 syscall := syscall9Args{
244 cfn,
245 sysargs[0], sysargs[1], sysargs[2], sysargs[3], sysargs[4], sysargs[5], sysargs[6], sysargs[7], sysargs[8],
246 floats[0], floats[1], floats[2], floats[3], floats[4], floats[5], floats[6], floats[7],
247 0, 0, 0,
248 }
249 runtime_cgocall(syscall9XABI0, unsafe.Pointer(&syscall))
250 r1, r2 = syscall.r1, syscall.r2
251 } else {
252 // This is a fallback for amd64, 386, and arm. Note this may not support floats
253 r1, r2, _ = syscall_syscall9X(cfn, sysargs[0], sysargs[1], sysargs[2], sysargs[3], sysargs[4], sysargs[5], sysargs[6], sysargs[7], sysargs[8])
254 }
255 if ty.NumOut() == 0 {
256 return nil
257 }
258 outType := ty.Out(0)
259 v := reflect.New(outType).Elem()
260 switch outType.Kind() {
261 case reflect.Uintptr, reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
262 v.SetUint(uint64(r1))
263 case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
264 v.SetInt(int64(r1))
265 case reflect.Bool:
266 v.SetBool(r1 != 0)
267 case reflect.UnsafePointer:
268 // We take the address and then dereference it to trick go vet from creating a possible miss-use of unsafe.Pointer
269 v.SetPointer(*(*unsafe.Pointer)(unsafe.Pointer(&r1)))
270 case reflect.Ptr:
271 // It is safe to have the address of r1 not escape because it is immediately dereferenced with .Elem()
272 v = reflect.NewAt(outType, runtime_noescape(unsafe.Pointer(&r1))).Elem()
273 case reflect.Func:
274 // wrap this C function in a nicely typed Go function
275 v = reflect.New(outType)
276 RegisterFunc(v.Interface(), r1)
277 case reflect.String:
278 v.SetString(strings.GoString(r1))
279 case reflect.Float32, reflect.Float64:
280 // NOTE: r2 is only the floating return value on 64bit platforms.
281 // On 32bit platforms r2 is the upper part of a 64bit return.
282 v.SetFloat(math.Float64frombits(uint64(r2)))
283 default:
284 panic("purego: unsupported return kind: " + outType.Kind().String())
285 }
286 return []reflect.Value{v}
287 })
288 fn.Set(v)
289}
290
291func numOfIntegerRegisters() int {
292 switch runtime.GOARCH {
293 case "arm64":
294 return 8
295 case "amd64":
296 return 6
297 // TODO: figure out why 386 tests are not working
298 /*case "386":
299 return 0
300 case "arm":
301 return 4*/
302 default:
303 panic("purego: unknown GOARCH (" + runtime.GOARCH + ")")
304 }
305}