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 "fmt"
10 "math"
11 "reflect"
12 "runtime"
13 "sync"
14 "unsafe"
15
16 "github.com/ebitengine/purego/internal/strings"
17)
18
19var thePool = sync.Pool{New: func() any {
20 return new(syscall15Args)
21}}
22
23// RegisterLibFunc is a wrapper around RegisterFunc that uses the C function returned from Dlsym(handle, name).
24// It panics if it can't find the name symbol.
25func RegisterLibFunc(fptr any, handle uintptr, name string) {
26 sym, err := loadSymbol(handle, name)
27 if err != nil {
28 panic(err)
29 }
30 RegisterFunc(fptr, sym)
31}
32
33// RegisterFunc takes a pointer to a Go function representing the calling convention of the C function.
34// fptr will be set to a function that when called will call the C function given by cfn with the
35// parameters passed in the correct registers and stack.
36//
37// A panic is produced if the type is not a function pointer or if the function returns more than 1 value.
38//
39// These conversions describe how a Go type in the fptr will be used to call
40// the C function. It is important to note that there is no way to verify that fptr
41// matches the C function. This also holds true for struct types where the padding
42// needs to be ensured to match that of C; RegisterFunc does not verify this.
43//
44// # Type Conversions (Go <=> C)
45//
46// string <=> char*
47// bool <=> _Bool
48// uintptr <=> uintptr_t
49// uint <=> uint32_t or uint64_t
50// uint8 <=> uint8_t
51// uint16 <=> uint16_t
52// uint32 <=> uint32_t
53// uint64 <=> uint64_t
54// int <=> int32_t or int64_t
55// int8 <=> int8_t
56// int16 <=> int16_t
57// int32 <=> int32_t
58// int64 <=> int64_t
59// float32 <=> float
60// float64 <=> double
61// struct <=> struct (WIP - darwin only)
62// func <=> C function
63// unsafe.Pointer, *T <=> void*
64// []T => void*
65//
66// There is a special case when the last argument of fptr is a variadic interface (or []interface}
67// it will be expanded into a call to the C function as if it had the arguments in that slice.
68// This means that using arg ...any is like a cast to the function with the arguments inside arg.
69// This is not the same as C variadic.
70//
71// # Memory
72//
73// In general it is not possible for purego to guarantee the lifetimes of objects returned or received from
74// calling functions using RegisterFunc. For arguments to a C function it is important that the C function doesn't
75// hold onto a reference to Go memory. This is the same as the [Cgo rules].
76//
77// However, there are some special cases. When passing a string as an argument if the string does not end in a null
78// terminated byte (\x00) then the string will be copied into memory maintained by purego. The memory is only valid for
79// that specific call. Therefore, if the C code keeps a reference to that string it may become invalid at some
80// undefined time. However, if the string does already contain a null-terminated byte then no copy is done.
81// It is then the responsibility of the caller to ensure the string stays alive as long as it's needed in C memory.
82// This can be done using runtime.KeepAlive or allocating the string in C memory using malloc. When a C function
83// returns a null-terminated pointer to char a Go string can be used. Purego will allocate a new string in Go memory
84// and copy the data over. This string will be garbage collected whenever Go decides it's no longer referenced.
85// This C created string will not be freed by purego. If the pointer to char is not null-terminated or must continue
86// 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
87// using unsafe.Slice. Doing this means that it becomes the responsibility of the caller to care about the lifetime
88// of the pointer
89//
90// # Structs
91//
92// Purego can handle the most common structs that have fields of builtin types like int8, uint16, float32, etc. However,
93// it does not support aligning fields properly. It is therefore the responsibility of the caller to ensure
94// that all padding is added to the Go struct to match the C one. See `BoolStructFn` in struct_test.go for an example.
95//
96// # Example
97//
98// All functions below call this C function:
99//
100// char *foo(char *str);
101//
102// // Let purego convert types
103// var foo func(s string) string
104// goString := foo("copied")
105// // Go will garbage collect this string
106//
107// // Manually, handle allocations
108// var foo2 func(b string) *byte
109// mustFree := foo2("not copied\x00")
110// defer free(mustFree)
111//
112// [Cgo rules]: https://pkg.go.dev/cmd/cgo#hdr-Go_references_to_C
113func RegisterFunc(fptr any, cfn uintptr) {
114 fn := reflect.ValueOf(fptr).Elem()
115 ty := fn.Type()
116 if ty.Kind() != reflect.Func {
117 panic("purego: fptr must be a function pointer")
118 }
119 if ty.NumOut() > 1 {
120 panic("purego: function can only return zero or one values")
121 }
122 if cfn == 0 {
123 panic("purego: cfn is nil")
124 }
125 if ty.NumOut() == 1 && (ty.Out(0).Kind() == reflect.Float32 || ty.Out(0).Kind() == reflect.Float64) &&
126 runtime.GOARCH != "arm64" && runtime.GOARCH != "amd64" {
127 panic("purego: float returns are not supported")
128 }
129 {
130 // this code checks how many registers and stack this function will use
131 // to avoid crashing with too many arguments
132 var ints int
133 var floats int
134 var stack int
135 for i := 0; i < ty.NumIn(); i++ {
136 arg := ty.In(i)
137 switch arg.Kind() {
138 case reflect.Func:
139 // This only does preliminary testing to ensure the CDecl argument
140 // is the first argument. Full testing is done when the callback is actually
141 // created in NewCallback.
142 for j := 0; j < arg.NumIn(); j++ {
143 in := arg.In(j)
144 if !in.AssignableTo(reflect.TypeOf(CDecl{})) {
145 continue
146 }
147 if j != 0 {
148 panic("purego: CDecl must be the first argument")
149 }
150 }
151 case reflect.String, reflect.Uintptr, reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64,
152 reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64, reflect.Ptr, reflect.UnsafePointer,
153 reflect.Slice, reflect.Bool:
154 if ints < numOfIntegerRegisters() {
155 ints++
156 } else {
157 stack++
158 }
159 case reflect.Float32, reflect.Float64:
160 const is32bit = unsafe.Sizeof(uintptr(0)) == 4
161 if is32bit {
162 panic("purego: floats only supported on 64bit platforms")
163 }
164 if floats < numOfFloats {
165 floats++
166 } else {
167 stack++
168 }
169 case reflect.Struct:
170 if runtime.GOOS != "darwin" || (runtime.GOARCH != "amd64" && runtime.GOARCH != "arm64") {
171 panic("purego: struct arguments are only supported on darwin amd64 & arm64")
172 }
173 if arg.Size() == 0 {
174 continue
175 }
176 addInt := func(u uintptr) {
177 ints++
178 }
179 addFloat := func(u uintptr) {
180 floats++
181 }
182 addStack := func(u uintptr) {
183 stack++
184 }
185 _ = addStruct(reflect.New(arg).Elem(), &ints, &floats, &stack, addInt, addFloat, addStack, nil)
186 default:
187 panic("purego: unsupported kind " + arg.Kind().String())
188 }
189 }
190 if ty.NumOut() == 1 && ty.Out(0).Kind() == reflect.Struct {
191 if runtime.GOOS != "darwin" {
192 panic("purego: struct return values only supported on darwin arm64 & amd64")
193 }
194 outType := ty.Out(0)
195 checkStructFieldsSupported(outType)
196 if runtime.GOARCH == "amd64" && outType.Size() > maxRegAllocStructSize {
197 // on amd64 if struct is bigger than 16 bytes allocate the return struct
198 // and pass it in as a hidden first argument.
199 ints++
200 }
201 }
202 sizeOfStack := maxArgs - numOfIntegerRegisters()
203 if stack > sizeOfStack {
204 panic("purego: too many arguments")
205 }
206 }
207 v := reflect.MakeFunc(ty, func(args []reflect.Value) (results []reflect.Value) {
208 var sysargs [maxArgs]uintptr
209 stack := sysargs[numOfIntegerRegisters():]
210 var floats [numOfFloats]uintptr
211 var numInts int
212 var numFloats int
213 var numStack int
214 var addStack, addInt, addFloat func(x uintptr)
215 if runtime.GOARCH == "arm64" || runtime.GOOS != "windows" {
216 // Windows arm64 uses the same calling convention as macOS and Linux
217 addStack = func(x uintptr) {
218 stack[numStack] = x
219 numStack++
220 }
221 addInt = func(x uintptr) {
222 if numInts >= numOfIntegerRegisters() {
223 addStack(x)
224 } else {
225 sysargs[numInts] = x
226 numInts++
227 }
228 }
229 addFloat = func(x uintptr) {
230 if numFloats < len(floats) {
231 floats[numFloats] = x
232 numFloats++
233 } else {
234 addStack(x)
235 }
236 }
237 } else {
238 // On Windows amd64 the arguments are passed in the numbered registered.
239 // So the first int is in the first integer register and the first float
240 // is in the second floating register if there is already a first int.
241 // This is in contrast to how macOS and Linux pass arguments which
242 // tries to use as many registers as possible in the calling convention.
243 addStack = func(x uintptr) {
244 sysargs[numStack] = x
245 numStack++
246 }
247 addInt = addStack
248 addFloat = addStack
249 }
250
251 var keepAlive []any
252 defer func() {
253 runtime.KeepAlive(keepAlive)
254 runtime.KeepAlive(args)
255 }()
256
257 var arm64_r8 uintptr
258 if ty.NumOut() == 1 && ty.Out(0).Kind() == reflect.Struct {
259 outType := ty.Out(0)
260 if runtime.GOARCH == "amd64" && outType.Size() > maxRegAllocStructSize {
261 val := reflect.New(outType)
262 keepAlive = append(keepAlive, val)
263 addInt(val.Pointer())
264 } else if runtime.GOARCH == "arm64" && outType.Size() > maxRegAllocStructSize {
265 isAllFloats, numFields := isAllSameFloat(outType)
266 if !isAllFloats || numFields > 4 {
267 val := reflect.New(outType)
268 keepAlive = append(keepAlive, val)
269 arm64_r8 = val.Pointer()
270 }
271 }
272 }
273 for i, v := range args {
274 if variadic, ok := args[i].Interface().([]any); ok {
275 if i != len(args)-1 {
276 panic("purego: can only expand last parameter")
277 }
278 for _, x := range variadic {
279 keepAlive = addValue(reflect.ValueOf(x), keepAlive, addInt, addFloat, addStack, &numInts, &numFloats, &numStack)
280 }
281 continue
282 }
283 keepAlive = addValue(v, keepAlive, addInt, addFloat, addStack, &numInts, &numFloats, &numStack)
284 }
285
286 syscall := thePool.Get().(*syscall15Args)
287 defer thePool.Put(syscall)
288
289 if runtime.GOARCH == "arm64" || runtime.GOOS != "windows" {
290 // Use the normal arm64 calling convention even on Windows
291 *syscall = syscall15Args{
292 cfn,
293 sysargs[0], sysargs[1], sysargs[2], sysargs[3], sysargs[4], sysargs[5],
294 sysargs[6], sysargs[7], sysargs[8], sysargs[9], sysargs[10], sysargs[11],
295 sysargs[12], sysargs[13], sysargs[14],
296 floats[0], floats[1], floats[2], floats[3], floats[4], floats[5], floats[6], floats[7],
297 arm64_r8,
298 }
299 runtime_cgocall(syscall15XABI0, unsafe.Pointer(syscall))
300 } else {
301 *syscall = syscall15Args{}
302 // This is a fallback for Windows amd64, 386, and arm. Note this may not support floats
303 syscall.a1, syscall.a2, _ = syscall_syscall15X(cfn, sysargs[0], sysargs[1], sysargs[2], sysargs[3], sysargs[4],
304 sysargs[5], sysargs[6], sysargs[7], sysargs[8], sysargs[9], sysargs[10], sysargs[11],
305 sysargs[12], sysargs[13], sysargs[14])
306 syscall.f1 = syscall.a2 // on amd64 a2 stores the float return. On 32bit platforms floats aren't support
307 }
308 if ty.NumOut() == 0 {
309 return nil
310 }
311 outType := ty.Out(0)
312 v := reflect.New(outType).Elem()
313 switch outType.Kind() {
314 case reflect.Uintptr, reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
315 v.SetUint(uint64(syscall.a1))
316 case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
317 v.SetInt(int64(syscall.a1))
318 case reflect.Bool:
319 v.SetBool(byte(syscall.a1) != 0)
320 case reflect.UnsafePointer:
321 // We take the address and then dereference it to trick go vet from creating a possible miss-use of unsafe.Pointer
322 v.SetPointer(*(*unsafe.Pointer)(unsafe.Pointer(&syscall.a1)))
323 case reflect.Ptr:
324 v = reflect.NewAt(outType, unsafe.Pointer(&syscall.a1)).Elem()
325 case reflect.Func:
326 // wrap this C function in a nicely typed Go function
327 v = reflect.New(outType)
328 RegisterFunc(v.Interface(), syscall.a1)
329 case reflect.String:
330 v.SetString(strings.GoString(syscall.a1))
331 case reflect.Float32:
332 // NOTE: syscall.r2 is only the floating return value on 64bit platforms.
333 // On 32bit platforms syscall.r2 is the upper part of a 64bit return.
334 v.SetFloat(float64(math.Float32frombits(uint32(syscall.f1))))
335 case reflect.Float64:
336 // NOTE: syscall.r2 is only the floating return value on 64bit platforms.
337 // On 32bit platforms syscall.r2 is the upper part of a 64bit return.
338 v.SetFloat(math.Float64frombits(uint64(syscall.f1)))
339 case reflect.Struct:
340 v = getStruct(outType, *syscall)
341 default:
342 panic("purego: unsupported return kind: " + outType.Kind().String())
343 }
344 if len(args) > 0 {
345 // reuse args slice instead of allocating one when possible
346 args[0] = v
347 return args[:1]
348 } else {
349 return []reflect.Value{v}
350 }
351 })
352 fn.Set(v)
353}
354
355func addValue(v reflect.Value, keepAlive []any, addInt func(x uintptr), addFloat func(x uintptr), addStack func(x uintptr), numInts *int, numFloats *int, numStack *int) []any {
356 switch v.Kind() {
357 case reflect.String:
358 ptr := strings.CString(v.String())
359 keepAlive = append(keepAlive, ptr)
360 addInt(uintptr(unsafe.Pointer(ptr)))
361 case reflect.Uintptr, reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
362 addInt(uintptr(v.Uint()))
363 case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
364 addInt(uintptr(v.Int()))
365 case reflect.Ptr, reflect.UnsafePointer, reflect.Slice:
366 // There is no need to keepAlive this pointer separately because it is kept alive in the args variable
367 addInt(v.Pointer())
368 case reflect.Func:
369 addInt(NewCallback(v.Interface()))
370 case reflect.Bool:
371 if v.Bool() {
372 addInt(1)
373 } else {
374 addInt(0)
375 }
376 case reflect.Float32:
377 addFloat(uintptr(math.Float32bits(float32(v.Float()))))
378 case reflect.Float64:
379 addFloat(uintptr(math.Float64bits(v.Float())))
380 case reflect.Struct:
381 keepAlive = addStruct(v, numInts, numFloats, numStack, addInt, addFloat, addStack, keepAlive)
382 default:
383 panic("purego: unsupported kind: " + v.Kind().String())
384 }
385 return keepAlive
386}
387
388// maxRegAllocStructSize is the biggest a struct can be while still fitting in registers.
389// if it is bigger than this than enough space must be allocated on the heap and then passed into
390// the function as the first parameter on amd64 or in R8 on arm64.
391//
392// If you change this make sure to update it in objc_runtime_darwin.go
393const maxRegAllocStructSize = 16
394
395func isAllSameFloat(ty reflect.Type) (allFloats bool, numFields int) {
396 allFloats = true
397 root := ty.Field(0).Type
398 for root.Kind() == reflect.Struct {
399 root = root.Field(0).Type
400 }
401 first := root.Kind()
402 if first != reflect.Float32 && first != reflect.Float64 {
403 allFloats = false
404 }
405 for i := 0; i < ty.NumField(); i++ {
406 f := ty.Field(i).Type
407 if f.Kind() == reflect.Struct {
408 var structNumFields int
409 allFloats, structNumFields = isAllSameFloat(f)
410 numFields += structNumFields
411 continue
412 }
413 numFields++
414 if f.Kind() != first {
415 allFloats = false
416 }
417 }
418 return allFloats, numFields
419}
420
421func checkStructFieldsSupported(ty reflect.Type) {
422 for i := 0; i < ty.NumField(); i++ {
423 f := ty.Field(i).Type
424 if f.Kind() == reflect.Array {
425 f = f.Elem()
426 } else if f.Kind() == reflect.Struct {
427 checkStructFieldsSupported(f)
428 continue
429 }
430 switch f.Kind() {
431 case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64,
432 reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64,
433 reflect.Uintptr, reflect.Ptr, reflect.UnsafePointer, reflect.Float64, reflect.Float32:
434 default:
435 panic(fmt.Sprintf("purego: struct field type %s is not supported", f))
436 }
437 }
438}
439
440func roundUpTo8(val uintptr) uintptr {
441 return (val + 7) &^ 7
442}
443
444func numOfIntegerRegisters() int {
445 switch runtime.GOARCH {
446 case "arm64":
447 return 8
448 case "amd64":
449 return 6
450 default:
451 // since this platform isn't supported and can therefore only access
452 // integer registers it is fine to return the maxArgs
453 return maxArgs
454 }
455}