1// SPDX-License-Identifier: Apache-2.0
2// SPDX-FileCopyrightText: 2022 The Ebitengine Authors
3
4//go:build darwin || freebsd || linux || netbsd || windows
5
6package purego
7
8import (
9 "fmt"
10 "math"
11 "reflect"
12 "runtime"
13 "strconv"
14 "sync"
15 "unsafe"
16
17 "github.com/ebitengine/purego/internal/strings"
18)
19
20var thePool = sync.Pool{New: func() any {
21 return new(syscall15Args)
22}}
23
24// RegisterLibFunc is a wrapper around RegisterFunc that uses the C function returned from Dlsym(handle, name).
25// It panics if it can't find the name symbol.
26func RegisterLibFunc(fptr any, handle uintptr, name string) {
27 sym, err := loadSymbol(handle, name)
28 if err != nil {
29 panic(err)
30 }
31 RegisterFunc(fptr, sym)
32}
33
34// RegisterFunc takes a pointer to a Go function representing the calling convention of the C function.
35// fptr will be set to a function that when called will call the C function given by cfn with the
36// parameters passed in the correct registers and stack.
37//
38// A panic is produced if the type is not a function pointer or if the function returns more than 1 value.
39//
40// These conversions describe how a Go type in the fptr will be used to call
41// the C function. It is important to note that there is no way to verify that fptr
42// matches the C function. This also holds true for struct types where the padding
43// needs to be ensured to match that of C; RegisterFunc does not verify this.
44//
45// # Type Conversions (Go <=> C)
46//
47// string <=> char*
48// bool <=> _Bool
49// uintptr <=> uintptr_t
50// uint <=> uint32_t or uint64_t
51// uint8 <=> uint8_t
52// uint16 <=> uint16_t
53// uint32 <=> uint32_t
54// uint64 <=> uint64_t
55// int <=> int32_t or int64_t
56// int8 <=> int8_t
57// int16 <=> int16_t
58// int32 <=> int32_t
59// int64 <=> int64_t
60// float32 <=> float
61// float64 <=> double
62// struct <=> struct (WIP - darwin only)
63// func <=> C function
64// unsafe.Pointer, *T <=> void*
65// []T => void*
66//
67// There is a special case when the last argument of fptr is a variadic interface (or []interface}
68// it will be expanded into a call to the C function as if it had the arguments in that slice.
69// This means that using arg ...any is like a cast to the function with the arguments inside arg.
70// This is not the same as C variadic.
71//
72// # Memory
73//
74// In general it is not possible for purego to guarantee the lifetimes of objects returned or received from
75// calling functions using RegisterFunc. For arguments to a C function it is important that the C function doesn't
76// hold onto a reference to Go memory. This is the same as the [Cgo rules].
77//
78// However, there are some special cases. When passing a string as an argument if the string does not end in a null
79// terminated byte (\x00) then the string will be copied into memory maintained by purego. The memory is only valid for
80// that specific call. Therefore, if the C code keeps a reference to that string it may become invalid at some
81// undefined time. However, if the string does already contain a null-terminated byte then no copy is done.
82// It is then the responsibility of the caller to ensure the string stays alive as long as it's needed in C memory.
83// This can be done using runtime.KeepAlive or allocating the string in C memory using malloc. When a C function
84// returns a null-terminated pointer to char a Go string can be used. Purego will allocate a new string in Go memory
85// and copy the data over. This string will be garbage collected whenever Go decides it's no longer referenced.
86// This C created string will not be freed by purego. If the pointer to char is not null-terminated or must continue
87// 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
88// using unsafe.Slice. Doing this means that it becomes the responsibility of the caller to care about the lifetime
89// of the pointer
90//
91// # Structs
92//
93// Purego can handle the most common structs that have fields of builtin types like int8, uint16, float32, etc. However,
94// it does not support aligning fields properly. It is therefore the responsibility of the caller to ensure
95// that all padding is added to the Go struct to match the C one. See `BoolStructFn` in struct_test.go for an example.
96//
97// # Example
98//
99// All functions below call this C function:
100//
101// char *foo(char *str);
102//
103// // Let purego convert types
104// var foo func(s string) string
105// goString := foo("copied")
106// // Go will garbage collect this string
107//
108// // Manually, handle allocations
109// var foo2 func(b string) *byte
110// mustFree := foo2("not copied\x00")
111// defer free(mustFree)
112//
113// [Cgo rules]: https://pkg.go.dev/cmd/cgo#hdr-Go_references_to_C
114func RegisterFunc(fptr any, cfn uintptr) {
115 fn := reflect.ValueOf(fptr).Elem()
116 ty := fn.Type()
117 if ty.Kind() != reflect.Func {
118 panic("purego: fptr must be a function pointer")
119 }
120 if ty.NumOut() > 1 {
121 panic("purego: function can only return zero or one values")
122 }
123 if cfn == 0 {
124 panic("purego: cfn is nil")
125 }
126 if ty.NumOut() == 1 && (ty.Out(0).Kind() == reflect.Float32 || ty.Out(0).Kind() == reflect.Float64) &&
127 runtime.GOARCH != "arm64" && runtime.GOARCH != "amd64" {
128 panic("purego: float returns are not supported")
129 }
130 {
131 // this code checks how many registers and stack this function will use
132 // to avoid crashing with too many arguments
133 var ints int
134 var floats int
135 var stack int
136 for i := 0; i < ty.NumIn(); i++ {
137 arg := ty.In(i)
138 switch arg.Kind() {
139 case reflect.Func:
140 // This only does preliminary testing to ensure the CDecl argument
141 // is the first argument. Full testing is done when the callback is actually
142 // created in NewCallback.
143 for j := 0; j < arg.NumIn(); j++ {
144 in := arg.In(j)
145 if !in.AssignableTo(reflect.TypeOf(CDecl{})) {
146 continue
147 }
148 if j != 0 {
149 panic("purego: CDecl must be the first argument")
150 }
151 }
152 case reflect.String, reflect.Uintptr, reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64,
153 reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64, reflect.Ptr, reflect.UnsafePointer,
154 reflect.Slice, reflect.Bool:
155 if ints < numOfIntegerRegisters() {
156 ints++
157 } else {
158 stack++
159 }
160 case reflect.Float32, reflect.Float64:
161 const is32bit = unsafe.Sizeof(uintptr(0)) == 4
162 if is32bit {
163 panic("purego: floats only supported on 64bit platforms")
164 }
165 if floats < numOfFloatRegisters {
166 floats++
167 } else {
168 stack++
169 }
170 case reflect.Struct:
171 if runtime.GOOS != "darwin" || (runtime.GOARCH != "amd64" && runtime.GOARCH != "arm64") {
172 panic("purego: struct arguments are only supported on darwin amd64 & arm64")
173 }
174 if arg.Size() == 0 {
175 continue
176 }
177 addInt := func(u uintptr) {
178 ints++
179 }
180 addFloat := func(u uintptr) {
181 floats++
182 }
183 addStack := func(u uintptr) {
184 stack++
185 }
186 _ = addStruct(reflect.New(arg).Elem(), &ints, &floats, &stack, addInt, addFloat, addStack, nil)
187 default:
188 panic("purego: unsupported kind " + arg.Kind().String())
189 }
190 }
191 if ty.NumOut() == 1 && ty.Out(0).Kind() == reflect.Struct {
192 if runtime.GOOS != "darwin" {
193 panic("purego: struct return values only supported on darwin arm64 & amd64")
194 }
195 outType := ty.Out(0)
196 checkStructFieldsSupported(outType)
197 if runtime.GOARCH == "amd64" && outType.Size() > maxRegAllocStructSize {
198 // on amd64 if struct is bigger than 16 bytes allocate the return struct
199 // and pass it in as a hidden first argument.
200 ints++
201 }
202 }
203 sizeOfStack := maxArgs - numOfIntegerRegisters()
204 if stack > sizeOfStack {
205 panic("purego: too many arguments")
206 }
207 }
208 v := reflect.MakeFunc(ty, func(args []reflect.Value) (results []reflect.Value) {
209 var sysargs [maxArgs]uintptr
210 var floats [numOfFloatRegisters]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 sysargs[numOfIntegerRegisters()+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 if runtime.GOARCH == "arm64" && runtime.GOOS == "darwin" &&
284 (numInts >= numOfIntegerRegisters() || numFloats >= numOfFloatRegisters) && v.Kind() != reflect.Struct { // hit the stack
285 fields := make([]reflect.StructField, len(args[i:]))
286
287 for j, val := range args[i:] {
288 if val.Kind() == reflect.String {
289 ptr := strings.CString(v.String())
290 keepAlive = append(keepAlive, ptr)
291 val = reflect.ValueOf(ptr)
292 args[i+j] = val
293 }
294 fields[j] = reflect.StructField{
295 Name: "X" + strconv.Itoa(j),
296 Type: val.Type(),
297 }
298 }
299 structType := reflect.StructOf(fields)
300 structInstance := reflect.New(structType).Elem()
301 for j, val := range args[i:] {
302 structInstance.Field(j).Set(val)
303 }
304 placeRegisters(structInstance, addFloat, addInt)
305 break
306 }
307 keepAlive = addValue(v, keepAlive, addInt, addFloat, addStack, &numInts, &numFloats, &numStack)
308 }
309
310 syscall := thePool.Get().(*syscall15Args)
311 defer thePool.Put(syscall)
312
313 if runtime.GOARCH == "arm64" || runtime.GOOS != "windows" {
314 // Use the normal arm64 calling convention even on Windows
315 *syscall = syscall15Args{
316 cfn,
317 sysargs[0], sysargs[1], sysargs[2], sysargs[3], sysargs[4], sysargs[5],
318 sysargs[6], sysargs[7], sysargs[8], sysargs[9], sysargs[10], sysargs[11],
319 sysargs[12], sysargs[13], sysargs[14],
320 floats[0], floats[1], floats[2], floats[3], floats[4], floats[5], floats[6], floats[7],
321 arm64_r8,
322 }
323 runtime_cgocall(syscall15XABI0, unsafe.Pointer(syscall))
324 } else {
325 *syscall = syscall15Args{}
326 // This is a fallback for Windows amd64, 386, and arm. Note this may not support floats
327 syscall.a1, syscall.a2, _ = syscall_syscall15X(cfn, sysargs[0], sysargs[1], sysargs[2], sysargs[3], sysargs[4],
328 sysargs[5], sysargs[6], sysargs[7], sysargs[8], sysargs[9], sysargs[10], sysargs[11],
329 sysargs[12], sysargs[13], sysargs[14])
330 syscall.f1 = syscall.a2 // on amd64 a2 stores the float return. On 32bit platforms floats aren't support
331 }
332 if ty.NumOut() == 0 {
333 return nil
334 }
335 outType := ty.Out(0)
336 v := reflect.New(outType).Elem()
337 switch outType.Kind() {
338 case reflect.Uintptr, reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
339 v.SetUint(uint64(syscall.a1))
340 case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
341 v.SetInt(int64(syscall.a1))
342 case reflect.Bool:
343 v.SetBool(byte(syscall.a1) != 0)
344 case reflect.UnsafePointer:
345 // We take the address and then dereference it to trick go vet from creating a possible miss-use of unsafe.Pointer
346 v.SetPointer(*(*unsafe.Pointer)(unsafe.Pointer(&syscall.a1)))
347 case reflect.Ptr:
348 v = reflect.NewAt(outType, unsafe.Pointer(&syscall.a1)).Elem()
349 case reflect.Func:
350 // wrap this C function in a nicely typed Go function
351 v = reflect.New(outType)
352 RegisterFunc(v.Interface(), syscall.a1)
353 case reflect.String:
354 v.SetString(strings.GoString(syscall.a1))
355 case reflect.Float32:
356 // NOTE: syscall.r2 is only the floating return value on 64bit platforms.
357 // On 32bit platforms syscall.r2 is the upper part of a 64bit return.
358 v.SetFloat(float64(math.Float32frombits(uint32(syscall.f1))))
359 case reflect.Float64:
360 // NOTE: syscall.r2 is only the floating return value on 64bit platforms.
361 // On 32bit platforms syscall.r2 is the upper part of a 64bit return.
362 v.SetFloat(math.Float64frombits(uint64(syscall.f1)))
363 case reflect.Struct:
364 v = getStruct(outType, *syscall)
365 default:
366 panic("purego: unsupported return kind: " + outType.Kind().String())
367 }
368 if len(args) > 0 {
369 // reuse args slice instead of allocating one when possible
370 args[0] = v
371 return args[:1]
372 } else {
373 return []reflect.Value{v}
374 }
375 })
376 fn.Set(v)
377}
378
379func 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 {
380 switch v.Kind() {
381 case reflect.String:
382 ptr := strings.CString(v.String())
383 keepAlive = append(keepAlive, ptr)
384 addInt(uintptr(unsafe.Pointer(ptr)))
385 case reflect.Uintptr, reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
386 addInt(uintptr(v.Uint()))
387 case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
388 addInt(uintptr(v.Int()))
389 case reflect.Ptr, reflect.UnsafePointer, reflect.Slice:
390 // There is no need to keepAlive this pointer separately because it is kept alive in the args variable
391 addInt(v.Pointer())
392 case reflect.Func:
393 addInt(NewCallback(v.Interface()))
394 case reflect.Bool:
395 if v.Bool() {
396 addInt(1)
397 } else {
398 addInt(0)
399 }
400 case reflect.Float32:
401 addFloat(uintptr(math.Float32bits(float32(v.Float()))))
402 case reflect.Float64:
403 addFloat(uintptr(math.Float64bits(v.Float())))
404 case reflect.Struct:
405 keepAlive = addStruct(v, numInts, numFloats, numStack, addInt, addFloat, addStack, keepAlive)
406 default:
407 panic("purego: unsupported kind: " + v.Kind().String())
408 }
409 return keepAlive
410}
411
412// maxRegAllocStructSize is the biggest a struct can be while still fitting in registers.
413// if it is bigger than this than enough space must be allocated on the heap and then passed into
414// the function as the first parameter on amd64 or in R8 on arm64.
415//
416// If you change this make sure to update it in objc_runtime_darwin.go
417const maxRegAllocStructSize = 16
418
419func isAllSameFloat(ty reflect.Type) (allFloats bool, numFields int) {
420 allFloats = true
421 root := ty.Field(0).Type
422 for root.Kind() == reflect.Struct {
423 root = root.Field(0).Type
424 }
425 first := root.Kind()
426 if first != reflect.Float32 && first != reflect.Float64 {
427 allFloats = false
428 }
429 for i := 0; i < ty.NumField(); i++ {
430 f := ty.Field(i).Type
431 if f.Kind() == reflect.Struct {
432 var structNumFields int
433 allFloats, structNumFields = isAllSameFloat(f)
434 numFields += structNumFields
435 continue
436 }
437 numFields++
438 if f.Kind() != first {
439 allFloats = false
440 }
441 }
442 return allFloats, numFields
443}
444
445func checkStructFieldsSupported(ty reflect.Type) {
446 for i := 0; i < ty.NumField(); i++ {
447 f := ty.Field(i).Type
448 if f.Kind() == reflect.Array {
449 f = f.Elem()
450 } else if f.Kind() == reflect.Struct {
451 checkStructFieldsSupported(f)
452 continue
453 }
454 switch f.Kind() {
455 case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64,
456 reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64,
457 reflect.Uintptr, reflect.Ptr, reflect.UnsafePointer, reflect.Float64, reflect.Float32:
458 default:
459 panic(fmt.Sprintf("purego: struct field type %s is not supported", f))
460 }
461 }
462}
463
464func roundUpTo8(val uintptr) uintptr {
465 return (val + 7) &^ 7
466}
467
468func numOfIntegerRegisters() int {
469 switch runtime.GOARCH {
470 case "arm64":
471 return 8
472 case "amd64":
473 return 6
474 default:
475 // since this platform isn't supported and can therefore only access
476 // integer registers it is fine to return the maxArgs
477 return maxArgs
478 }
479}