| // Copyright 2009 The Go Authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style |
| // license that can be found in the LICENSE file. |
| |
| // Cgo call and callback support. |
| // |
| // To call into the C function f from Go, the cgo-generated code calls |
| // runtime.cgocall(_cgo_Cfunc_f, frame), where _cgo_Cfunc_f is a |
| // gcc-compiled function written by cgo. |
| // |
| // runtime.cgocall (below) locks g to m, calls entersyscall |
| // so as not to block other goroutines or the garbage collector, |
| // and then calls runtime.asmcgocall(_cgo_Cfunc_f, frame). |
| // |
| // runtime.asmcgocall (in asm_$GOARCH.s) switches to the m->g0 stack |
| // (assumed to be an operating system-allocated stack, so safe to run |
| // gcc-compiled code on) and calls _cgo_Cfunc_f(frame). |
| // |
| // _cgo_Cfunc_f invokes the actual C function f with arguments |
| // taken from the frame structure, records the results in the frame, |
| // and returns to runtime.asmcgocall. |
| // |
| // After it regains control, runtime.asmcgocall switches back to the |
| // original g (m->curg)'s stack and returns to runtime.cgocall. |
| // |
| // After it regains control, runtime.cgocall calls exitsyscall, which blocks |
| // until this m can run Go code without violating the $GOMAXPROCS limit, |
| // and then unlocks g from m. |
| // |
| // The above description skipped over the possibility of the gcc-compiled |
| // function f calling back into Go. If that happens, we continue down |
| // the rabbit hole during the execution of f. |
| // |
| // To make it possible for gcc-compiled C code to call a Go function p.GoF, |
| // cgo writes a gcc-compiled function named GoF (not p.GoF, since gcc doesn't |
| // know about packages). The gcc-compiled C function f calls GoF. |
| // |
| // GoF calls crosscall2(_cgoexp_GoF, frame, framesize). Crosscall2 |
| // (in cgo/gcc_$GOARCH.S, a gcc-compiled assembly file) is a two-argument |
| // adapter from the gcc function call ABI to the 6c function call ABI. |
| // It is called from gcc to call 6c functions. In this case it calls |
| // _cgoexp_GoF(frame, framesize), still running on m->g0's stack |
| // and outside the $GOMAXPROCS limit. Thus, this code cannot yet |
| // call arbitrary Go code directly and must be careful not to allocate |
| // memory or use up m->g0's stack. |
| // |
| // _cgoexp_GoF calls runtime.cgocallback(p.GoF, frame, framesize, ctxt). |
| // (The reason for having _cgoexp_GoF instead of writing a crosscall3 |
| // to make this call directly is that _cgoexp_GoF, because it is compiled |
| // with 6c instead of gcc, can refer to dotted names like |
| // runtime.cgocallback and p.GoF.) |
| // |
| // runtime.cgocallback (in asm_$GOARCH.s) switches from m->g0's |
| // stack to the original g (m->curg)'s stack, on which it calls |
| // runtime.cgocallbackg(p.GoF, frame, framesize). |
| // As part of the stack switch, runtime.cgocallback saves the current |
| // SP as m->g0->sched.sp, so that any use of m->g0's stack during the |
| // execution of the callback will be done below the existing stack frames. |
| // Before overwriting m->g0->sched.sp, it pushes the old value on the |
| // m->g0 stack, so that it can be restored later. |
| // |
| // runtime.cgocallbackg (below) is now running on a real goroutine |
| // stack (not an m->g0 stack). First it calls runtime.exitsyscall, which will |
| // block until the $GOMAXPROCS limit allows running this goroutine. |
| // Once exitsyscall has returned, it is safe to do things like call the memory |
| // allocator or invoke the Go callback function p.GoF. runtime.cgocallbackg |
| // first defers a function to unwind m->g0.sched.sp, so that if p.GoF |
| // panics, m->g0.sched.sp will be restored to its old value: the m->g0 stack |
| // and the m->curg stack will be unwound in lock step. |
| // Then it calls p.GoF. Finally it pops but does not execute the deferred |
| // function, calls runtime.entersyscall, and returns to runtime.cgocallback. |
| // |
| // After it regains control, runtime.cgocallback switches back to |
| // m->g0's stack (the pointer is still in m->g0.sched.sp), restores the old |
| // m->g0.sched.sp value from the stack, and returns to _cgoexp_GoF. |
| // |
| // _cgoexp_GoF immediately returns to crosscall2, which restores the |
| // callee-save registers for gcc and returns to GoF, which returns to f. |
| |
| package runtime |
| |
| import ( |
| "runtime/internal/atomic" |
| "runtime/internal/sys" |
| "unsafe" |
| ) |
| |
| // Addresses collected in a cgo backtrace when crashing. |
| // Length must match arg.Max in x_cgo_callers in runtime/cgo/gcc_traceback.c. |
| type cgoCallers [32]uintptr |
| |
| // Call from Go to C. |
| //go:nosplit |
| func cgocall(fn, arg unsafe.Pointer) int32 { |
| if !iscgo && GOOS != "solaris" && GOOS != "windows" { |
| throw("cgocall unavailable") |
| } |
| |
| if fn == nil { |
| throw("cgocall nil") |
| } |
| |
| if raceenabled { |
| racereleasemerge(unsafe.Pointer(&racecgosync)) |
| } |
| |
| /* |
| * Lock g to m to ensure we stay on the same stack if we do a |
| * cgo callback. Add entry to defer stack in case of panic. |
| */ |
| lockOSThread() |
| mp := getg().m |
| mp.ncgocall++ |
| mp.ncgo++ |
| defer endcgo(mp) |
| |
| // Reset traceback. |
| mp.cgoCallers[0] = 0 |
| |
| /* |
| * Announce we are entering a system call |
| * so that the scheduler knows to create another |
| * M to run goroutines while we are in the |
| * foreign code. |
| * |
| * The call to asmcgocall is guaranteed not to |
| * split the stack and does not allocate memory, |
| * so it is safe to call while "in a system call", outside |
| * the $GOMAXPROCS accounting. |
| */ |
| entersyscall(0) |
| errno := asmcgocall(fn, arg) |
| exitsyscall(0) |
| |
| return errno |
| } |
| |
| //go:nosplit |
| func endcgo(mp *m) { |
| mp.ncgo-- |
| |
| if raceenabled { |
| raceacquire(unsafe.Pointer(&racecgosync)) |
| } |
| |
| unlockOSThread() // invalidates mp |
| } |
| |
| // Call from C back to Go. |
| //go:nosplit |
| func cgocallbackg(ctxt uintptr) { |
| gp := getg() |
| if gp != gp.m.curg { |
| println("runtime: bad g in cgocallback") |
| exit(2) |
| } |
| |
| // Save current syscall parameters, so m.syscall can be |
| // used again if callback decide to make syscall. |
| syscall := gp.m.syscall |
| |
| // entersyscall saves the caller's SP to allow the GC to trace the Go |
| // stack. However, since we're returning to an earlier stack frame and |
| // need to pair with the entersyscall() call made by cgocall, we must |
| // save syscall* and let reentersyscall restore them. |
| savedsp := unsafe.Pointer(gp.syscallsp) |
| savedpc := gp.syscallpc |
| exitsyscall(0) // coming out of cgo call |
| |
| cgocallbackg1(ctxt) |
| |
| // going back to cgo call |
| reentersyscall(savedpc, uintptr(savedsp)) |
| |
| gp.m.syscall = syscall |
| } |
| |
| func cgocallbackg1(ctxt uintptr) { |
| gp := getg() |
| if gp.m.needextram || atomic.Load(&extraMWaiters) > 0 { |
| gp.m.needextram = false |
| systemstack(newextram) |
| } |
| |
| if ctxt != 0 { |
| s := append(gp.cgoCtxt, ctxt) |
| |
| // Now we need to set gp.cgoCtxt = s, but we could get |
| // a SIGPROF signal while manipulating the slice, and |
| // the SIGPROF handler could pick up gp.cgoCtxt while |
| // tracing up the stack. We need to ensure that the |
| // handler always sees a valid slice, so set the |
| // values in an order such that it always does. |
| p := (*slice)(unsafe.Pointer(&gp.cgoCtxt)) |
| atomicstorep(unsafe.Pointer(&p.array), unsafe.Pointer(&s[0])) |
| p.cap = cap(s) |
| p.len = len(s) |
| |
| defer func(gp *g) { |
| // Decrease the length of the slice by one, safely. |
| p := (*slice)(unsafe.Pointer(&gp.cgoCtxt)) |
| p.len-- |
| }(gp) |
| } |
| |
| if gp.m.ncgo == 0 { |
| // The C call to Go came from a thread not currently running |
| // any Go. In the case of -buildmode=c-archive or c-shared, |
| // this call may be coming in before package initialization |
| // is complete. Wait until it is. |
| <-main_init_done |
| } |
| |
| // Add entry to defer stack in case of panic. |
| restore := true |
| defer unwindm(&restore) |
| |
| if raceenabled { |
| raceacquire(unsafe.Pointer(&racecgosync)) |
| } |
| |
| type args struct { |
| fn *funcval |
| arg unsafe.Pointer |
| argsize uintptr |
| } |
| var cb *args |
| |
| // Location of callback arguments depends on stack frame layout |
| // and size of stack frame of cgocallback_gofunc. |
| sp := gp.m.g0.sched.sp |
| switch GOARCH { |
| default: |
| throw("cgocallbackg is unimplemented on arch") |
| case "arm": |
| // On arm, stack frame is two words and there's a saved LR between |
| // SP and the stack frame and between the stack frame and the arguments. |
| cb = (*args)(unsafe.Pointer(sp + 4*sys.PtrSize)) |
| case "arm64": |
| // On arm64, stack frame is four words and there's a saved LR between |
| // SP and the stack frame and between the stack frame and the arguments. |
| cb = (*args)(unsafe.Pointer(sp + 5*sys.PtrSize)) |
| case "amd64": |
| // On amd64, stack frame is two words, plus caller PC. |
| if framepointer_enabled { |
| // In this case, there's also saved BP. |
| cb = (*args)(unsafe.Pointer(sp + 4*sys.PtrSize)) |
| break |
| } |
| cb = (*args)(unsafe.Pointer(sp + 3*sys.PtrSize)) |
| case "386": |
| // On 386, stack frame is three words, plus caller PC. |
| cb = (*args)(unsafe.Pointer(sp + 4*sys.PtrSize)) |
| case "ppc64", "ppc64le", "s390x": |
| // On ppc64 and s390x, the callback arguments are in the arguments area of |
| // cgocallback's stack frame. The stack looks like this: |
| // +--------------------+------------------------------+ |
| // | | ... | |
| // | cgoexp_$fn +------------------------------+ |
| // | | fixed frame area | |
| // +--------------------+------------------------------+ |
| // | | arguments area | |
| // | cgocallback +------------------------------+ <- sp + 2*minFrameSize + 2*ptrSize |
| // | | fixed frame area | |
| // +--------------------+------------------------------+ <- sp + minFrameSize + 2*ptrSize |
| // | | local variables (2 pointers) | |
| // | cgocallback_gofunc +------------------------------+ <- sp + minFrameSize |
| // | | fixed frame area | |
| // +--------------------+------------------------------+ <- sp |
| cb = (*args)(unsafe.Pointer(sp + 2*sys.MinFrameSize + 2*sys.PtrSize)) |
| case "mips64", "mips64le": |
| // On mips64x, stack frame is two words and there's a saved LR between |
| // SP and the stack frame and between the stack frame and the arguments. |
| cb = (*args)(unsafe.Pointer(sp + 4*sys.PtrSize)) |
| } |
| |
| // Invoke callback. |
| // NOTE(rsc): passing nil for argtype means that the copying of the |
| // results back into cb.arg happens without any corresponding write barriers. |
| // For cgo, cb.arg points into a C stack frame and therefore doesn't |
| // hold any pointers that the GC can find anyway - the write barrier |
| // would be a no-op. |
| reflectcall(nil, unsafe.Pointer(cb.fn), cb.arg, uint32(cb.argsize), 0) |
| |
| if raceenabled { |
| racereleasemerge(unsafe.Pointer(&racecgosync)) |
| } |
| if msanenabled { |
| // Tell msan that we wrote to the entire argument block. |
| // This tells msan that we set the results. |
| // Since we have already called the function it doesn't |
| // matter that we are writing to the non-result parameters. |
| msanwrite(cb.arg, cb.argsize) |
| } |
| |
| // Do not unwind m->g0->sched.sp. |
| // Our caller, cgocallback, will do that. |
| restore = false |
| } |
| |
| func unwindm(restore *bool) { |
| if !*restore { |
| return |
| } |
| // Restore sp saved by cgocallback during |
| // unwind of g's stack (see comment at top of file). |
| mp := acquirem() |
| sched := &mp.g0.sched |
| switch GOARCH { |
| default: |
| throw("unwindm not implemented") |
| case "386", "amd64", "arm", "ppc64", "ppc64le", "mips64", "mips64le", "s390x": |
| sched.sp = *(*uintptr)(unsafe.Pointer(sched.sp + sys.MinFrameSize)) |
| case "arm64": |
| sched.sp = *(*uintptr)(unsafe.Pointer(sched.sp + 16)) |
| } |
| releasem(mp) |
| } |
| |
| // called from assembly |
| func badcgocallback() { |
| throw("misaligned stack in cgocallback") |
| } |
| |
| // called from (incomplete) assembly |
| func cgounimpl() { |
| throw("cgo not implemented") |
| } |
| |
| var racecgosync uint64 // represents possible synchronization in C code |
| |
| // Pointer checking for cgo code. |
| |
| // We want to detect all cases where a program that does not use |
| // unsafe makes a cgo call passing a Go pointer to memory that |
| // contains a Go pointer. Here a Go pointer is defined as a pointer |
| // to memory allocated by the Go runtime. Programs that use unsafe |
| // can evade this restriction easily, so we don't try to catch them. |
| // The cgo program will rewrite all possibly bad pointer arguments to |
| // call cgoCheckPointer, where we can catch cases of a Go pointer |
| // pointing to a Go pointer. |
| |
| // Complicating matters, taking the address of a slice or array |
| // element permits the C program to access all elements of the slice |
| // or array. In that case we will see a pointer to a single element, |
| // but we need to check the entire data structure. |
| |
| // The cgoCheckPointer call takes additional arguments indicating that |
| // it was called on an address expression. An additional argument of |
| // true means that it only needs to check a single element. An |
| // additional argument of a slice or array means that it needs to |
| // check the entire slice/array, but nothing else. Otherwise, the |
| // pointer could be anything, and we check the entire heap object, |
| // which is conservative but safe. |
| |
| // When and if we implement a moving garbage collector, |
| // cgoCheckPointer will pin the pointer for the duration of the cgo |
| // call. (This is necessary but not sufficient; the cgo program will |
| // also have to change to pin Go pointers that cannot point to Go |
| // pointers.) |
| |
| // cgoCheckPointer checks if the argument contains a Go pointer that |
| // points to a Go pointer, and panics if it does. It returns the pointer. |
| func cgoCheckPointer(ptr interface{}, args ...interface{}) interface{} { |
| if debug.cgocheck == 0 { |
| return ptr |
| } |
| |
| ep := (*eface)(unsafe.Pointer(&ptr)) |
| t := ep._type |
| |
| top := true |
| if len(args) > 0 && (t.kind&kindMask == kindPtr || t.kind&kindMask == kindUnsafePointer) { |
| p := ep.data |
| if t.kind&kindDirectIface == 0 { |
| p = *(*unsafe.Pointer)(p) |
| } |
| if !cgoIsGoPointer(p) { |
| return ptr |
| } |
| aep := (*eface)(unsafe.Pointer(&args[0])) |
| switch aep._type.kind & kindMask { |
| case kindBool: |
| if t.kind&kindMask == kindUnsafePointer { |
| // We don't know the type of the element. |
| break |
| } |
| pt := (*ptrtype)(unsafe.Pointer(t)) |
| cgoCheckArg(pt.elem, p, true, false, cgoCheckPointerFail) |
| return ptr |
| case kindSlice: |
| // Check the slice rather than the pointer. |
| ep = aep |
| t = ep._type |
| case kindArray: |
| // Check the array rather than the pointer. |
| // Pass top as false since we have a pointer |
| // to the array. |
| ep = aep |
| t = ep._type |
| top = false |
| default: |
| throw("can't happen") |
| } |
| } |
| |
| cgoCheckArg(t, ep.data, t.kind&kindDirectIface == 0, top, cgoCheckPointerFail) |
| return ptr |
| } |
| |
| const cgoCheckPointerFail = "cgo argument has Go pointer to Go pointer" |
| const cgoResultFail = "cgo result has Go pointer" |
| |
| // cgoCheckArg is the real work of cgoCheckPointer. The argument p |
| // is either a pointer to the value (of type t), or the value itself, |
| // depending on indir. The top parameter is whether we are at the top |
| // level, where Go pointers are allowed. |
| func cgoCheckArg(t *_type, p unsafe.Pointer, indir, top bool, msg string) { |
| if t.kind&kindNoPointers != 0 { |
| // If the type has no pointers there is nothing to do. |
| return |
| } |
| |
| switch t.kind & kindMask { |
| default: |
| throw("can't happen") |
| case kindArray: |
| at := (*arraytype)(unsafe.Pointer(t)) |
| if !indir { |
| if at.len != 1 { |
| throw("can't happen") |
| } |
| cgoCheckArg(at.elem, p, at.elem.kind&kindDirectIface == 0, top, msg) |
| return |
| } |
| for i := uintptr(0); i < at.len; i++ { |
| cgoCheckArg(at.elem, p, true, top, msg) |
| p = add(p, at.elem.size) |
| } |
| case kindChan, kindMap: |
| // These types contain internal pointers that will |
| // always be allocated in the Go heap. It's never OK |
| // to pass them to C. |
| panic(errorString(msg)) |
| case kindFunc: |
| if indir { |
| p = *(*unsafe.Pointer)(p) |
| } |
| if !cgoIsGoPointer(p) { |
| return |
| } |
| panic(errorString(msg)) |
| case kindInterface: |
| it := *(**_type)(p) |
| if it == nil { |
| return |
| } |
| // A type known at compile time is OK since it's |
| // constant. A type not known at compile time will be |
| // in the heap and will not be OK. |
| if inheap(uintptr(unsafe.Pointer(it))) { |
| panic(errorString(msg)) |
| } |
| p = *(*unsafe.Pointer)(add(p, sys.PtrSize)) |
| if !cgoIsGoPointer(p) { |
| return |
| } |
| if !top { |
| panic(errorString(msg)) |
| } |
| cgoCheckArg(it, p, it.kind&kindDirectIface == 0, false, msg) |
| case kindSlice: |
| st := (*slicetype)(unsafe.Pointer(t)) |
| s := (*slice)(p) |
| p = s.array |
| if !cgoIsGoPointer(p) { |
| return |
| } |
| if !top { |
| panic(errorString(msg)) |
| } |
| if st.elem.kind&kindNoPointers != 0 { |
| return |
| } |
| for i := 0; i < s.cap; i++ { |
| cgoCheckArg(st.elem, p, true, false, msg) |
| p = add(p, st.elem.size) |
| } |
| case kindString: |
| ss := (*stringStruct)(p) |
| if !cgoIsGoPointer(ss.str) { |
| return |
| } |
| if !top { |
| panic(errorString(msg)) |
| } |
| case kindStruct: |
| st := (*structtype)(unsafe.Pointer(t)) |
| if !indir { |
| if len(st.fields) != 1 { |
| throw("can't happen") |
| } |
| cgoCheckArg(st.fields[0].typ, p, st.fields[0].typ.kind&kindDirectIface == 0, top, msg) |
| return |
| } |
| for _, f := range st.fields { |
| cgoCheckArg(f.typ, add(p, f.offset), true, top, msg) |
| } |
| case kindPtr, kindUnsafePointer: |
| if indir { |
| p = *(*unsafe.Pointer)(p) |
| } |
| |
| if !cgoIsGoPointer(p) { |
| return |
| } |
| if !top { |
| panic(errorString(msg)) |
| } |
| |
| cgoCheckUnknownPointer(p, msg) |
| } |
| } |
| |
| // cgoCheckUnknownPointer is called for an arbitrary pointer into Go |
| // memory. It checks whether that Go memory contains any other |
| // pointer into Go memory. If it does, we panic. |
| // The return values are unused but useful to see in panic tracebacks. |
| func cgoCheckUnknownPointer(p unsafe.Pointer, msg string) (base, i uintptr) { |
| if cgoInRange(p, mheap_.arena_start, mheap_.arena_used) { |
| if !inheap(uintptr(p)) { |
| // On 32-bit systems it is possible for C's allocated memory |
| // to have addresses between arena_start and arena_used. |
| // Either this pointer is a stack or an unused span or it's |
| // a C allocation. Escape analysis should prevent the first, |
| // garbage collection should prevent the second, |
| // and the third is completely OK. |
| return |
| } |
| |
| b, hbits, span, _ := heapBitsForObject(uintptr(p), 0, 0) |
| base = b |
| if base == 0 { |
| return |
| } |
| n := span.elemsize |
| for i = uintptr(0); i < n; i += sys.PtrSize { |
| if i != 1*sys.PtrSize && !hbits.morePointers() { |
| // No more possible pointers. |
| break |
| } |
| if hbits.isPointer() { |
| if cgoIsGoPointer(*(*unsafe.Pointer)(unsafe.Pointer(base + i))) { |
| panic(errorString(msg)) |
| } |
| } |
| hbits = hbits.next() |
| } |
| |
| return |
| } |
| |
| for datap := &firstmoduledata; datap != nil; datap = datap.next { |
| if cgoInRange(p, datap.data, datap.edata) || cgoInRange(p, datap.bss, datap.ebss) { |
| // We have no way to know the size of the object. |
| // We have to assume that it might contain a pointer. |
| panic(errorString(msg)) |
| } |
| // In the text or noptr sections, we know that the |
| // pointer does not point to a Go pointer. |
| } |
| |
| return |
| } |
| |
| // cgoIsGoPointer returns whether the pointer is a Go pointer--a |
| // pointer to Go memory. We only care about Go memory that might |
| // contain pointers. |
| //go:nosplit |
| //go:nowritebarrierrec |
| func cgoIsGoPointer(p unsafe.Pointer) bool { |
| if p == nil { |
| return false |
| } |
| |
| if inHeapOrStack(uintptr(p)) { |
| return true |
| } |
| |
| for datap := &firstmoduledata; datap != nil; datap = datap.next { |
| if cgoInRange(p, datap.data, datap.edata) || cgoInRange(p, datap.bss, datap.ebss) { |
| return true |
| } |
| } |
| |
| return false |
| } |
| |
| // cgoInRange returns whether p is between start and end. |
| //go:nosplit |
| //go:nowritebarrierrec |
| func cgoInRange(p unsafe.Pointer, start, end uintptr) bool { |
| return start <= uintptr(p) && uintptr(p) < end |
| } |
| |
| // cgoCheckResult is called to check the result parameter of an |
| // exported Go function. It panics if the result is or contains a Go |
| // pointer. |
| func cgoCheckResult(val interface{}) { |
| if debug.cgocheck == 0 { |
| return |
| } |
| |
| ep := (*eface)(unsafe.Pointer(&val)) |
| t := ep._type |
| cgoCheckArg(t, ep.data, t.kind&kindDirectIface == 0, false, cgoResultFail) |
| } |