| // 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) 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 $GOMAXPROCS limit, |
| // and then unlocks g from m. |
| // |
| // The above description skipped over the possibility of the gcc-compiled |
| // function f calling back into Go. If that happens, we continue down |
| // the rabbit hole during the execution of f. |
| // |
| // To make it possible for gcc-compiled C code to call a Go function p.GoF, |
| // cgo writes a gcc-compiled function named GoF (not p.GoF, since gcc doesn't |
| // know about packages). The gcc-compiled C function f calls GoF. |
| // |
| // GoF initializes "frame", a structure containing all of its |
| // arguments and slots for p.GoF's results. It calls |
| // crosscall2(_cgoexp_GoF, frame, framesize, ctxt) using the gcc ABI. |
| // |
| // crosscall2 (in cgo/asm_$GOARCH.s) is a four-argument adapter from |
| // the gcc function call ABI to the gc function call ABI. At this |
| // point we're in the Go runtime, but we're still running on m.g0's |
| // stack and outside the $GOMAXPROCS limit. crosscall2 calls |
| // runtime.cgocallback(_cgoexp_GoF, frame, ctxt) using the gc ABI. |
| // (crosscall2's framesize argument is no longer used, but there's one |
| // case where SWIG calls crosscall2 directly and expects to pass this |
| // argument. See _cgo_panic.) |
| // |
| // runtime.cgocallback (in asm_$GOARCH.s) switches from m.g0's stack |
| // to the original g (m.curg)'s stack, on which it calls |
| // runtime.cgocallbackg(_cgoexp_GoF, frame, ctxt). 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. 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 _cgoexp_GoF(frame). |
| // |
| // _cgoexp_GoF, which was generated by cmd/cgo, unpacks the arguments |
| // from frame, calls p.GoF, writes the results back to frame, and |
| // returns. Now we start unwinding this whole process. |
| // |
| // runtime.cgocallbackg pops but does not execute the deferred |
| // function to unwind m.g0.sched.sp, 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 crosscall2. |
| // |
| // crosscall2 restores the callee-save registers for gcc and returns |
| // to GoF, which unpacks any result values and 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 |
| |
| // argset matches runtime/cgo/linux_syscall.c:argset_t |
| type argset struct { |
| args unsafe.Pointer |
| retval uintptr |
| } |
| |
| // wrapper for syscall package to call cgocall for libc (cgo) calls. |
| //go:linkname syscall_cgocaller syscall.cgocaller |
| //go:nosplit |
| //go:uintptrescapes |
| func syscall_cgocaller(fn unsafe.Pointer, args ...uintptr) uintptr { |
| as := argset{args: unsafe.Pointer(&args[0])} |
| cgocall(fn, unsafe.Pointer(&as)) |
| return as.retval |
| } |
| |
| // Call from Go to C. |
| // |
| // This must be nosplit because it's used for syscalls on some |
| // platforms. Syscalls may have untyped arguments on the stack, so |
| // it's not safe to grow or scan the stack. |
| // |
| //go:nosplit |
| func cgocall(fn, arg unsafe.Pointer) int32 { |
| if !iscgo && GOOS != "solaris" && GOOS != "illumos" && GOOS != "windows" { |
| throw("cgocall unavailable") |
| } |
| |
| if fn == nil { |
| throw("cgocall nil") |
| } |
| |
| if raceenabled { |
| racereleasemerge(unsafe.Pointer(&racecgosync)) |
| } |
| |
| mp := getg().m |
| mp.ncgocall++ |
| mp.ncgo++ |
| |
| // 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 |
| // grow the stack and does not allocate memory, |
| // so it is safe to call while "in a system call", outside |
| // the $GOMAXPROCS accounting. |
| // |
| // fn may call back into Go code, in which case we'll exit the |
| // "system call", run the Go code (which may grow the stack), |
| // and then re-enter the "system call" reusing the PC and SP |
| // saved by entersyscall here. |
| entersyscall() |
| |
| // Tell asynchronous preemption that we're entering external |
| // code. We do this after entersyscall because this may block |
| // and cause an async preemption to fail, but at this point a |
| // sync preemption will succeed (though this is not a matter |
| // of correctness). |
| osPreemptExtEnter(mp) |
| |
| mp.incgo = true |
| errno := asmcgocall(fn, arg) |
| |
| // Update accounting before exitsyscall because exitsyscall may |
| // reschedule us on to a different M. |
| mp.incgo = false |
| mp.ncgo-- |
| |
| osPreemptExtExit(mp) |
| |
| exitsyscall() |
| |
| // Note that raceacquire must be called only after exitsyscall has |
| // wired this M to a P. |
| if raceenabled { |
| raceacquire(unsafe.Pointer(&racecgosync)) |
| } |
| |
| // From the garbage collector's perspective, time can move |
| // backwards in the sequence above. If there's a callback into |
| // Go code, GC will see this function at the call to |
| // asmcgocall. When the Go call later returns to C, the |
| // syscall PC/SP is rolled back and the GC sees this function |
| // back at the call to entersyscall. Normally, fn and arg |
| // would be live at entersyscall and dead at asmcgocall, so if |
| // time moved backwards, GC would see these arguments as dead |
| // and then live. Prevent these undead arguments from crashing |
| // GC by forcing them to stay live across this time warp. |
| KeepAlive(fn) |
| KeepAlive(arg) |
| KeepAlive(mp) |
| |
| return errno |
| } |
| |
| // Call from C back to Go. |
| //go:nosplit |
| func cgocallbackg(fn, frame unsafe.Pointer, ctxt uintptr) { |
| gp := getg() |
| if gp != gp.m.curg { |
| println("runtime: bad g in cgocallback") |
| exit(2) |
| } |
| |
| // The call from C is on gp.m's g0 stack, so we must ensure |
| // that we stay on that M. We have to do this before calling |
| // exitsyscall, since it would otherwise be free to move us to |
| // a different M. The call to unlockOSThread is in unwindm. |
| lockOSThread() |
| |
| // 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() // coming out of cgo call |
| gp.m.incgo = false |
| |
| osPreemptExtExit(gp.m) |
| |
| cgocallbackg1(fn, frame, ctxt) |
| |
| // At this point unlockOSThread has been called. |
| // The following code must not change to a different m. |
| // This is enforced by checking incgo in the schedule function. |
| |
| osPreemptExtEnter(gp.m) |
| |
| gp.m.incgo = true |
| // going back to cgo call |
| reentersyscall(savedpc, uintptr(savedsp)) |
| |
| gp.m.syscall = syscall |
| } |
| |
| func cgocallbackg1(fn, frame unsafe.Pointer, 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)) |
| } |
| |
| // Invoke callback. This function is generated by cmd/cgo and |
| // will unpack the argument frame and call the Go function. |
| var cb func(frame unsafe.Pointer) |
| cbFV := funcval{uintptr(fn)} |
| *(*unsafe.Pointer)(unsafe.Pointer(&cb)) = noescape(unsafe.Pointer(&cbFV)) |
| cb(frame) |
| |
| if raceenabled { |
| racereleasemerge(unsafe.Pointer(&racecgosync)) |
| } |
| |
| // Do not unwind m->g0->sched.sp. |
| // Our caller, cgocallback, will do that. |
| restore = false |
| } |
| |
| func unwindm(restore *bool) { |
| if *restore { |
| // 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", "mips", "mipsle": |
| sched.sp = *(*uintptr)(unsafe.Pointer(sched.sp + sys.MinFrameSize)) |
| case "arm64": |
| sched.sp = *(*uintptr)(unsafe.Pointer(sched.sp + 16)) |
| } |
| |
| // Do the accounting that cgocall will not have a chance to do |
| // during an unwind. |
| // |
| // In the case where a Go call originates from C, ncgo is 0 |
| // and there is no matching cgocall to end. |
| if mp.ncgo > 0 { |
| mp.incgo = false |
| mp.ncgo-- |
| osPreemptExtExit(mp) |
| } |
| |
| releasem(mp) |
| } |
| |
| // Undo the call to lockOSThread in cgocallbackg. |
| // We must still stay on the same m. |
| unlockOSThread() |
| } |
| |
| // 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. |
| func cgoCheckPointer(ptr interface{}, arg interface{}) { |
| if debug.cgocheck == 0 { |
| return |
| } |
| |
| ep := efaceOf(&ptr) |
| t := ep._type |
| |
| top := true |
| if arg != nil && (t.kind&kindMask == kindPtr || t.kind&kindMask == kindUnsafePointer) { |
| p := ep.data |
| if t.kind&kindDirectIface == 0 { |
| p = *(*unsafe.Pointer)(p) |
| } |
| if p == nil || !cgoIsGoPointer(p) { |
| return |
| } |
| aep := efaceOf(&arg) |
| 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 |
| 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) |
| } |
| |
| 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.ptrdata == 0 || p == nil { |
| // 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 p == nil || !cgoIsGoPointer(p) { |
| return |
| } |
| if !top { |
| panic(errorString(msg)) |
| } |
| if st.elem.ptrdata == 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 { |
| if f.typ.ptrdata == 0 { |
| continue |
| } |
| cgoCheckArg(f.typ, add(p, f.offset()), true, top, msg) |
| } |
| case kindPtr, kindUnsafePointer: |
| if indir { |
| p = *(*unsafe.Pointer)(p) |
| if p == nil { |
| return |
| } |
| } |
| |
| 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 inheap(uintptr(p)) { |
| b, span, _ := findObject(uintptr(p), 0, 0) |
| base = b |
| if base == 0 { |
| return |
| } |
| hbits := heapBitsForAddr(base) |
| n := span.elemsize |
| for i = uintptr(0); i < n; i += sys.PtrSize { |
| if !hbits.morePointers() { |
| // No more possible pointers. |
| break |
| } |
| if hbits.isPointer() && cgoIsGoPointer(*(*unsafe.Pointer)(unsafe.Pointer(base + i))) { |
| panic(errorString(msg)) |
| } |
| hbits = hbits.next() |
| } |
| |
| return |
| } |
| |
| for _, datap := range activeModules() { |
| 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 reports 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 := range activeModules() { |
| if cgoInRange(p, datap.data, datap.edata) || cgoInRange(p, datap.bss, datap.ebss) { |
| return true |
| } |
| } |
| |
| return false |
| } |
| |
| // cgoInRange reports 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 := efaceOf(&val) |
| t := ep._type |
| cgoCheckArg(t, ep.data, t.kind&kindDirectIface == 0, false, cgoResultFail) |
| } |