| // 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. |
| |
| package runtime |
| |
| import ( |
| "runtime/internal/sys" |
| "unsafe" |
| ) |
| |
| // Functions called by cgo-generated code. |
| //go:linkname cgoCheckPointer |
| //go:linkname cgoCheckResult |
| |
| // 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, false) |
| 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 |
| } |
| |
| lo := 0 |
| hi := len(gcRootsIndex) |
| for lo < hi { |
| m := lo + (hi-lo)/2 |
| pr := gcRootsIndex[m] |
| addr := uintptr(pr.decl) |
| if cgoInRange(p, addr, addr+pr.size) { |
| cgoCheckBits(pr.decl, pr.gcdata, 0, pr.ptrdata) |
| return |
| } |
| if uintptr(p) < addr { |
| hi = m |
| } else { |
| lo = m + 1 |
| } |
| } |
| |
| 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 |
| } |
| |
| roots := gcRoots |
| for roots != nil { |
| for i := 0; i < roots.count; i++ { |
| pr := roots.roots[i] |
| addr := uintptr(pr.decl) |
| if cgoInRange(p, addr, addr+pr.size) { |
| return true |
| } |
| } |
| roots = roots.next |
| } |
| |
| 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) |
| } |