* builtins.def (BUILT_IN_SETJMP): Revert latest change.

[official-gcc.git] / libgo / go / runtime / cgocall.go

// 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"
)

// 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{}, args ...interface{}) {
        if debug.cgocheck == 0 {
                return
        }

        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
                }
                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
                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.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, false)
                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
        }

        roots := gcRoots
        for roots != nil {
                for j := 0; j < roots.count; j++ {
                        pr := roots.roots[j]
                        addr := uintptr(pr.decl)
                        if cgoInRange(p, addr, addr+pr.size) {
                                cgoCheckBits(pr.decl, pr.gcdata, 0, pr.ptrdata)
                                return
                        }
                }
                roots = roots.next
        }

        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
        }

        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 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)
}