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authorDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-28 13:14:23 +0000
committerDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-28 13:14:23 +0000
commit73df946d56c74384511a194dd01dbe099584fd1a (patch)
treefd0bcea490dd81327ddfbb31e215439672c9a068 /src/runtime/cgocall.go
parentInitial commit. (diff)
downloadgolang-1.16-73df946d56c74384511a194dd01dbe099584fd1a.tar.xz
golang-1.16-73df946d56c74384511a194dd01dbe099584fd1a.zip
Adding upstream version 1.16.10.upstream/1.16.10upstream
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'src/runtime/cgocall.go')
-rw-r--r--src/runtime/cgocall.go628
1 files changed, 628 insertions, 0 deletions
diff --git a/src/runtime/cgocall.go b/src/runtime/cgocall.go
new file mode 100644
index 0000000..20cacd6
--- /dev/null
+++ b/src/runtime/cgocall.go
@@ -0,0 +1,628 @@
+// 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", "riscv64":
+ 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)
+}