golang cgocall 代码
文件路径：/src/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.
/
/ 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 (
"internal/goarch"
"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
}
var ncgocall uint64 / number of cgo calls in total for dead m
/ 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. fn must point to an ABIInternal Go entry-point.
/
/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()
checkm := gp.m
/ 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) / will call unlockOSThread
/ 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.
gp.m.incgo = true
if gp.m != checkm {
throw("m changed unexpectedly in cgocallbackg")
}
osPreemptExtEnter(gp.m)
/ going back to cgo call
reentersyscall(savedpc, uintptr(savedsp))
gp.m.syscall = syscall
}
func cgocallbackg1(fn, frame unsafe.Pointer, ctxt uintptr) {
gp := getg()
/ When we return, undo the call to lockOSThread in cgocallbackg.
/ We must still stay on the same m.
defer unlockOSThread()
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
}
/ Check whether the profiler needs to be turned on or off; this route to
/ run Go code does not use runtime.execute, so bypasses the check there.
hz := sched.profilehz
if gp.m.profilehz != hz {
setThreadCPUProfiler(hz)
}
/ 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
sched.sp = *(*uintptr)(unsafe.Pointer(sched.sp + alignUp(sys.MinFrameSize, sys.StackAlign)))
/ 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)
}
}
/ 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 any, arg any) {
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, goarch.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 += goarch.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 any) {
if debug.cgocheck == 0 {
return
}
ep := efaceOf(&val)
t := ep._type
cgoCheckArg(t, ep.data, t.kind&kindDirectIface == 0, false, cgoResultFail)
}