Source file src/runtime/cgocall.go

     1  // Copyright 2009 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  // Cgo call and callback support.
     6  //
     7  // To call into the C function f from Go, the cgo-generated code calls
     8  // runtime.cgocall(_cgo_Cfunc_f, frame), where _cgo_Cfunc_f is a
     9  // gcc-compiled function written by cgo.
    10  //
    11  // runtime.cgocall (below) calls entersyscall so as not to block
    12  // other goroutines or the garbage collector, and then calls
    13  // runtime.asmcgocall(_cgo_Cfunc_f, frame).
    14  //
    15  // runtime.asmcgocall (in asm_$GOARCH.s) switches to the m->g0 stack
    16  // (assumed to be an operating system-allocated stack, so safe to run
    17  // gcc-compiled code on) and calls _cgo_Cfunc_f(frame).
    18  //
    19  // _cgo_Cfunc_f invokes the actual C function f with arguments
    20  // taken from the frame structure, records the results in the frame,
    21  // and returns to runtime.asmcgocall.
    22  //
    23  // After it regains control, runtime.asmcgocall switches back to the
    24  // original g (m->curg)'s stack and returns to runtime.cgocall.
    25  //
    26  // After it regains control, runtime.cgocall calls exitsyscall, which blocks
    27  // until this m can run Go code without violating the $GOMAXPROCS limit,
    28  // and then unlocks g from m.
    29  //
    30  // The above description skipped over the possibility of the gcc-compiled
    31  // function f calling back into Go. If that happens, we continue down
    32  // the rabbit hole during the execution of f.
    33  //
    34  // To make it possible for gcc-compiled C code to call a Go function p.GoF,
    35  // cgo writes a gcc-compiled function named GoF (not p.GoF, since gcc doesn't
    36  // know about packages).  The gcc-compiled C function f calls GoF.
    37  //
    38  // GoF initializes "frame", a structure containing all of its
    39  // arguments and slots for p.GoF's results. It calls
    40  // crosscall2(_cgoexp_GoF, frame, framesize, ctxt) using the gcc ABI.
    41  //
    42  // crosscall2 (in cgo/asm_$GOARCH.s) is a four-argument adapter from
    43  // the gcc function call ABI to the gc function call ABI. At this
    44  // point we're in the Go runtime, but we're still running on m.g0's
    45  // stack and outside the $GOMAXPROCS limit. crosscall2 calls
    46  // runtime.cgocallback(_cgoexp_GoF, frame, ctxt) using the gc ABI.
    47  // (crosscall2's framesize argument is no longer used, but there's one
    48  // case where SWIG calls crosscall2 directly and expects to pass this
    49  // argument. See _cgo_panic.)
    50  //
    51  // runtime.cgocallback (in asm_$GOARCH.s) switches from m.g0's stack
    52  // to the original g (m.curg)'s stack, on which it calls
    53  // runtime.cgocallbackg(_cgoexp_GoF, frame, ctxt). As part of the
    54  // stack switch, runtime.cgocallback saves the current SP as
    55  // m.g0.sched.sp, so that any use of m.g0's stack during the execution
    56  // of the callback will be done below the existing stack frames.
    57  // Before overwriting m.g0.sched.sp, it pushes the old value on the
    58  // m.g0 stack, so that it can be restored later.
    59  //
    60  // runtime.cgocallbackg (below) is now running on a real goroutine
    61  // stack (not an m.g0 stack).  First it calls runtime.exitsyscall, which will
    62  // block until the $GOMAXPROCS limit allows running this goroutine.
    63  // Once exitsyscall has returned, it is safe to do things like call the memory
    64  // allocator or invoke the Go callback function.  runtime.cgocallbackg
    65  // first defers a function to unwind m.g0.sched.sp, so that if p.GoF
    66  // panics, m.g0.sched.sp will be restored to its old value: the m.g0 stack
    67  // and the m.curg stack will be unwound in lock step.
    68  // Then it calls _cgoexp_GoF(frame).
    69  //
    70  // _cgoexp_GoF, which was generated by cmd/cgo, unpacks the arguments
    71  // from frame, calls p.GoF, writes the results back to frame, and
    72  // returns. Now we start unwinding this whole process.
    73  //
    74  // runtime.cgocallbackg pops but does not execute the deferred
    75  // function to unwind m.g0.sched.sp, calls runtime.entersyscall, and
    76  // returns to runtime.cgocallback.
    77  //
    78  // After it regains control, runtime.cgocallback switches back to
    79  // m.g0's stack (the pointer is still in m.g0.sched.sp), restores the old
    80  // m.g0.sched.sp value from the stack, and returns to crosscall2.
    81  //
    82  // crosscall2 restores the callee-save registers for gcc and returns
    83  // to GoF, which unpacks any result values and returns to f.
    84  
    85  package runtime
    86  
    87  import (
    88  	"runtime/internal/atomic"
    89  	"runtime/internal/sys"
    90  	"unsafe"
    91  )
    92  
    93  // Addresses collected in a cgo backtrace when crashing.
    94  // Length must match arg.Max in x_cgo_callers in runtime/cgo/gcc_traceback.c.
    95  type cgoCallers [32]uintptr
    96  
    97  // argset matches runtime/cgo/linux_syscall.c:argset_t
    98  type argset struct {
    99  	args   unsafe.Pointer
   100  	retval uintptr
   101  }
   102  
   103  // wrapper for syscall package to call cgocall for libc (cgo) calls.
   104  //go:linkname syscall_cgocaller syscall.cgocaller
   105  //go:nosplit
   106  //go:uintptrescapes
   107  func syscall_cgocaller(fn unsafe.Pointer, args ...uintptr) uintptr {
   108  	as := argset{args: unsafe.Pointer(&args[0])}
   109  	cgocall(fn, unsafe.Pointer(&as))
   110  	return as.retval
   111  }
   112  
   113  var ncgocall uint64 // number of cgo calls in total for dead m
   114  
   115  // Call from Go to C.
   116  //
   117  // This must be nosplit because it's used for syscalls on some
   118  // platforms. Syscalls may have untyped arguments on the stack, so
   119  // it's not safe to grow or scan the stack.
   120  //
   121  //go:nosplit
   122  func cgocall(fn, arg unsafe.Pointer) int32 {
   123  	if !iscgo && GOOS != "solaris" && GOOS != "illumos" && GOOS != "windows" {
   124  		throw("cgocall unavailable")
   125  	}
   126  
   127  	if fn == nil {
   128  		throw("cgocall nil")
   129  	}
   130  
   131  	if raceenabled {
   132  		racereleasemerge(unsafe.Pointer(&racecgosync))
   133  	}
   134  
   135  	mp := getg().m
   136  	mp.ncgocall++
   137  	mp.ncgo++
   138  
   139  	// Reset traceback.
   140  	mp.cgoCallers[0] = 0
   141  
   142  	// Announce we are entering a system call
   143  	// so that the scheduler knows to create another
   144  	// M to run goroutines while we are in the
   145  	// foreign code.
   146  	//
   147  	// The call to asmcgocall is guaranteed not to
   148  	// grow the stack and does not allocate memory,
   149  	// so it is safe to call while "in a system call", outside
   150  	// the $GOMAXPROCS accounting.
   151  	//
   152  	// fn may call back into Go code, in which case we'll exit the
   153  	// "system call", run the Go code (which may grow the stack),
   154  	// and then re-enter the "system call" reusing the PC and SP
   155  	// saved by entersyscall here.
   156  	entersyscall()
   157  
   158  	// Tell asynchronous preemption that we're entering external
   159  	// code. We do this after entersyscall because this may block
   160  	// and cause an async preemption to fail, but at this point a
   161  	// sync preemption will succeed (though this is not a matter
   162  	// of correctness).
   163  	osPreemptExtEnter(mp)
   164  
   165  	mp.incgo = true
   166  	errno := asmcgocall(fn, arg)
   167  
   168  	// Update accounting before exitsyscall because exitsyscall may
   169  	// reschedule us on to a different M.
   170  	mp.incgo = false
   171  	mp.ncgo--
   172  
   173  	osPreemptExtExit(mp)
   174  
   175  	exitsyscall()
   176  
   177  	// Note that raceacquire must be called only after exitsyscall has
   178  	// wired this M to a P.
   179  	if raceenabled {
   180  		raceacquire(unsafe.Pointer(&racecgosync))
   181  	}
   182  
   183  	// From the garbage collector's perspective, time can move
   184  	// backwards in the sequence above. If there's a callback into
   185  	// Go code, GC will see this function at the call to
   186  	// asmcgocall. When the Go call later returns to C, the
   187  	// syscall PC/SP is rolled back and the GC sees this function
   188  	// back at the call to entersyscall. Normally, fn and arg
   189  	// would be live at entersyscall and dead at asmcgocall, so if
   190  	// time moved backwards, GC would see these arguments as dead
   191  	// and then live. Prevent these undead arguments from crashing
   192  	// GC by forcing them to stay live across this time warp.
   193  	KeepAlive(fn)
   194  	KeepAlive(arg)
   195  	KeepAlive(mp)
   196  
   197  	return errno
   198  }
   199  
   200  // Call from C back to Go. fn must point to an ABIInternal Go entry-point.
   201  //go:nosplit
   202  func cgocallbackg(fn, frame unsafe.Pointer, ctxt uintptr) {
   203  	gp := getg()
   204  	if gp != gp.m.curg {
   205  		println("runtime: bad g in cgocallback")
   206  		exit(2)
   207  	}
   208  
   209  	// The call from C is on gp.m's g0 stack, so we must ensure
   210  	// that we stay on that M. We have to do this before calling
   211  	// exitsyscall, since it would otherwise be free to move us to
   212  	// a different M. The call to unlockOSThread is in unwindm.
   213  	lockOSThread()
   214  
   215  	checkm := gp.m
   216  
   217  	// Save current syscall parameters, so m.syscall can be
   218  	// used again if callback decide to make syscall.
   219  	syscall := gp.m.syscall
   220  
   221  	// entersyscall saves the caller's SP to allow the GC to trace the Go
   222  	// stack. However, since we're returning to an earlier stack frame and
   223  	// need to pair with the entersyscall() call made by cgocall, we must
   224  	// save syscall* and let reentersyscall restore them.
   225  	savedsp := unsafe.Pointer(gp.syscallsp)
   226  	savedpc := gp.syscallpc
   227  	exitsyscall() // coming out of cgo call
   228  	gp.m.incgo = false
   229  
   230  	osPreemptExtExit(gp.m)
   231  
   232  	cgocallbackg1(fn, frame, ctxt) // will call unlockOSThread
   233  
   234  	// At this point unlockOSThread has been called.
   235  	// The following code must not change to a different m.
   236  	// This is enforced by checking incgo in the schedule function.
   237  
   238  	gp.m.incgo = true
   239  
   240  	if gp.m != checkm {
   241  		throw("m changed unexpectedly in cgocallbackg")
   242  	}
   243  
   244  	osPreemptExtEnter(gp.m)
   245  
   246  	// going back to cgo call
   247  	reentersyscall(savedpc, uintptr(savedsp))
   248  
   249  	gp.m.syscall = syscall
   250  }
   251  
   252  func cgocallbackg1(fn, frame unsafe.Pointer, ctxt uintptr) {
   253  	gp := getg()
   254  
   255  	// When we return, undo the call to lockOSThread in cgocallbackg.
   256  	// We must still stay on the same m.
   257  	defer unlockOSThread()
   258  
   259  	if gp.m.needextram || atomic.Load(&extraMWaiters) > 0 {
   260  		gp.m.needextram = false
   261  		systemstack(newextram)
   262  	}
   263  
   264  	if ctxt != 0 {
   265  		s := append(gp.cgoCtxt, ctxt)
   266  
   267  		// Now we need to set gp.cgoCtxt = s, but we could get
   268  		// a SIGPROF signal while manipulating the slice, and
   269  		// the SIGPROF handler could pick up gp.cgoCtxt while
   270  		// tracing up the stack.  We need to ensure that the
   271  		// handler always sees a valid slice, so set the
   272  		// values in an order such that it always does.
   273  		p := (*slice)(unsafe.Pointer(&gp.cgoCtxt))
   274  		atomicstorep(unsafe.Pointer(&p.array), unsafe.Pointer(&s[0]))
   275  		p.cap = cap(s)
   276  		p.len = len(s)
   277  
   278  		defer func(gp *g) {
   279  			// Decrease the length of the slice by one, safely.
   280  			p := (*slice)(unsafe.Pointer(&gp.cgoCtxt))
   281  			p.len--
   282  		}(gp)
   283  	}
   284  
   285  	if gp.m.ncgo == 0 {
   286  		// The C call to Go came from a thread not currently running
   287  		// any Go. In the case of -buildmode=c-archive or c-shared,
   288  		// this call may be coming in before package initialization
   289  		// is complete. Wait until it is.
   290  		<-main_init_done
   291  	}
   292  
   293  	// Add entry to defer stack in case of panic.
   294  	restore := true
   295  	defer unwindm(&restore)
   296  
   297  	if raceenabled {
   298  		raceacquire(unsafe.Pointer(&racecgosync))
   299  	}
   300  
   301  	// Invoke callback. This function is generated by cmd/cgo and
   302  	// will unpack the argument frame and call the Go function.
   303  	var cb func(frame unsafe.Pointer)
   304  	cbFV := funcval{uintptr(fn)}
   305  	*(*unsafe.Pointer)(unsafe.Pointer(&cb)) = noescape(unsafe.Pointer(&cbFV))
   306  	cb(frame)
   307  
   308  	if raceenabled {
   309  		racereleasemerge(unsafe.Pointer(&racecgosync))
   310  	}
   311  
   312  	// Do not unwind m->g0->sched.sp.
   313  	// Our caller, cgocallback, will do that.
   314  	restore = false
   315  }
   316  
   317  func unwindm(restore *bool) {
   318  	if *restore {
   319  		// Restore sp saved by cgocallback during
   320  		// unwind of g's stack (see comment at top of file).
   321  		mp := acquirem()
   322  		sched := &mp.g0.sched
   323  		sched.sp = *(*uintptr)(unsafe.Pointer(sched.sp + alignUp(sys.MinFrameSize, sys.StackAlign)))
   324  
   325  		// Do the accounting that cgocall will not have a chance to do
   326  		// during an unwind.
   327  		//
   328  		// In the case where a Go call originates from C, ncgo is 0
   329  		// and there is no matching cgocall to end.
   330  		if mp.ncgo > 0 {
   331  			mp.incgo = false
   332  			mp.ncgo--
   333  			osPreemptExtExit(mp)
   334  		}
   335  
   336  		releasem(mp)
   337  	}
   338  }
   339  
   340  // called from assembly
   341  func badcgocallback() {
   342  	throw("misaligned stack in cgocallback")
   343  }
   344  
   345  // called from (incomplete) assembly
   346  func cgounimpl() {
   347  	throw("cgo not implemented")
   348  }
   349  
   350  var racecgosync uint64 // represents possible synchronization in C code
   351  
   352  // Pointer checking for cgo code.
   353  
   354  // We want to detect all cases where a program that does not use
   355  // unsafe makes a cgo call passing a Go pointer to memory that
   356  // contains a Go pointer. Here a Go pointer is defined as a pointer
   357  // to memory allocated by the Go runtime. Programs that use unsafe
   358  // can evade this restriction easily, so we don't try to catch them.
   359  // The cgo program will rewrite all possibly bad pointer arguments to
   360  // call cgoCheckPointer, where we can catch cases of a Go pointer
   361  // pointing to a Go pointer.
   362  
   363  // Complicating matters, taking the address of a slice or array
   364  // element permits the C program to access all elements of the slice
   365  // or array. In that case we will see a pointer to a single element,
   366  // but we need to check the entire data structure.
   367  
   368  // The cgoCheckPointer call takes additional arguments indicating that
   369  // it was called on an address expression. An additional argument of
   370  // true means that it only needs to check a single element. An
   371  // additional argument of a slice or array means that it needs to
   372  // check the entire slice/array, but nothing else. Otherwise, the
   373  // pointer could be anything, and we check the entire heap object,
   374  // which is conservative but safe.
   375  
   376  // When and if we implement a moving garbage collector,
   377  // cgoCheckPointer will pin the pointer for the duration of the cgo
   378  // call.  (This is necessary but not sufficient; the cgo program will
   379  // also have to change to pin Go pointers that cannot point to Go
   380  // pointers.)
   381  
   382  // cgoCheckPointer checks if the argument contains a Go pointer that
   383  // points to a Go pointer, and panics if it does.
   384  func cgoCheckPointer(ptr interface{}, arg interface{}) {
   385  	if debug.cgocheck == 0 {
   386  		return
   387  	}
   388  
   389  	ep := efaceOf(&ptr)
   390  	t := ep._type
   391  
   392  	top := true
   393  	if arg != nil && (t.kind&kindMask == kindPtr || t.kind&kindMask == kindUnsafePointer) {
   394  		p := ep.data
   395  		if t.kind&kindDirectIface == 0 {
   396  			p = *(*unsafe.Pointer)(p)
   397  		}
   398  		if p == nil || !cgoIsGoPointer(p) {
   399  			return
   400  		}
   401  		aep := efaceOf(&arg)
   402  		switch aep._type.kind & kindMask {
   403  		case kindBool:
   404  			if t.kind&kindMask == kindUnsafePointer {
   405  				// We don't know the type of the element.
   406  				break
   407  			}
   408  			pt := (*ptrtype)(unsafe.Pointer(t))
   409  			cgoCheckArg(pt.elem, p, true, false, cgoCheckPointerFail)
   410  			return
   411  		case kindSlice:
   412  			// Check the slice rather than the pointer.
   413  			ep = aep
   414  			t = ep._type
   415  		case kindArray:
   416  			// Check the array rather than the pointer.
   417  			// Pass top as false since we have a pointer
   418  			// to the array.
   419  			ep = aep
   420  			t = ep._type
   421  			top = false
   422  		default:
   423  			throw("can't happen")
   424  		}
   425  	}
   426  
   427  	cgoCheckArg(t, ep.data, t.kind&kindDirectIface == 0, top, cgoCheckPointerFail)
   428  }
   429  
   430  const cgoCheckPointerFail = "cgo argument has Go pointer to Go pointer"
   431  const cgoResultFail = "cgo result has Go pointer"
   432  
   433  // cgoCheckArg is the real work of cgoCheckPointer. The argument p
   434  // is either a pointer to the value (of type t), or the value itself,
   435  // depending on indir. The top parameter is whether we are at the top
   436  // level, where Go pointers are allowed.
   437  func cgoCheckArg(t *_type, p unsafe.Pointer, indir, top bool, msg string) {
   438  	if t.ptrdata == 0 || p == nil {
   439  		// If the type has no pointers there is nothing to do.
   440  		return
   441  	}
   442  
   443  	switch t.kind & kindMask {
   444  	default:
   445  		throw("can't happen")
   446  	case kindArray:
   447  		at := (*arraytype)(unsafe.Pointer(t))
   448  		if !indir {
   449  			if at.len != 1 {
   450  				throw("can't happen")
   451  			}
   452  			cgoCheckArg(at.elem, p, at.elem.kind&kindDirectIface == 0, top, msg)
   453  			return
   454  		}
   455  		for i := uintptr(0); i < at.len; i++ {
   456  			cgoCheckArg(at.elem, p, true, top, msg)
   457  			p = add(p, at.elem.size)
   458  		}
   459  	case kindChan, kindMap:
   460  		// These types contain internal pointers that will
   461  		// always be allocated in the Go heap. It's never OK
   462  		// to pass them to C.
   463  		panic(errorString(msg))
   464  	case kindFunc:
   465  		if indir {
   466  			p = *(*unsafe.Pointer)(p)
   467  		}
   468  		if !cgoIsGoPointer(p) {
   469  			return
   470  		}
   471  		panic(errorString(msg))
   472  	case kindInterface:
   473  		it := *(**_type)(p)
   474  		if it == nil {
   475  			return
   476  		}
   477  		// A type known at compile time is OK since it's
   478  		// constant. A type not known at compile time will be
   479  		// in the heap and will not be OK.
   480  		if inheap(uintptr(unsafe.Pointer(it))) {
   481  			panic(errorString(msg))
   482  		}
   483  		p = *(*unsafe.Pointer)(add(p, sys.PtrSize))
   484  		if !cgoIsGoPointer(p) {
   485  			return
   486  		}
   487  		if !top {
   488  			panic(errorString(msg))
   489  		}
   490  		cgoCheckArg(it, p, it.kind&kindDirectIface == 0, false, msg)
   491  	case kindSlice:
   492  		st := (*slicetype)(unsafe.Pointer(t))
   493  		s := (*slice)(p)
   494  		p = s.array
   495  		if p == nil || !cgoIsGoPointer(p) {
   496  			return
   497  		}
   498  		if !top {
   499  			panic(errorString(msg))
   500  		}
   501  		if st.elem.ptrdata == 0 {
   502  			return
   503  		}
   504  		for i := 0; i < s.cap; i++ {
   505  			cgoCheckArg(st.elem, p, true, false, msg)
   506  			p = add(p, st.elem.size)
   507  		}
   508  	case kindString:
   509  		ss := (*stringStruct)(p)
   510  		if !cgoIsGoPointer(ss.str) {
   511  			return
   512  		}
   513  		if !top {
   514  			panic(errorString(msg))
   515  		}
   516  	case kindStruct:
   517  		st := (*structtype)(unsafe.Pointer(t))
   518  		if !indir {
   519  			if len(st.fields) != 1 {
   520  				throw("can't happen")
   521  			}
   522  			cgoCheckArg(st.fields[0].typ, p, st.fields[0].typ.kind&kindDirectIface == 0, top, msg)
   523  			return
   524  		}
   525  		for _, f := range st.fields {
   526  			if f.typ.ptrdata == 0 {
   527  				continue
   528  			}
   529  			cgoCheckArg(f.typ, add(p, f.offset()), true, top, msg)
   530  		}
   531  	case kindPtr, kindUnsafePointer:
   532  		if indir {
   533  			p = *(*unsafe.Pointer)(p)
   534  			if p == nil {
   535  				return
   536  			}
   537  		}
   538  
   539  		if !cgoIsGoPointer(p) {
   540  			return
   541  		}
   542  		if !top {
   543  			panic(errorString(msg))
   544  		}
   545  
   546  		cgoCheckUnknownPointer(p, msg)
   547  	}
   548  }
   549  
   550  // cgoCheckUnknownPointer is called for an arbitrary pointer into Go
   551  // memory. It checks whether that Go memory contains any other
   552  // pointer into Go memory. If it does, we panic.
   553  // The return values are unused but useful to see in panic tracebacks.
   554  func cgoCheckUnknownPointer(p unsafe.Pointer, msg string) (base, i uintptr) {
   555  	if inheap(uintptr(p)) {
   556  		b, span, _ := findObject(uintptr(p), 0, 0)
   557  		base = b
   558  		if base == 0 {
   559  			return
   560  		}
   561  		hbits := heapBitsForAddr(base)
   562  		n := span.elemsize
   563  		for i = uintptr(0); i < n; i += sys.PtrSize {
   564  			if !hbits.morePointers() {
   565  				// No more possible pointers.
   566  				break
   567  			}
   568  			if hbits.isPointer() && cgoIsGoPointer(*(*unsafe.Pointer)(unsafe.Pointer(base + i))) {
   569  				panic(errorString(msg))
   570  			}
   571  			hbits = hbits.next()
   572  		}
   573  
   574  		return
   575  	}
   576  
   577  	for _, datap := range activeModules() {
   578  		if cgoInRange(p, datap.data, datap.edata) || cgoInRange(p, datap.bss, datap.ebss) {
   579  			// We have no way to know the size of the object.
   580  			// We have to assume that it might contain a pointer.
   581  			panic(errorString(msg))
   582  		}
   583  		// In the text or noptr sections, we know that the
   584  		// pointer does not point to a Go pointer.
   585  	}
   586  
   587  	return
   588  }
   589  
   590  // cgoIsGoPointer reports whether the pointer is a Go pointer--a
   591  // pointer to Go memory. We only care about Go memory that might
   592  // contain pointers.
   593  //go:nosplit
   594  //go:nowritebarrierrec
   595  func cgoIsGoPointer(p unsafe.Pointer) bool {
   596  	if p == nil {
   597  		return false
   598  	}
   599  
   600  	if inHeapOrStack(uintptr(p)) {
   601  		return true
   602  	}
   603  
   604  	for _, datap := range activeModules() {
   605  		if cgoInRange(p, datap.data, datap.edata) || cgoInRange(p, datap.bss, datap.ebss) {
   606  			return true
   607  		}
   608  	}
   609  
   610  	return false
   611  }
   612  
   613  // cgoInRange reports whether p is between start and end.
   614  //go:nosplit
   615  //go:nowritebarrierrec
   616  func cgoInRange(p unsafe.Pointer, start, end uintptr) bool {
   617  	return start <= uintptr(p) && uintptr(p) < end
   618  }
   619  
   620  // cgoCheckResult is called to check the result parameter of an
   621  // exported Go function. It panics if the result is or contains a Go
   622  // pointer.
   623  func cgoCheckResult(val interface{}) {
   624  	if debug.cgocheck == 0 {
   625  		return
   626  	}
   627  
   628  	ep := efaceOf(&val)
   629  	t := ep._type
   630  	cgoCheckArg(t, ep.data, t.kind&kindDirectIface == 0, false, cgoResultFail)
   631  }
   632  

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