cgo.go

     1  // Copyright 2014 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  package runtime
     6  
     7  import "unsafe"
     8  
     9  //go:cgo_export_static main
    10  
    11  // Filled in by runtime/cgo when linked into binary.
    12  
    13  //go:linkname _cgo_init _cgo_init
    14  //go:linkname _cgo_thread_start _cgo_thread_start
    15  //go:linkname _cgo_sys_thread_create _cgo_sys_thread_create
    16  //go:linkname _cgo_notify_runtime_init_done _cgo_notify_runtime_init_done
    17  //go:linkname _cgo_callers _cgo_callers
    18  //go:linkname _cgo_set_context_function _cgo_set_context_function
    19  //go:linkname _cgo_yield _cgo_yield
    20  
    21  var (
    22  	_cgo_init                     unsafe.Pointer
    23  	_cgo_thread_start             unsafe.Pointer
    24  	_cgo_sys_thread_create        unsafe.Pointer
    25  	_cgo_notify_runtime_init_done unsafe.Pointer
    26  	_cgo_callers                  unsafe.Pointer
    27  	_cgo_set_context_function     unsafe.Pointer
    28  	_cgo_yield                    unsafe.Pointer
    29  )
    30  
    31  // iscgo is set to true by the runtime/cgo package
    32  var iscgo bool
    33  
    34  // cgoHasExtraM is set on startup when an extra M is created for cgo.
    35  // The extra M must be created before any C/C++ code calls cgocallback.
    36  var cgoHasExtraM bool
    37  
    38  // cgoUse is called by cgo-generated code (using go:linkname to get at
    39  // an unexported name). The calls serve two purposes:
    40  // 1) they are opaque to escape analysis, so the argument is considered to
    41  // escape to the heap.
    42  // 2) they keep the argument alive until the call site; the call is emitted after
    43  // the end of the (presumed) use of the argument by C.
    44  // cgoUse should not actually be called (see cgoAlwaysFalse).
    45  func cgoUse(any) { throw("cgoUse should not be called") }
    46  
    47  // cgoAlwaysFalse is a boolean value that is always false.
    48  // The cgo-generated code says if cgoAlwaysFalse { cgoUse(p) }.
    49  // The compiler cannot see that cgoAlwaysFalse is always false,
    50  // so it emits the test and keeps the call, giving the desired
    51  // escape analysis result. The test is cheaper than the call.
    52  var cgoAlwaysFalse bool
    53  
    54  var cgo_yield = &_cgo_yield
    55
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