cgo_mmap.go

     1  // Copyright 2015 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  // Support for memory sanitizer. See runtime/cgo/mmap.go.
     6  
     7  //go:build (linux && amd64) || (linux && arm64)
     8  
     9  package runtime
    10  
    11  import "unsafe"
    12  
    13  // _cgo_mmap is filled in by runtime/cgo when it is linked into the
    14  // program, so it is only non-nil when using cgo.
    15  //go:linkname _cgo_mmap _cgo_mmap
    16  var _cgo_mmap unsafe.Pointer
    17  
    18  // _cgo_munmap is filled in by runtime/cgo when it is linked into the
    19  // program, so it is only non-nil when using cgo.
    20  //go:linkname _cgo_munmap _cgo_munmap
    21  var _cgo_munmap unsafe.Pointer
    22  
    23  // mmap is used to route the mmap system call through C code when using cgo, to
    24  // support sanitizer interceptors. Don't allow stack splits, since this function
    25  // (used by sysAlloc) is called in a lot of low-level parts of the runtime and
    26  // callers often assume it won't acquire any locks.
    27  //go:nosplit
    28  func mmap(addr unsafe.Pointer, n uintptr, prot, flags, fd int32, off uint32) (unsafe.Pointer, int) {
    29  	if _cgo_mmap != nil {
    30  		// Make ret a uintptr so that writing to it in the
    31  		// function literal does not trigger a write barrier.
    32  		// A write barrier here could break because of the way
    33  		// that mmap uses the same value both as a pointer and
    34  		// an errno value.
    35  		var ret uintptr
    36  		systemstack(func() {
    37  			ret = callCgoMmap(addr, n, prot, flags, fd, off)
    38  		})
    39  		if ret < 4096 {
    40  			return nil, int(ret)
    41  		}
    42  		return unsafe.Pointer(ret), 0
    43  	}
    44  	return sysMmap(addr, n, prot, flags, fd, off)
    45  }
    46  
    47  func munmap(addr unsafe.Pointer, n uintptr) {
    48  	if _cgo_munmap != nil {
    49  		systemstack(func() { callCgoMunmap(addr, n) })
    50  		return
    51  	}
    52  	sysMunmap(addr, n)
    53  }
    54  
    55  // sysMmap calls the mmap system call. It is implemented in assembly.
    56  func sysMmap(addr unsafe.Pointer, n uintptr, prot, flags, fd int32, off uint32) (p unsafe.Pointer, err int)
    57  
    58  // callCgoMmap calls the mmap function in the runtime/cgo package
    59  // using the GCC calling convention. It is implemented in assembly.
    60  func callCgoMmap(addr unsafe.Pointer, n uintptr, prot, flags, fd int32, off uint32) uintptr
    61  
    62  // sysMunmap calls the munmap system call. It is implemented in assembly.
    63  func sysMunmap(addr unsafe.Pointer, n uintptr)
    64  
    65  // callCgoMunmap calls the munmap function in the runtime/cgo package
    66  // using the GCC calling convention. It is implemented in assembly.
    67  func callCgoMunmap(addr unsafe.Pointer, n uintptr)
    68
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