github.com/zxy12/golang_with_comment@v0.0.0-20190701084843-0e6b2aff5ef3/runtime/mem_darwin.go (about)

     1  // Copyright 2010 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  // Don't split the stack as this function may be invoked without a valid G,
    10  // which prevents us from allocating more stack.
    11  //go:nosplit
    12  func sysAlloc(n uintptr, sysStat *uint64) unsafe.Pointer {
    13  	v := mmap(nil, n, _PROT_READ|_PROT_WRITE, _MAP_ANON|_MAP_PRIVATE, -1, 0)
    14  	if uintptr(v) < 4096 {
    15  		return nil
    16  	}
    17  	mSysStatInc(sysStat, n)
    18  	return v
    19  }
    20  
    21  func sysUnused(v unsafe.Pointer, n uintptr) {
    22  	// Linux's MADV_DONTNEED is like BSD's MADV_FREE.
    23  	madvise(v, n, _MADV_FREE)
    24  }
    25  
    26  func sysUsed(v unsafe.Pointer, n uintptr) {
    27  }
    28  
    29  // Don't split the stack as this function may be invoked without a valid G,
    30  // which prevents us from allocating more stack.
    31  //go:nosplit
    32  func sysFree(v unsafe.Pointer, n uintptr, sysStat *uint64) {
    33  	mSysStatDec(sysStat, n)
    34  	munmap(v, n)
    35  }
    36  
    37  func sysFault(v unsafe.Pointer, n uintptr) {
    38  	mmap(v, n, _PROT_NONE, _MAP_ANON|_MAP_PRIVATE|_MAP_FIXED, -1, 0)
    39  }
    40  
    41  func sysReserve(v unsafe.Pointer, n uintptr, reserved *bool) unsafe.Pointer {
    42  	*reserved = true
    43  	// 那是为了预留虚拟内存但不占用物理内存,后面会随着分配慢慢的调用mprotect改权限,再调用一次mmap，权限会换
    44  	p := mmap(v, n, _PROT_NONE, _MAP_ANON|_MAP_PRIVATE, -1, 0)
    45  	println("in sysReserve,p=", p, ",v=", v)
    46  	if uintptr(p) < 4096 {
    47  		return nil
    48  	}
    49  	return p
    50  }
    51  
    52  const (
    53  	_ENOMEM = 12
    54  )
    55  
    56  func sysMap(v unsafe.Pointer, n uintptr, reserved bool, sysStat *uint64) {
    57  	mSysStatInc(sysStat, n)
    58  	p := mmap(v, n, _PROT_READ|_PROT_WRITE, _MAP_ANON|_MAP_FIXED|_MAP_PRIVATE, -1, 0)
    59  	if uintptr(p) == _ENOMEM {
    60  		throw("runtime: out of memory")
    61  	}
    62  	if p != v {
    63  		throw("runtime: cannot map pages in arena address space")
    64  	}
    65  }