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 ( 8 "unsafe" 9 ) 10 11 const ( 12 _MEM_COMMIT = 0x1000 13 _MEM_RESERVE = 0x2000 14 _MEM_DECOMMIT = 0x4000 15 _MEM_RELEASE = 0x8000 16 17 _PAGE_READWRITE = 0x0004 18 _PAGE_NOACCESS = 0x0001 19 ) 20 21 // Don't split the stack as this function may be invoked without a valid G, 22 // which prevents us from allocating more stack. 23 //go:nosplit 24 func sysAlloc(n uintptr, sysStat *uint64) unsafe.Pointer { 25 mSysStatInc(sysStat, n) 26 return unsafe.Pointer(stdcall4(_VirtualAlloc, 0, n, _MEM_COMMIT|_MEM_RESERVE, _PAGE_READWRITE)) 27 } 28 29 func sysUnused(v unsafe.Pointer, n uintptr) { 30 r := stdcall3(_VirtualFree, uintptr(v), n, _MEM_DECOMMIT) 31 if r != 0 { 32 return 33 } 34 35 // Decommit failed. Usual reason is that we've merged memory from two different 36 // VirtualAlloc calls, and Windows will only let each VirtualFree handle pages from 37 // a single VirtualAlloc. It is okay to specify a subset of the pages from a single alloc, 38 // just not pages from multiple allocs. This is a rare case, arising only when we're 39 // trying to give memory back to the operating system, which happens on a time 40 // scale of minutes. It doesn't have to be terribly fast. Instead of extra bookkeeping 41 // on all our VirtualAlloc calls, try freeing successively smaller pieces until 42 // we manage to free something, and then repeat. This ends up being O(n log n) 43 // in the worst case, but that's fast enough. 44 for n > 0 { 45 small := n 46 for small >= 4096 && stdcall3(_VirtualFree, uintptr(v), small, _MEM_DECOMMIT) == 0 { 47 small /= 2 48 small &^= 4096 - 1 49 } 50 if small < 4096 { 51 throw("runtime: failed to decommit pages") 52 } 53 v = add(v, small) 54 n -= small 55 } 56 } 57 58 func sysUsed(v unsafe.Pointer, n uintptr) { 59 r := stdcall4(_VirtualAlloc, uintptr(v), n, _MEM_COMMIT, _PAGE_READWRITE) 60 if r != uintptr(v) { 61 throw("runtime: failed to commit pages") 62 } 63 64 // Commit failed. See SysUnused. 65 for n > 0 { 66 small := n 67 for small >= 4096 && stdcall4(_VirtualAlloc, uintptr(v), small, _MEM_COMMIT, _PAGE_READWRITE) == 0 { 68 small /= 2 69 small &^= 4096 - 1 70 } 71 if small < 4096 { 72 throw("runtime: failed to decommit pages") 73 } 74 v = add(v, small) 75 n -= small 76 } 77 } 78 79 // Don't split the stack as this function may be invoked without a valid G, 80 // which prevents us from allocating more stack. 81 //go:nosplit 82 func sysFree(v unsafe.Pointer, n uintptr, sysStat *uint64) { 83 mSysStatDec(sysStat, n) 84 r := stdcall3(_VirtualFree, uintptr(v), 0, _MEM_RELEASE) 85 if r == 0 { 86 throw("runtime: failed to release pages") 87 } 88 } 89 90 func sysFault(v unsafe.Pointer, n uintptr) { 91 // SysUnused makes the memory inaccessible and prevents its reuse 92 sysUnused(v, n) 93 } 94 95 func sysReserve(v unsafe.Pointer, n uintptr, reserved *bool) unsafe.Pointer { 96 *reserved = true 97 // v is just a hint. 98 // First try at v. 99 v = unsafe.Pointer(stdcall4(_VirtualAlloc, uintptr(v), n, _MEM_RESERVE, _PAGE_READWRITE)) 100 if v != nil { 101 return v 102 } 103 104 // Next let the kernel choose the address. 105 return unsafe.Pointer(stdcall4(_VirtualAlloc, 0, n, _MEM_RESERVE, _PAGE_READWRITE)) 106 } 107 108 func sysMap(v unsafe.Pointer, n uintptr, reserved bool, sysStat *uint64) { 109 mSysStatInc(sysStat, n) 110 p := stdcall4(_VirtualAlloc, uintptr(v), n, _MEM_COMMIT, _PAGE_READWRITE) 111 if p != uintptr(v) { 112 throw("runtime: cannot map pages in arena address space") 113 } 114 } 115
