direct_mmap.h
Go to the documentation of this file.
1 // Copyright 2017 The Abseil Authors.
2 //
3 // Licensed under the Apache License, Version 2.0 (the "License");
4 // you may not use this file except in compliance with the License.
5 // You may obtain a copy of the License at
6 //
7 // https://www.apache.org/licenses/LICENSE-2.0
8 //
9 // Unless required by applicable law or agreed to in writing, software
10 // distributed under the License is distributed on an "AS IS" BASIS,
11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12 // See the License for the specific language governing permissions and
13 // limitations under the License.
14 //
15 // Functions for directly invoking mmap() via syscall, avoiding the case where
16 // mmap() has been locally overridden.
17 
18 #ifndef ABSL_BASE_INTERNAL_DIRECT_MMAP_H_
19 #define ABSL_BASE_INTERNAL_DIRECT_MMAP_H_
20 
21 #include "absl/base/config.h"
22 
23 #if ABSL_HAVE_MMAP
24 
25 #include <sys/mman.h>
26 
27 #ifdef __linux__
28 
29 #include <sys/types.h>
30 #ifdef __BIONIC__
31 #include <sys/syscall.h>
32 #else
33 #include <syscall.h>
34 #endif
35 
36 #include <linux/unistd.h>
37 #include <unistd.h>
38 #include <cerrno>
39 #include <cstdarg>
40 #include <cstdint>
41 
42 #ifdef __mips__
43 // Include definitions of the ABI currently in use.
44 #ifdef __BIONIC__
45 // Android doesn't have sgidefs.h, but does have asm/sgidefs.h, which has the
46 // definitions we need.
47 #include <asm/sgidefs.h>
48 #else
49 #include <sgidefs.h>
50 #endif // __BIONIC__
51 #endif // __mips__
52 
53 // SYS_mmap and SYS_munmap are not defined in Android.
54 #ifdef __BIONIC__
55 extern "C" void* __mmap2(void*, size_t, int, int, int, size_t);
56 #if defined(__NR_mmap) && !defined(SYS_mmap)
57 #define SYS_mmap __NR_mmap
58 #endif
59 #ifndef SYS_munmap
60 #define SYS_munmap __NR_munmap
61 #endif
62 #endif // __BIONIC__
63 
64 namespace absl {
65 namespace base_internal {
66 
67 // Platform specific logic extracted from
68 // https://chromium.googlesource.com/linux-syscall-support/+/master/linux_syscall_support.h
69 inline void* DirectMmap(void* start, size_t length, int prot, int flags, int fd,
70  off64_t offset) noexcept {
71 #if defined(__i386__) || defined(__ARM_ARCH_3__) || defined(__ARM_EABI__) || \
72  (defined(__mips__) && _MIPS_SIM == _MIPS_SIM_ABI32) || \
73  (defined(__PPC__) && !defined(__PPC64__)) || \
74  (defined(__s390__) && !defined(__s390x__))
75  // On these architectures, implement mmap with mmap2.
76  static int pagesize = 0;
77  if (pagesize == 0) {
78 #if defined(__wasm__) || defined(__asmjs__)
79  pagesize = getpagesize();
80 #else
81  pagesize = sysconf(_SC_PAGESIZE);
82 #endif
83  }
84  if (offset < 0 || offset % pagesize != 0) {
85  errno = EINVAL;
86  return MAP_FAILED;
87  }
88 #ifdef __BIONIC__
89  // SYS_mmap2 has problems on Android API level <= 16.
90  // Workaround by invoking __mmap2() instead.
91  return __mmap2(start, length, prot, flags, fd, offset / pagesize);
92 #else
93  return reinterpret_cast<void*>(
94  syscall(SYS_mmap2, start, length, prot, flags, fd,
95  static_cast<off_t>(offset / pagesize)));
96 #endif
97 #elif defined(__s390x__)
98  // On s390x, mmap() arguments are passed in memory.
99  unsigned long buf[6] = {reinterpret_cast<unsigned long>(start), // NOLINT
100  static_cast<unsigned long>(length), // NOLINT
101  static_cast<unsigned long>(prot), // NOLINT
102  static_cast<unsigned long>(flags), // NOLINT
103  static_cast<unsigned long>(fd), // NOLINT
104  static_cast<unsigned long>(offset)}; // NOLINT
105  return reinterpret_cast<void*>(syscall(SYS_mmap, buf));
106 #elif defined(__x86_64__)
107 // The x32 ABI has 32 bit longs, but the syscall interface is 64 bit.
108 // We need to explicitly cast to an unsigned 64 bit type to avoid implicit
109 // sign extension. We can't cast pointers directly because those are
110 // 32 bits, and gcc will dump ugly warnings about casting from a pointer
111 // to an integer of a different size. We also need to make sure __off64_t
112 // isn't truncated to 32-bits under x32.
113 #define MMAP_SYSCALL_ARG(x) ((uint64_t)(uintptr_t)(x))
114  return reinterpret_cast<void*>(
115  syscall(SYS_mmap, MMAP_SYSCALL_ARG(start), MMAP_SYSCALL_ARG(length),
116  MMAP_SYSCALL_ARG(prot), MMAP_SYSCALL_ARG(flags),
117  MMAP_SYSCALL_ARG(fd), static_cast<uint64_t>(offset)));
118 #undef MMAP_SYSCALL_ARG
119 #else // Remaining 64-bit aritectures.
120  static_assert(sizeof(unsigned long) == 8, "Platform is not 64-bit");
121  return reinterpret_cast<void*>(
122  syscall(SYS_mmap, start, length, prot, flags, fd, offset));
123 #endif
124 }
125 
126 inline int DirectMunmap(void* start, size_t length) {
127  return static_cast<int>(syscall(SYS_munmap, start, length));
128 }
129 
130 } // namespace base_internal
131 } // namespace absl
132 
133 #else // !__linux__
134 
135 // For non-linux platforms where we have mmap, just dispatch directly to the
136 // actual mmap()/munmap() methods.
137 
138 namespace absl {
139 namespace base_internal {
140 
141 inline void* DirectMmap(void* start, size_t length, int prot, int flags, int fd,
142  off_t offset) {
143  return mmap(start, length, prot, flags, fd, offset);
144 }
145 
146 inline int DirectMunmap(void* start, size_t length) {
147  return munmap(start, length);
148 }
149 
150 } // namespace base_internal
151 } // namespace absl
152 
153 #endif // __linux__
154 
155 #endif // ABSL_HAVE_MMAP
156 
157 #endif // ABSL_BASE_INTERNAL_DIRECT_MMAP_H_
char buf[N]
Definition: algorithm.h:29
std::size_t length
Definition: test_util.cc:52


abseil_cpp
Author(s):
autogenerated on Wed Jun 19 2019 19:19:56