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__
55extern "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
64namespace absl {
65namespace base_internal {
66
67// Platform specific logic extracted from
68// https://chromium.googlesource.com/linux-syscall-support/+/master/linux_syscall_support.h
69inline 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
126inline 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
138namespace absl {
139namespace base_internal {
140
141inline 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
146inline 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_
158