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// Copyright 2017 The Abseil Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
// Functions for directly invoking mmap() via syscall, avoiding the case where
// mmap() has been locally overridden.
#ifndef ABSL_BASE_INTERNAL_DIRECT_MMAP_H_
#define ABSL_BASE_INTERNAL_DIRECT_MMAP_H_
#include "absl/base/config.h"
#if ABSL_HAVE_MMAP
#include <sys/mman.h>
#ifdef __linux__
#include <sys/types.h>
#ifdef __BIONIC__
#include <sys/syscall.h>
#else
#include <syscall.h>
#endif
#include <linux/unistd.h>
#include <unistd.h>
#include <cerrno>
#include <cstdarg>
#include <cstdint>
#ifdef __mips__
// Include definitions of the ABI currently in use.
#ifdef __BIONIC__
// Android doesn't have sgidefs.h, but does have asm/sgidefs.h, which has the
// definitions we need.
#include <asm/sgidefs.h>
#else
#include <sgidefs.h>
#endif // __BIONIC__
#endif // __mips__
// SYS_mmap and SYS_munmap are not defined in Android.
#ifdef __BIONIC__
extern "C" void* __mmap2(void*, size_t, int, int, int, size_t);
#if defined(__NR_mmap) && !defined(SYS_mmap)
#define SYS_mmap __NR_mmap
#endif
#ifndef SYS_munmap
#define SYS_munmap __NR_munmap
#endif
#endif // __BIONIC__
namespace absl {
namespace base_internal {
// Platform specific logic extracted from
// https://chromium.googlesource.com/linux-syscall-support/+/master/linux_syscall_support.h
inline void* DirectMmap(void* start, size_t length, int prot, int flags, int fd,
off64_t offset) noexcept {
#if defined(__i386__) || defined(__ARM_ARCH_3__) || defined(__ARM_EABI__) || \
(defined(__mips__) && _MIPS_SIM == _MIPS_SIM_ABI32) || \
(defined(__PPC__) && !defined(__PPC64__)) || \
(defined(__s390__) && !defined(__s390x__))
// On these architectures, implement mmap with mmap2.
static int pagesize = 0;
if (pagesize == 0) {
#if defined(__wasm__) || defined(__asmjs__)
pagesize = getpagesize();
#else
pagesize = sysconf(_SC_PAGESIZE);
#endif
}
if (offset < 0 || offset % pagesize != 0) {
errno = EINVAL;
return MAP_FAILED;
}
#ifdef __BIONIC__
// SYS_mmap2 has problems on Android API level <= 16.
// Workaround by invoking __mmap2() instead.
return __mmap2(start, length, prot, flags, fd, offset / pagesize);
#else
return reinterpret_cast<void*>(
syscall(SYS_mmap2, start, length, prot, flags, fd,
static_cast<off_t>(offset / pagesize)));
#endif
#elif defined(__s390x__)
// On s390x, mmap() arguments are passed in memory.
unsigned long buf[6] = {reinterpret_cast<unsigned long>(start), // NOLINT
static_cast<unsigned long>(length), // NOLINT
static_cast<unsigned long>(prot), // NOLINT
static_cast<unsigned long>(flags), // NOLINT
static_cast<unsigned long>(fd), // NOLINT
static_cast<unsigned long>(offset)}; // NOLINT
return reinterpret_cast<void*>(syscall(SYS_mmap, buf));
#elif defined(__x86_64__)
// The x32 ABI has 32 bit longs, but the syscall interface is 64 bit.
// We need to explicitly cast to an unsigned 64 bit type to avoid implicit
// sign extension. We can't cast pointers directly because those are
// 32 bits, and gcc will dump ugly warnings about casting from a pointer
// to an integer of a different size. We also need to make sure __off64_t
// isn't truncated to 32-bits under x32.
#define MMAP_SYSCALL_ARG(x) ((uint64_t)(uintptr_t)(x))
return reinterpret_cast<void*>(
syscall(SYS_mmap, MMAP_SYSCALL_ARG(start), MMAP_SYSCALL_ARG(length),
MMAP_SYSCALL_ARG(prot), MMAP_SYSCALL_ARG(flags),
MMAP_SYSCALL_ARG(fd), static_cast<uint64_t>(offset)));
#undef MMAP_SYSCALL_ARG
#else // Remaining 64-bit aritectures.
static_assert(sizeof(unsigned long) == 8, "Platform is not 64-bit");
return reinterpret_cast<void*>(
syscall(SYS_mmap, start, length, prot, flags, fd, offset));
#endif
}
inline int DirectMunmap(void* start, size_t length) {
return static_cast<int>(syscall(SYS_munmap, start, length));
}
} // namespace base_internal
} // namespace absl
#else // !__linux__
// For non-linux platforms where we have mmap, just dispatch directly to the
// actual mmap()/munmap() methods.
namespace absl {
namespace base_internal {
inline void* DirectMmap(void* start, size_t length, int prot, int flags, int fd,
off_t offset) {
return mmap(start, length, prot, flags, fd, offset);
}
inline int DirectMunmap(void* start, size_t length) {
return munmap(start, length);
}
} // namespace base_internal
} // namespace absl
#endif // __linux__
#endif // ABSL_HAVE_MMAP
#endif // ABSL_BASE_INTERNAL_DIRECT_MMAP_H_
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