1 //===---------- Linux implementation of the POSIX mmap function -----------===// 2 // 3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 4 // See https://llvm.org/LICENSE.txt for license information. 5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 6 // 7 //===----------------------------------------------------------------------===// 8 9 #include "src/sys/mman/mmap.h" 10 11 #include "src/__support/OSUtil/syscall.h" // For internal syscall function. 12 #include "src/__support/common.h" 13 14 #include "src/errno/libc_errno.h" 15 #include <linux/param.h> // For EXEC_PAGESIZE. 16 #include <sys/syscall.h> // For syscall numbers. 17 18 namespace LIBC_NAMESPACE { 19 20 // This function is currently linux only. It has to be refactored suitably if 21 // mmap is to be supported on non-linux operating systems also. 22 LLVM_LIBC_FUNCTION(void *, mmap, 23 (void *addr, size_t size, int prot, int flags, int fd, 24 off_t offset)) { 25 // A lot of POSIX standard prescribed validation of the parameters is not 26 // done in this function as modern linux versions do it in the syscall. 27 // TODO: Perform argument validation not done by the linux syscall. 28 29 // EXEC_PAGESIZE is used for the page size. While this is OK for x86_64, it 30 // might not be correct in general. 31 // TODO: Use pagesize read from the ELF aux vector instead of EXEC_PAGESIZE. 32 33 #ifdef SYS_mmap2 34 offset /= EXEC_PAGESIZE; 35 long syscall_number = SYS_mmap2; 36 #elif defined(SYS_mmap) 37 long syscall_number = SYS_mmap; 38 #else 39 #error "mmap or mmap2 syscalls not available." 40 #endif 41 42 long ret = 43 LIBC_NAMESPACE::syscall_impl(syscall_number, reinterpret_cast<long>(addr), 44 size, prot, flags, fd, offset); 45 46 // The mmap/mmap2 syscalls return negative values on error. These negative 47 // values are actually the negative values of the error codes. So, fix them 48 // up in case an error code is detected. 49 // 50 // A point to keep in mind for the fix up is that a negative return value 51 // from the syscall can also be an error-free value returned by the syscall. 52 // However, since a valid return address cannot be within the last page, a 53 // return value corresponding to a location in the last page is an error 54 // value. 55 if (ret < 0 && ret > -EXEC_PAGESIZE) { 56 libc_errno = static_cast<int>(-ret); 57 return MAP_FAILED; 58 } 59 60 return reinterpret_cast<void *>(ret); 61 } 62 63 } // namespace LIBC_NAMESPACE 64