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/__support/macros/config.h" 15 #include "src/errno/libc_errno.h" 16 #include <linux/param.h> // For EXEC_PAGESIZE. 17 #include <sys/syscall.h> // For syscall numbers. 18 19 namespace LIBC_NAMESPACE_DECL { 20 21 // This function is currently linux only. It has to be refactored suitably if 22 // mmap is to be supported on non-linux operating systems also. 23 LLVM_LIBC_FUNCTION(void *, mmap, 24 (void *addr, size_t size, int prot, int flags, int fd, 25 off_t offset)) { 26 // A lot of POSIX standard prescribed validation of the parameters is not 27 // done in this function as modern linux versions do it in the syscall. 28 // TODO: Perform argument validation not done by the linux syscall. 29 30 // EXEC_PAGESIZE is used for the page size. While this is OK for x86_64, it 31 // might not be correct in general. 32 // TODO: Use pagesize read from the ELF aux vector instead of EXEC_PAGESIZE. 33 34 #ifdef SYS_mmap2 35 offset /= EXEC_PAGESIZE; 36 long syscall_number = SYS_mmap2; 37 #elif defined(SYS_mmap) 38 long syscall_number = SYS_mmap; 39 #else 40 #error "mmap or mmap2 syscalls not available." 41 #endif 42 43 // We add an explicit cast to silence a "implicit conversion loses integer 44 // precision" warning when compiling for 32-bit systems. 45 long mmap_offset = static_cast<long>(offset); 46 long ret = 47 LIBC_NAMESPACE::syscall_impl(syscall_number, reinterpret_cast<long>(addr), 48 size, prot, flags, fd, mmap_offset); 49 50 // The mmap/mmap2 syscalls return negative values on error. These negative 51 // values are actually the negative values of the error codes. So, fix them 52 // up in case an error code is detected. 53 // 54 // A point to keep in mind for the fix up is that a negative return value 55 // from the syscall can also be an error-free value returned by the syscall. 56 // However, since a valid return address cannot be within the last page, a 57 // return value corresponding to a location in the last page is an error 58 // value. 59 if (ret < 0 && ret > -EXEC_PAGESIZE) { 60 libc_errno = static_cast<int>(-ret); 61 return MAP_FAILED; 62 } 63 64 return reinterpret_cast<void *>(ret); 65 } 66 67 } // namespace LIBC_NAMESPACE_DECL 68