| 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/libc_errno.h" |
|---|
| 15 | #include "src/__support/macros/config.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 | |
|---|
