| 1 | //===---------- Linux implementation of the POSIX mmap function -----------===// |
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| 2 | // |
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| 3 | // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
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| 4 | // See https://llvm.org/LICENSE.txt for license information. |
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| 5 | // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
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| 6 | // |
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| 7 | //===----------------------------------------------------------------------===// |
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| 8 | |
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| 9 | #include "src/sys/mman/mmap.h" |
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| 10 | |
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| 11 | #include "src/__support/OSUtil/syscall.h" // For internal syscall function. |
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| 12 | #include "src/__support/common.h" |
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| 13 | |
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| 14 | #include "src/errno/libc_errno.h" |
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| 15 | #include <linux/param.h> // For EXEC_PAGESIZE. |
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| 16 | #include <sys/syscall.h> // For syscall numbers. |
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| 17 | |
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| 18 | namespace LIBC_NAMESPACE { |
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| 19 | |
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| 20 | // This function is currently linux only. It has to be refactored suitably if |
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| 21 | // mmap is to be supported on non-linux operating systems also. |
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| 22 | LLVM_LIBC_FUNCTION(void *, mmap, |
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| 23 | (void *addr, size_t size, int prot, int flags, int fd, |
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| 24 | off_t offset)) { |
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| 25 | // A lot of POSIX standard prescribed validation of the parameters is not |
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| 26 | // done in this function as modern linux versions do it in the syscall. |
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| 27 | // TODO: Perform argument validation not done by the linux syscall. |
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| 28 | |
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| 29 | // EXEC_PAGESIZE is used for the page size. While this is OK for x86_64, it |
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| 30 | // might not be correct in general. |
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| 31 | // TODO: Use pagesize read from the ELF aux vector instead of EXEC_PAGESIZE. |
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| 32 | |
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| 33 | #ifdef SYS_mmap2 |
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| 34 | offset /= EXEC_PAGESIZE; |
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| 35 | long syscall_number = SYS_mmap2; |
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| 36 | #elif defined(SYS_mmap) |
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| 37 | long syscall_number = SYS_mmap; |
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| 38 | #else |
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| 39 | #error "mmap or mmap2 syscalls not available." |
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| 40 | #endif |
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| 41 | |
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| 42 | long ret = |
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| 43 | LIBC_NAMESPACE::syscall_impl(number: syscall_number, arg1: reinterpret_cast<long>(addr), |
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| 44 | arg2: size, arg3: prot, arg4: flags, arg5: fd, arg6: offset); |
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| 45 | |
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| 46 | // The mmap/mmap2 syscalls return negative values on error. These negative |
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| 47 | // values are actually the negative values of the error codes. So, fix them |
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| 48 | // up in case an error code is detected. |
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| 49 | // |
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| 50 | // A point to keep in mind for the fix up is that a negative return value |
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| 51 | // from the syscall can also be an error-free value returned by the syscall. |
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| 52 | // However, since a valid return address cannot be within the last page, a |
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| 53 | // return value corresponding to a location in the last page is an error |
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| 54 | // value. |
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| 55 | if (ret < 0 && ret > -EXEC_PAGESIZE) { |
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| 56 | libc_errno = static_cast<int>(-ret); |
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| 57 | return MAP_FAILED; |
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| 58 | } |
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| 59 | |
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| 60 | return reinterpret_cast<void *>(ret); |
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| 61 | } |
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| 62 | |
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| 63 | } // namespace LIBC_NAMESPACE |
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| 64 | |
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