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//===---------- Linux implementation of the POSIX mmap function -----------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#include "src/sys/mman/mmap.h"
#include "src/__support/OSUtil/syscall.h" // For internal syscall function.
#include "src/__support/common.h"
#include "src/__support/libc_errno.h"
#include "src/__support/macros/config.h"
#include <linux/param.h> // For EXEC_PAGESIZE.
#include <sys/syscall.h> // For syscall numbers.
namespace LIBC_NAMESPACE_DECL {
// This function is currently linux only. It has to be refactored suitably if
// mmap is to be supported on non-linux operating systems also.
LLVM_LIBC_FUNCTION(void *, mmap,
(void *addr, size_t size, int prot, int flags, int fd,
off_t offset)) {
// A lot of POSIX standard prescribed validation of the parameters is not
// done in this function as modern linux versions do it in the syscall.
// TODO: Perform argument validation not done by the linux syscall.
// EXEC_PAGESIZE is used for the page size. While this is OK for x86_64, it
// might not be correct in general.
// TODO: Use pagesize read from the ELF aux vector instead of EXEC_PAGESIZE.
#ifdef SYS_mmap2
offset /= EXEC_PAGESIZE;
long syscall_number = SYS_mmap2;
#elif defined(SYS_mmap)
long syscall_number = SYS_mmap;
#else
#error "mmap or mmap2 syscalls not available."
#endif
// We add an explicit cast to silence a "implicit conversion loses integer
// precision" warning when compiling for 32-bit systems.
long mmap_offset = static_cast<long>(offset);
long ret =
LIBC_NAMESPACE::syscall_impl(syscall_number, reinterpret_cast<long>(addr),
size, prot, flags, fd, mmap_offset);
// The mmap/mmap2 syscalls return negative values on error. These negative
// values are actually the negative values of the error codes. So, fix them
// up in case an error code is detected.
//
// A point to keep in mind for the fix up is that a negative return value
// from the syscall can also be an error-free value returned by the syscall.
// However, since a valid return address cannot be within the last page, a
// return value corresponding to a location in the last page is an error
// value.
if (!linux_utils::is_valid_mmap(ret)) {
libc_errno = static_cast<int>(-ret);
return MAP_FAILED;
}
return reinterpret_cast<void *>(ret);
}
} // namespace LIBC_NAMESPACE_DECL
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