mmap_win32.c

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/* mmap() replacement for Windows
 *
 * Author: Mike Frysinger <vapier@gentoo.org>
 * Placed into the public domain
 */

/* References:
 * CreateFileMapping: http://msdn.microsoft.com/en-us/library/aa366537(VS.85).aspx
 * CloseHandle:       http://msdn.microsoft.com/en-us/library/ms724211(VS.85).aspx
 * MapViewOfFile:     http://msdn.microsoft.com/en-us/library/aa366761(VS.85).aspx
 * UnmapViewOfFile:   http://msdn.microsoft.com/en-us/library/aa366882(VS.85).aspx
 */
#if defined(__MINGW32__) || defined(_WIN32)
#include <io.h>
#include <windows.h>
#include "mmap.h"

#ifdef __USE_FILE_OFFSET64
# define DWORD_HI(x) (x >> 32)
# define DWORD_LO(x) ((x) & 0xffffffff)
#else
# define DWORD_HI(x) (0)
# define DWORD_LO(x) (x)
#endif

#define UNUSED(x) (void)(x)

void* mmap(void* start, size_t length, int prot, int flags, int fd, off_t offset)
{
        UNUSED(start);
        UNUSED(length);

        if (prot & ~(PROT_READ | PROT_WRITE | PROT_EXEC))
                return MAP_FAILED;
        if (fd == -1) {
                if (!(flags & MAP_ANON) || offset)
                        return MAP_FAILED;
        } else if (flags & MAP_ANON)
                return MAP_FAILED;

        DWORD flProtect;
        if (prot & PROT_WRITE) {
                if (prot & PROT_EXEC)
                        flProtect = PAGE_EXECUTE_READWRITE;
                else
                        flProtect = PAGE_READWRITE;
        } else if (prot & PROT_EXEC) {
                if (prot & PROT_READ)
                        flProtect = PAGE_EXECUTE_READ;
                else if (prot & PROT_EXEC)
                        flProtect = PAGE_EXECUTE;
        } else
                flProtect = PAGE_READONLY;

        off_t end = length + offset;
        HANDLE mmap_fd, h;
        if (fd == -1)
                mmap_fd = INVALID_HANDLE_VALUE;
        else
                mmap_fd = (HANDLE)_get_osfhandle(fd);
        h = CreateFileMapping(mmap_fd, NULL, flProtect, DWORD_HI(end), DWORD_LO(end), NULL);
        if (h == NULL)
                return MAP_FAILED;

        DWORD dwDesiredAccess;
        if (prot & PROT_WRITE)
                dwDesiredAccess = FILE_MAP_WRITE;
        else
                dwDesiredAccess = FILE_MAP_READ;
        if (prot & PROT_EXEC)
                dwDesiredAccess |= FILE_MAP_EXECUTE;
        if (flags & MAP_PRIVATE)
                dwDesiredAccess |= FILE_MAP_COPY;
        void *ret = MapViewOfFile(h, dwDesiredAccess, DWORD_HI(offset), DWORD_LO(offset), length);
        if (ret == NULL) {
                ret = MAP_FAILED;
        }
        // since we are handling the file ourselves with fd, close the Windows Handle here
        CloseHandle(h);
        return ret;
}

void munmap(void* addr, size_t length)
{
        UNUSED(length);

        UnmapViewOfFile(addr);
}

#undef DWORD_HI
#undef DWORD_LO

#endif