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// Userspace emulation of mmap and munmap. Restrictions apply.
//
// This is meant to be complete enough to be compatible with code that uses
// mmap for simple file I/O. It just allocates memory with malloc and reads
// and writes data with pread and pwrite.
#define _WASI_EMULATED_MMAN
#include <stdlib.h>
#include <errno.h>
#include <unistd.h>
#include <string.h>
#include <sys/mman.h>
#include <sys/types.h>
struct map {
int prot;
int flags;
off_t offset;
size_t length;
};
void *mmap(void *addr, size_t length, int prot, int flags,
int fd, off_t offset) {
// Check for unsupported flags.
if ((flags & (MAP_PRIVATE | MAP_SHARED)) == 0 ||
(flags & MAP_FIXED) != 0 ||
#ifdef MAP_SHARED_VALIDATE
(flags & MAP_SHARED_VALIDATE) == MAP_SHARED_VALIDATE ||
#endif
#ifdef MAP_NORESERVE
(flags & MAP_NORESERVE) != 0 ||
#endif
#ifdef MAP_GROWSDOWN
(flags & MAP_GROWSDOWN) != 0 ||
#endif
#ifdef MAP_HUGETLB
(flags & MAP_HUGETLB) != 0 ||
#endif
#ifdef MAP_FIXED_NOREPLACE
(flags & MAP_FIXED_NOREPLACE) != 0 ||
#endif
0)
{
errno = EINVAL;
return MAP_FAILED;
}
// Check for unsupported protection requests.
if (prot == PROT_NONE ||
#ifdef PROT_EXEC
(prot & PROT_EXEC) != 0 ||
#endif
0)
{
errno = EINVAL;
return MAP_FAILED;
}
// To be consistent with POSIX.
if (length == 0) {
errno = EINVAL;
return MAP_FAILED;
}
// Check for integer overflow.
size_t buf_len = 0;
if (__builtin_add_overflow(length, sizeof(struct map), &buf_len)) {
errno = ENOMEM;
return MAP_FAILED;
}
// Allocate the memory.
struct map *map = malloc(buf_len);
if (!map) {
errno = ENOMEM;
return MAP_FAILED;
}
// Initialize the header.
map->prot = prot;
map->flags = flags;
map->offset = offset;
map->length = length;
// Initialize the main memory buffer, either with the contents of a file,
// or with zeros.
addr = map + 1;
if ((flags & MAP_ANON) == 0) {
char *body = (char *)addr;
while (length > 0) {
const ssize_t nread = pread(fd, body, length, offset);
if (nread < 0) {
if (errno == EINTR)
continue;
return MAP_FAILED;
}
if (nread == 0)
break;
length -= (size_t)nread;
offset += (size_t)nread;
body += (size_t)nread;
}
} else {
memset(addr, 0, length);
}
return addr;
}
int munmap(void *addr, size_t length) {
struct map *map = (struct map *)addr - 1;
// We don't support partial munmapping.
if (map->length != length) {
errno = EINVAL;
return -1;
}
// Release the memory.
free(map);
// Success!
return 0;
}
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