1 files changed, 124 insertions, 0 deletions
diff --git a/libc-bottom-half/mman/mman.c b/libc-bottom-half/mman/mman.c
new file mode 100644
index 0000000..f02b136
--- /dev/null
+++ b/libc-bottom-half/mman/mman.c
@@ -0,0 +1,124 @@
+// 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;
+}