Userland: Statically allocate the buffer for readdir

Not sure if this is 100% POSIX compliant, because we invalidate the
directory entry with each 'readdir' call, but who cares.

Std/MemoryAllocator.cpp

@@ -36,6 +36,7 @@ namespace Std
                 entry->m_next = nullptr;
                 entry->m_size = round_to_word(size);
 
+                VERIFY(usize(entry->m_data) % 4 == 0);
                 return entry->m_data;
             }
 

Userland/LibC/dirent.c

@@ -18,16 +18,14 @@ DIR* opendir(const char *path)
 
 struct dirent* readdir(DIR *dirp)
 {
-    struct dirent *entry = malloc(sizeof(struct dirent));
-
-    ssize_t retval = read(dirp->fd, entry, sizeof(struct dirent));
+    ssize_t retval = read(dirp->fd, &dirp->entry, sizeof(struct dirent));
 
     if (retval == 0)
         return NULL;
 
     assert(retval == sizeof(struct dirent));
 
-    return entry;
+    return &dirp->entry;
 }
 
 int closedir(DIR *dirp)

Userland/LibC/dirent.h

@@ -5,6 +5,9 @@
 
 typedef struct {
     int fd;
+
+    // We return a pointer to this in each readdir call
+    struct dirent entry;
 } DIR;
 
 DIR* opendir(const char *path);