[clang] fix a few warnings

Mostly dealing with comparing a pointer variable that is declared
nonnull, which I find to be a dubious warning but is pretty safe in this
case since the compiler will be more aggressive about the nullness of
the arguments.

kernel/vm/pmm.c

@@ -34,7 +34,7 @@ static mutex_t lock = MUTEX_INITIAL_VALUE(lock);
 #define ADDRESS_IN_ARENA(address, arena) \
     ((address) >= (arena)->base && (address) <= (arena)->base + (arena)->size - 1)
 
-struct list_node *get_arena_list() { return &arena_list; }
+struct list_node *get_arena_list(void) { return &arena_list; }
 
 static inline bool page_is_free(const vm_page_t *page) {
     return !(page->flags & VM_PAGE_FLAG_NONFREE);

kernel/vm/vmm.c

@@ -298,8 +298,6 @@ status_t vmm_reserve_space(vmm_aspace_t *aspace, const char *name, size_t size,
     if (!name)
         name = "";
 
-    if (!aspace)
-        return ERR_INVALID_ARGS;
     if (size == 0)
         return NO_ERROR;
     if (!IS_PAGE_ALIGNED(vaddr) || !IS_PAGE_ALIGNED(size))
@@ -339,8 +337,6 @@ status_t vmm_alloc_physical(vmm_aspace_t *aspace, const char *name, size_t size,
     if (!name)
         name = "";
 
-    if (!aspace)
-        return ERR_INVALID_ARGS;
     if (size == 0)
         return NO_ERROR;
     if (!IS_PAGE_ALIGNED(paddr) || !IS_PAGE_ALIGNED(size))

lib/fs/fs.c

@@ -276,7 +276,7 @@ status_t fs_open_file(const char *path, filehandle **handle) {
 status_t fs_file_ioctl(filehandle *handle, int request, void *argp) {
     LTRACEF("filehandle %p, request %d, argp, %p\n", handle, request, argp);
 
-    if (unlikely(!handle || !handle->mount ||
+    if (unlikely(!handle->mount ||
                  !handle->mount->api || !handle->mount->api->file_ioctl)) {
         return ERR_INVALID_ARGS;
     }
@@ -322,9 +322,6 @@ status_t fs_create_file(const char *path, filehandle **handle, uint64_t len) {
 status_t fs_truncate_file(filehandle *handle, uint64_t len) {
     LTRACEF("filehandle %p, length %llu\n", handle, len);
 
-    if (unlikely(!handle))
-        return ERR_INVALID_ARGS;
-
     return handle->mount->api->truncate(handle->cookie, len);
 }
 
@@ -461,10 +458,6 @@ status_t fs_close_dir(dirhandle *handle) {
 status_t fs_stat_fs(const char *mountpoint, struct fs_stat *stat) {
     LTRACEF("mountpoint %s stat %p\n", mountpoint, stat);
 
-    if (!stat) {
-        return ERR_INVALID_ARGS;
-    }
-
     const char *newpath;
     struct fs_mount *mount = find_mount(mountpoint, &newpath);
     if (!mount) {

lib/libc/qsort.c

@@ -50,6 +50,10 @@ static __inline void     swapfunc(char *, char *, int, int);
         } while (--i > 0);              \
 }
 
+#if defined(__clang__)
+#pragma clang diagnostic ignored "-Wnull-pointer-subtraction"
+#endif
+
 #define SWAPINIT(a, es) swaptype = ((char *)a - (char *)0) % sizeof(long) || \
     es % sizeof(long) ? 2 : es == sizeof(long)? 0 : 1;