diff --git a/libc/bionic/scandir.cpp b/libc/bionic/scandir.cpp
index f528286..0acef36 100644
--- a/libc/bionic/scandir.cpp
+++ b/libc/bionic/scandir.cpp
@@ -69,11 +69,8 @@
   }
 
   void Sort(int (*comparator)(const dirent**, const dirent**)) {
-    // If we have entries and a comparator, sort them.
-    if (size_ > 0 && comparator != nullptr) {
-      qsort(names_, size_, sizeof(dirent*),
-            reinterpret_cast<int (*)(const void*, const void*)>(comparator));
-    }
+    qsort(names_, size_, sizeof(dirent*),
+          reinterpret_cast<int (*)(const void*, const void*)>(comparator));
   }
 
  private:
@@ -120,7 +117,9 @@
     names.Add(entry);
   }
 
-  names.Sort(comparator);
+  if (comparator != nullptr) {
+    names.Sort(comparator);
+  }
 
   size_t size = names.size();
   *name_list = names.release();
diff --git a/libc/bionic/spawn.cpp b/libc/bionic/spawn.cpp
index 7e80ef6..5cf95d8 100644
--- a/libc/bionic/spawn.cpp
+++ b/libc/bionic/spawn.cpp
@@ -340,7 +340,7 @@
   if (action == nullptr) return errno;
 
   action->next = nullptr;
-  if (path != nullptr) {
+  if (what == kOpen) {
     action->path = strdup(path);
     if (action->path == nullptr) {
       free(action);
diff --git a/libc/include/dirent.h b/libc/include/dirent.h
index 2328b1a..2751b9e 100644
--- a/libc/include/dirent.h
+++ b/libc/include/dirent.h
@@ -95,7 +95,7 @@
  *
  * Returns null and sets `errno` on failure.
  */
-DIR* opendir(const char* __path);
+DIR* _Nullable opendir(const char* _Nonnull __path);
 
 /**
  * [fopendir(3)](http://man7.org/linux/man-pages/man3/opendir.3.html)
@@ -103,7 +103,7 @@
  *
  * Returns null and sets `errno` on failure.
  */
-DIR* fdopendir(int __dir_fd);
+DIR* _Nullable fdopendir(int __dir_fd);
 
 /**
  * [readdir(3)](http://man7.org/linux/man-pages/man3/readdir.3.html)
@@ -113,7 +113,7 @@
  * or returns null and leaves `errno` unchanged at the end of the directory,
  * or returns null and sets `errno` on failure.
  */
-struct dirent* readdir(DIR* __dir);
+struct dirent* _Nullable readdir(DIR* _Nonnull __dir);
 
 /**
  * [readdir64(3)](http://man7.org/linux/man-pages/man3/readdir.3.html)
@@ -123,10 +123,10 @@
  * or returns null and leaves `errno` unchanged at the end of the directory,
  * or returns null and sets `errno` on failure.
  */
-struct dirent64* readdir64(DIR* __dir) __INTRODUCED_IN(21);
+struct dirent64* _Nullable readdir64(DIR* _Nonnull __dir) __INTRODUCED_IN(21);
 
-int readdir_r(DIR* __dir, struct dirent* __entry, struct dirent** __buffer) __attribute__((__deprecated__("readdir_r is deprecated; use readdir instead")));
-int readdir64_r(DIR* __dir, struct dirent64* __entry, struct dirent64** __buffer) __INTRODUCED_IN(21) __attribute__((__deprecated__("readdir64_r is deprecated; use readdir64 instead")));
+int readdir_r(DIR* _Nonnull __dir, struct dirent* _Nonnull __entry, struct dirent* _Nullable * _Nonnull __buffer) __attribute__((__deprecated__("readdir_r is deprecated; use readdir instead")));
+int readdir64_r(DIR* _Nonnull __dir, struct dirent64* _Nonnull __entry, struct dirent64* _Nullable * _Nonnull __buffer) __INTRODUCED_IN(21) __attribute__((__deprecated__("readdir64_r is deprecated; use readdir64 instead")));
 
 /**
  * [closedir(3)](http://man7.org/linux/man-pages/man3/closedir.3.html)
@@ -134,13 +134,13 @@
  *
  * Returns 0 on success and returns -1 and sets `errno` on failure.
  */
-int closedir(DIR* __dir);
+int closedir(DIR* _Nonnull __dir);
 
 /**
  * [rewinddir(3)](http://man7.org/linux/man-pages/man3/rewinddir.3.html)
  * rewinds a directory stream to the first entry.
  */
-void rewinddir(DIR* __dir);
+void rewinddir(DIR* _Nonnull __dir);
 
 /**
  * [seekdir(3)](http://man7.org/linux/man-pages/man3/seekdir.3.html)
@@ -149,7 +149,7 @@
  *
  * Available since API level 23.
  */
-void seekdir(DIR* __dir, long __location) __INTRODUCED_IN(23);
+void seekdir(DIR* _Nonnull __dir, long __location) __INTRODUCED_IN(23);
 
 /**
  * [telldir(3)](http://man7.org/linux/man-pages/man3/telldir.3.html)
@@ -160,7 +160,7 @@
  *
  * Available since API level 23.
  */
-long telldir(DIR* __dir) __INTRODUCED_IN(23);
+long telldir(DIR* _Nonnull __dir) __INTRODUCED_IN(23);
 
 /**
  * [dirfd(3)](http://man7.org/linux/man-pages/man3/dirfd.3.html)
@@ -168,13 +168,13 @@
  *
  * Returns a file descriptor on success and returns -1 and sets `errno` on failure.
  */
-int dirfd(DIR* __dir);
+int dirfd(DIR* _Nonnull __dir);
 
 /**
  * [alphasort](http://man7.org/linux/man-pages/man3/alphasort.3.html) is a
  * comparator for use with scandir() that uses strcoll().
  */
-int alphasort(const struct dirent** __lhs, const struct dirent** __rhs);
+int alphasort(const struct dirent* _Nonnull * _Nonnull __lhs, const struct dirent* _Nonnull * _Nonnull __rhs);
 
 /**
  * [alphasort64](http://man7.org/linux/man-pages/man3/alphasort.3.html) is a
@@ -182,31 +182,33 @@
  *
  * Available since API level 21.
  */
-int alphasort64(const struct dirent64** __lhs, const struct dirent64** __rhs) __INTRODUCED_IN(21);
+int alphasort64(const struct dirent64* _Nonnull * _Nonnull __lhs, const struct dirent64* _Nonnull * _Nonnull __rhs) __INTRODUCED_IN(21);
 
 /**
  * [scandir(3)](http://man7.org/linux/man-pages/man3/scandir.3.html)
  * scans all the directory `__path`, filtering entries with `__filter` and
  * sorting them with qsort() using the given `__comparator`, and storing them
  * into `__name_list`. Passing NULL as the filter accepts all entries.
+ * Passing NULL as the comparator skips sorting.
  *
  * Returns the number of entries returned in the list on success,
  * and returns -1 and sets `errno` on failure.
  */
-int scandir(const char* __path, struct dirent*** __name_list, int (*__filter)(const struct dirent*), int (*__comparator)(const struct dirent**, const struct dirent**));
+int scandir(const char* _Nonnull __path, struct dirent* _Nonnull * _Nonnull * _Nonnull __name_list, int (* _Nullable __filter)(const struct dirent* _Nonnull), int (* _Nullable __comparator)(const struct dirent* _Nonnull * _Nonnull, const struct dirent* _Nonnull * _Nonnull));
 
 /**
  * [scandir64(3)](http://man7.org/linux/man-pages/man3/scandir.3.html)
  * scans all the directory `__path`, filtering entries with `__filter` and
  * sorting them with qsort() using the given `__comparator`, and storing them
  * into `__name_list`. Passing NULL as the filter accepts all entries.
+ * Passing NULL as the comparator skips sorting.
  *
  * Returns the number of entries returned in the list on success,
  * and returns -1 and sets `errno` on failure.
  *
  * Available since API level 21.
  */
-int scandir64(const char* __path, struct dirent64*** __name_list, int (*__filter)(const struct dirent64*), int (*__comparator)(const struct dirent64**, const struct dirent64**)) __INTRODUCED_IN(21);
+int scandir64(const char* _Nonnull __path, struct dirent64* _Nonnull * _Nonnull * _Nonnull __name_list, int (* _Nullable __filter)(const struct dirent64* _Nonnull), int (* _Nullable __comparator)(const struct dirent64* _Nonnull * _Nonnull, const struct dirent64* _Nonnull * _Nonnull)) __INTRODUCED_IN(21);
 
 #if defined(__USE_GNU)
 
@@ -216,13 +218,14 @@
  * filtering entries with `__filter` and sorting them with qsort() using the
  * given `__comparator`, and storing them into `__name_list`. Passing NULL as
  * the filter accepts all entries.
+ * Passing NULL as the comparator skips sorting.
  *
  * Returns the number of entries returned in the list on success,
  * and returns -1 and sets `errno` on failure.
  *
  * Available since API level 24.
  */
-int scandirat64(int __dir_fd, const char* __path, struct dirent64*** __name_list, int (*__filter)(const struct dirent64*), int (*__comparator)(const struct dirent64**, const struct dirent64**)) __INTRODUCED_IN(24);
+int scandirat64(int __dir_fd, const char* _Nonnull __path, struct dirent64* _Nonnull * _Nonnull * _Nonnull __name_list, int (* _Nullable __filter)(const struct dirent64* _Nonnull), int (* _Nullable __comparator)(const struct dirent64* _Nonnull * _Nonnull, const struct dirent64* _Nonnull * _Nonnull)) __INTRODUCED_IN(24);
 
 /**
  * [scandirat(3)](http://man7.org/linux/man-pages/man3/scandirat.3.html)
@@ -230,13 +233,14 @@
  * filtering entries with `__filter` and sorting them with qsort() using the
  * given `__comparator`, and storing them into `__name_list`. Passing NULL as
  * the filter accepts all entries.
+ * Passing NULL as the comparator skips sorting.
  *
  * Returns the number of entries returned in the list on success,
  * and returns -1 and sets `errno` on failure.
  *
  * Available since API level 24.
  */
-int scandirat(int __dir_fd, const char* __path, struct dirent*** __name_list, int (*__filter)(const struct dirent*), int (*__comparator)(const struct dirent**, const struct dirent**)) __INTRODUCED_IN(24);
+int scandirat(int __dir_fd, const char* _Nonnull __path, struct dirent* _Nonnull * _Nonnull * _Nonnull __name_list, int (* _Nullable __filter)(const struct dirent* _Nonnull), int (* _Nullable __comparator)(const struct dirent* _Nonnull * _Nonnull, const struct dirent* _Nonnull * _Nonnull)) __INTRODUCED_IN(24);
 
 #endif
 
diff --git a/libc/include/fts.h b/libc/include/fts.h
index 7e63111..bae2615 100644
--- a/libc/include/fts.h
+++ b/libc/include/fts.h
@@ -39,15 +39,15 @@
 #include <sys/types.h>
 
 typedef struct {
-	struct _ftsent *fts_cur;	/* current node */
-	struct _ftsent *fts_child;	/* linked list of children */
-	struct _ftsent **fts_array;	/* sort array */
+	struct _ftsent * _Nullable fts_cur;	/* current node */
+	struct _ftsent * _Nullable fts_child;	/* linked list of children */
+	struct _ftsent * _Nullable * _Nullable fts_array;	/* sort array */
 	dev_t fts_dev;			/* starting device # */
-	char *fts_path;			/* path for this descent */
+	char * _Nullable fts_path;			/* path for this descent */
 	int fts_rfd;			/* fd for root */
 	size_t fts_pathlen;		/* sizeof(path) */
 	int fts_nitems;			/* elements in the sort array */
-	int (*fts_compar)();		/* compare function */
+	int (* _Nullable fts_compar)();		/* compare function */
 
 #define	FTS_COMFOLLOW	0x0001		/* follow command line symlinks */
 #define	FTS_LOGICAL	0x0002		/* logical walk */
@@ -65,13 +65,13 @@
 } FTS;
 
 typedef struct _ftsent {
-	struct _ftsent *fts_cycle;	/* cycle node */
-	struct _ftsent *fts_parent;	/* parent directory */
-	struct _ftsent *fts_link;	/* next file in directory */
+	struct _ftsent * _Nullable fts_cycle;	/* cycle node */
+	struct _ftsent * _Nullable fts_parent;	/* parent directory */
+	struct _ftsent * _Nullable fts_link;	/* next file in directory */
 	long fts_number;	        /* local numeric value */
-	void *fts_pointer;	        /* local address value */
-	char *fts_accpath;		/* access path */
-	char *fts_path;			/* root path */
+	void * _Nullable fts_pointer;	        /* local address value */
+	char * _Nullable fts_accpath;		/* access path */
+	char * _Nullable fts_path;			/* root path */
 	int fts_errno;			/* errno for this node */
 	int fts_symfd;			/* fd for symlink */
 	size_t fts_pathlen;		/* strlen(fts_path) */
@@ -111,7 +111,7 @@
 #define	FTS_SKIP	 4		/* discard node */
 	unsigned short fts_instr;	/* fts_set() instructions */
 
-	struct stat *fts_statp;		/* stat(2) information */
+	struct stat * _Nullable fts_statp;		/* stat(2) information */
 	char fts_name[1];		/* file name */
 } FTSENT;
 
@@ -122,11 +122,11 @@
  * breakage in 21 that means you can't write code that runs on current devices and pre-21 devices,
  * so we break the tie in favor of current and future devices.
  */
-FTSENT* fts_children(FTS* __fts, int __options) __INTRODUCED_IN(21);
-int fts_close(FTS* __fts) __INTRODUCED_IN(21);
-FTS* fts_open(char* const* __path, int __options, int (*__comparator)(const FTSENT** __lhs, const FTSENT** __rhs)) __INTRODUCED_IN(21);
-FTSENT* fts_read(FTS* __fts) __INTRODUCED_IN(21);
-int fts_set(FTS* __fts, FTSENT* __entry, int __options) __INTRODUCED_IN(21);
+FTSENT* _Nullable fts_children(FTS* _Nonnull __fts, int __options) __INTRODUCED_IN(21);
+int fts_close(FTS* _Nonnull __fts) __INTRODUCED_IN(21);
+FTS* _Nullable fts_open(char* _Nonnull const* _Nonnull __path, int __options, int (* _Nullable __comparator)(const FTSENT* _Nonnull * _Nonnull  __lhs, const FTSENT* _Nonnull * _Nonnull __rhs)) __INTRODUCED_IN(21);
+FTSENT* _Nullable fts_read(FTS* _Nonnull __fts) __INTRODUCED_IN(21);
+int fts_set(FTS* _Nonnull __fts, FTSENT* _Nonnull __entry, int __options) __INTRODUCED_IN(21);
 
 __END_DECLS
 
diff --git a/libc/include/sched.h b/libc/include/sched.h
index 364ca10..26bc742 100644
--- a/libc/include/sched.h
+++ b/libc/include/sched.h
@@ -104,7 +104,7 @@
  *
  * Returns 0 on success and returns -1 and sets `errno` on failure.
  */
-int sched_setscheduler(pid_t __pid, int __policy, const struct sched_param* __param);
+int sched_setscheduler(pid_t __pid, int __policy, const struct sched_param* _Nonnull __param);
 
 /**
  * [sched_getscheduler(2)](http://man7.org/linux/man-pages/man2/sched_getcpu.2.html)
@@ -145,7 +145,7 @@
  *
  * Returns 0 on success and returns -1 and sets `errno` on failure.
  */
-int sched_setparam(pid_t __pid, const struct sched_param* __param);
+int sched_setparam(pid_t __pid, const struct sched_param* _Nonnull __param);
 
 /**
  * [sched_getparam(2)](http://man7.org/linux/man-pages/man2/sched_getparam.2.html)
@@ -153,7 +153,7 @@
  *
  * Returns 0 on success and returns -1 and sets `errno` on failure.
  */
-int sched_getparam(pid_t __pid, struct sched_param* __param);
+int sched_getparam(pid_t __pid, struct sched_param* _Nonnull __param);
 
 /**
  * [sched_rr_get_interval(2)](http://man7.org/linux/man-pages/man2/sched_rr_get_interval.2.html)
@@ -161,7 +161,7 @@
  *
  * Returns 0 on success and returns -1 and sets `errno` on failure.
  */
-int sched_rr_get_interval(pid_t __pid, struct timespec* __quantum);
+int sched_rr_get_interval(pid_t __pid, struct timespec* _Nonnull __quantum);
 
 #if defined(__USE_GNU)
 
@@ -172,7 +172,7 @@
  * Returns the pid of the child to the caller on success and
  * returns -1 and sets `errno` on failure.
  */
-int clone(int (*__fn)(void*), void* __child_stack, int __flags, void* __arg, ...) __INTRODUCED_IN_ARM(9) __INTRODUCED_IN_X86(17);
+int clone(int (* __BIONIC_COMPLICATED_NULLNESS __fn)(void* __BIONIC_COMPLICATED_NULLNESS ), void* __BIONIC_COMPLICATED_NULLNESS __child_stack, int __flags, void* _Nullable __arg, ...) __INTRODUCED_IN_ARM(9) __INTRODUCED_IN_X86(17);
 
 /**
  * [unshare(2)](http://man7.org/linux/man-pages/man2/unshare.2.html)
@@ -228,7 +228,7 @@
  *
  * Returns 0 on success and returns -1 and sets `errno` on failure.
  */
-int sched_setaffinity(pid_t __pid, size_t __set_size, const cpu_set_t* __set);
+int sched_setaffinity(pid_t __pid, size_t __set_size, const cpu_set_t* _Nonnull __set);
 
 /**
  * [sched_getaffinity(2)](http://man7.org/linux/man-pages/man2/sched_getaffinity.2.html)
@@ -236,7 +236,7 @@
  *
  * Returns 0 on success and returns -1 and sets `errno` on failure.
  */
-int sched_getaffinity(pid_t __pid, size_t __set_size, cpu_set_t* __set);
+int sched_getaffinity(pid_t __pid, size_t __set_size, cpu_set_t* _Nonnull __set);
 
 /**
  * [CPU_ZERO](https://man7.org/linux/man-pages/man3/CPU_SET.3.html) clears all
@@ -308,7 +308,7 @@
  * how many bits are set in a dynamic CPU set allocated by `CPU_ALLOC`.
  */
 #define CPU_COUNT_S(setsize, set)  __sched_cpucount((setsize), (set))
-int __sched_cpucount(size_t __set_size, const cpu_set_t* __set);
+int __sched_cpucount(size_t __set_size, const cpu_set_t* _Nonnull __set);
 
 /**
  * [CPU_EQUAL](https://man7.org/linux/man-pages/man3/CPU_SET.3.html) tests
@@ -379,14 +379,14 @@
  * allocates a CPU set large enough for CPUs in the range 0..count-1.
  */
 #define CPU_ALLOC(count)  __sched_cpualloc((count))
-cpu_set_t* __sched_cpualloc(size_t __count);
+cpu_set_t* _Nullable __sched_cpualloc(size_t __count);
 
 /**
  * [CPU_FREE](https://man7.org/linux/man-pages/man3/CPU_SET.3.html)
  * deallocates a CPU set allocated by `CPU_ALLOC`.
  */
 #define CPU_FREE(set)     __sched_cpufree((set))
-void __sched_cpufree(cpu_set_t* __set);
+void __sched_cpufree(cpu_set_t* _Nonnull __set);
 
 #endif /* __USE_GNU */
 
diff --git a/libc/include/stdlib.h b/libc/include/stdlib.h
index b416f62..2bcb870 100644
--- a/libc/include/stdlib.h
+++ b/libc/include/stdlib.h
@@ -91,7 +91,7 @@
 
 void* _Nullable bsearch(const void* _Nonnull __key, const void* _Nullable __base, size_t __nmemb, size_t __size, int (* _Nonnull __comparator)(const void* _Nonnull __lhs, const void* _Nonnull __rhs));
 
-void qsort(void* _Nullable __base, size_t __nmemb, size_t __size, int (* _Nonnull __comparator)(const void* _Nonnull __lhs, const void* _Nonnull __rhs));
+void qsort(void* _Nullable __base, size_t __nmemb, size_t __size, int (* _Nonnull __comparator)(const void* _Nullable __lhs, const void* _Nullable __rhs));
 
 uint32_t arc4random(void);
 uint32_t arc4random_uniform(uint32_t __upper_bound);
diff --git a/libc/include/sys/ucontext.h b/libc/include/sys/ucontext.h
index cefe177..bb6443b 100644
--- a/libc/include/sys/ucontext.h
+++ b/libc/include/sys/ucontext.h
@@ -366,9 +366,9 @@
 
 /* This matches the kernel <asm/ucontext.h> but using mcontext_t. */
 
-typedef struct ucontext_t {
+typedef struct ucontext {
   unsigned long uc_flags;
-  struct ucontext_t* uc_link;
+  struct ucontext* uc_link;
   stack_t uc_stack;
   union {
     sigset_t uc_sigmask;
diff --git a/tests/sched_test.cpp b/tests/sched_test.cpp
index 03e8062..fa1a07f 100644
--- a/tests/sched_test.cpp
+++ b/tests/sched_test.cpp
@@ -303,5 +303,8 @@
 }
 
 TEST(sched, sched_getaffinity_failure) {
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wnonnull"
   ASSERT_EQ(-1, sched_getaffinity(getpid(), 0, nullptr));
+#pragma clang diagnostic pop
 }