Fix bugs and add security features to redbean

- Fix a regression with the previous change that broke redbean
- Add chroot(), resource limit, seccomp, and other stuff to redbean
- Write lots and lots of documentation
- Iron out more system call issues

libc/thread/exit.c

@@ -16,28 +16,31 @@
 │ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
 │ PERFORMANCE OF THIS SOFTWARE.                                                │
 ╚─────────────────────────────────────────────────────────────────────────────*/
-#include "libc/sysv/consts/nr.h"
+#include "libc/calls/internal.h"
+#include "libc/calls/strace.internal.h"
+#include "libc/intrin/lockxadd.h"
+#include "libc/runtime/runtime.h"
 #include "libc/thread/descriptor.h"
 #include "libc/thread/exit.h"
 #include "libc/thread/self.h"
 
+/**
+ * Exits cosmopolitan thread.
+ *
+ * @param rc is exit code
+ * @see _Exit1() for the raw system call
+ * @threadsafe
+ * @noreturn
+ */
 wontreturn void cthread_exit(int rc) {
-  cthread_t td = cthread_self();
+  cthread_t td;
+  STRACE("cthread_exit(%d)", rc);
+  td = cthread_self();
   td->rc = rc;
-  size_t size = (intptr_t)(td->alloc.top) - (intptr_t)(td->alloc.bottom);
-
-  int state;
-  asm volatile("lock xadd\t%1, %0\n\t"      // mark thread as finished
-               "test\t%2, %b1\n\t"          // test if thread was detached
-               "jz .L.cthread_exit.%=\n\t"  // skip unmap if not detached
-               "syscall\n"                  // unmap thread
-               ".L.cthread_exit.%=:\n\t"
-               "mov\t%%rbx, %%rdi\n\t"  // rc
-               "mov\t$60, %%rax\n\t"
-               "syscall"  // thread exit
-               : "+m"(td->state), "=&r"(state)
-               : "I"(cthread_detached), "1"(cthread_finished), "a"(__NR_munmap),
-                 "b"(rc), "D"(td->alloc.bottom), "S"(size)
-               : "rcx", "r11", "cc", "memory");
-  unreachable;
+  _lockxadd(&td->state, cthread_finished);
+  if (~td->state & cthread_detached) {
+    sys_munmap(td->alloc.bottom,
+               (intptr_t)td->alloc.top - (intptr_t)td->alloc.bottom);
+  }
+  _Exit1(rc);
 }