Improve locks and signals

- Introduce fast spinlock API
- Double rand64() perf w/ spinlock
- Improve raise() on New Technology
- Support gettid() across platforms
- Implement SA_NODEFER on New Technology
- Move the lock intrinsics into LIBC_INTRIN
- Make SIGTRAP recoverable on New Technology
- Block SIGCHLD in wait4() on New Technology
- Add threading prototypes for XNU and FreeBSD
- Rewrite abort() fixing its minor bugs on XNU/NT
- Shave down a lot of the content in libc/bits/bits.h
- Let signal handlers modify CPU registers on New Technology

libc/intrin/gettid.c

@@ -0,0 +1,78 @@
+/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
+│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8                                :vi│
+╞══════════════════════════════════════════════════════════════════════════════╡
+│ Copyright 2020 Justine Alexandra Roberts Tunney                              │
+│                                                                              │
+│ Permission to use, copy, modify, and/or distribute this software for         │
+│ any purpose with or without fee is hereby granted, provided that the         │
+│ above copyright notice and this permission notice appear in all copies.      │
+│                                                                              │
+│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL                │
+│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED                │
+│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE             │
+│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL         │
+│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR        │
+│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER               │
+│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
+│ PERFORMANCE OF THIS SOFTWARE.                                                │
+╚─────────────────────────────────────────────────────────────────────────────*/
+#include "libc/calls/calls.h"
+#include "libc/dce.h"
+#include "libc/nt/thread.h"
+
+/**
+ * Returns current thread id.
+ * @asyncsignalsafe
+ */
+int gettid(void) {
+  int rc;
+  int64_t wut;
+
+  if (IsLinux()) {
+    asm("syscall"
+        : "=a"(rc)  // man says always succeeds
+        : "0"(186)  // __NR_gettid
+        : "rcx", "r11", "memory");
+    return rc;
+  }
+
+  if (IsXnu()) {
+    asm("syscall"              // xnu/osfmk/kern/ipc_tt.c
+        : "=a"(rc)             // assume success
+        : "0"(0x1000000 | 27)  // Mach thread_self_trap()
+        : "rcx", "r11", "memory", "cc");
+    return rc;
+  }
+
+  if (IsOpenbsd()) {
+    asm("syscall"
+        : "=a"(rc)  // man says always succeeds
+        : "0"(299)  // getthrid()
+        : "rcx", "r11", "memory", "cc");
+    return rc;
+  }
+
+  if (IsNetbsd()) {
+    asm("syscall"
+        : "=a"(rc)  // man says always succeeds
+        : "0"(311)  // _lwp_self()
+        : "rcx", "r11", "memory", "cc");
+    return rc;
+  }
+
+  if (IsFreebsd()) {
+    asm("syscall"
+        : "=a"(rc),  // only fails w/ EFAULT, which isn't possible
+          "=m"(wut)  // must be 64-bit
+        : "0"(432),  // thr_self()
+          "D"(&wut)  // but not actually 64-bit
+        : "rcx", "r11", "memory", "cc");
+    return wut;  // narrowing intentional
+  }
+
+  if (IsWindows()) {
+    return GetCurrentThreadId();
+  }
+
+  return getpid();
+}