Make fork() go 30% faster

This change makes fork() go nearly as fast as sys_fork() on UNIX. As for
Windows this change shaves about 4-5ms off fork() + wait() latency. This
is accomplished by using WriteProcessMemory() from the parent process to
setup the address space of a suspended process; it is better than a pipe

libc/intrin/virtualprotectex.c

@@ -0,0 +1,43 @@
+/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
+│ vi: set et ft=c ts=2 sts=2 sw=2 fenc=utf-8                               :vi │
+╞══════════════════════════════════════════════════════════════════════════════╡
+│ Copyright 2022 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/syscall_support-nt.internal.h"
+#include "libc/intrin/describeflags.h"
+#include "libc/intrin/strace.h"
+#include "libc/log/libfatal.internal.h"
+#include "libc/nt/memory.h"
+
+__msabi extern typeof(VirtualProtectEx) *const __imp_VirtualProtectEx;
+
+/**
+ * Protects memory on the New Technology.
+ * @note this wrapper takes care of ABI, STRACE(), and __winerr()
+ */
+textwindows bool32 VirtualProtectEx(int64_t hProcess, void *lpAddress,
+                                    uint64_t dwSize, uint32_t flNewProtect,
+                                    uint32_t *lpflOldProtect) {
+  bool32 bOk;
+  bOk = __imp_VirtualProtectEx(hProcess, lpAddress, dwSize, flNewProtect,
+                               lpflOldProtect);
+  if (!bOk)
+    __winerr();
+  NTTRACE("VirtualProtectEx(%ld, %p, %'zu, %s, [%s]) → %hhhd% m", hProcess,
+          lpAddress, dwSize, DescribeNtPageFlags(flNewProtect),
+          DescribeNtPageFlags(*lpflOldProtect), bOk);
+  return bOk;
+}