Make fixes and improvements

- Introduce __assert_disable global
- Improve strsignal() thread safety
- Make system call tracing thread safe
- Fix SO_RCVTIMEO / SO_SNDTIMEO on Windows
- Refactor DescribeFoo() functions into one place
- Fix fork() on Windows when TLS and MAP_STACK exist
- Round upwards in setsockopt(SO_RCVTIMEO) on Windows
- Disable futexes on OpenBSD which seem extremely broken
- Implement a better kludge for monotonic time on Windows

libc/runtime/mprotect.c

@@ -0,0 +1,58 @@
+/*-*- 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/bits/likely.h"
+#include "libc/calls/strace.internal.h"
+#include "libc/calls/syscall-sysv.internal.h"
+#include "libc/dce.h"
+#include "libc/errno.h"
+#include "libc/intrin/describeflags.internal.h"
+#include "libc/intrin/kprintf.h"
+#include "libc/runtime/internal.h"
+#include "libc/runtime/runtime.h"
+#include "libc/sysv/consts/prot.h"
+#include "libc/sysv/errfuns.h"
+
+/**
+ * Modifies restrictions on virtual memory address range.
+ *
+ * @param addr needs to be 4kb aligned
+ * @param prot can have PROT_{NONE,READ,WRITE,EXEC,GROWSDOWN,GROWSUP}
+ * @return 0 on success, or -1 w/ errno
+ * @see mmap()
+ */
+int mprotect(void *addr, size_t size, int prot) {
+  int64_t rc;
+  if (SupportsWindows() && (prot & ~(PROT_READ | PROT_WRITE | PROT_EXEC |
+                                     PROT_GROWSDOWN | PROT_GROWSUP))) {
+    errno = EINVAL;  // unix checks prot before checking size
+    rc = -1;
+  } else if (!size) {
+    return 0;  // make new technology consistent with unix
+  } else if (UNLIKELY((intptr_t)addr & 4095)) {
+    errno = EINVAL;  // unix checks prot before checking size
+    rc = -1;
+  } else if (!IsWindows()) {
+    rc = sys_mprotect(addr, size, prot);
+  } else {
+    rc = sys_mprotect_nt(addr, size, prot);
+  }
+  STRACE("mprotect(%p, %'zu, %s) → %d% m", addr, size, DescribeProtFlags(prot),
+         rc);
+  return rc;
+}