Make signal handling work well across platforms

- Fix sigsuspend() on XNU
- Fix strsignal() on non-Linux
- Add unit tests for strsignal()
- Add unit tests for setitimer()
- Add unit tests for sigsuspend()
- Rewrite setitimer() for New Technology
- Rewrite nanosleep() for New Technology
- Polyfill SIGALRM on the New Technology
- select(0,0,0,0) on NT now calls pause()
- Remove some NTDLL calls that aren't needed
- Polyfill SA_NOCLDWAIT on the New Technology
- Polyfill SA_RESETHAND on the New Technology
- Polyfill sigprocmask() on the New Technology
- Polyfill SIGCHLD+SIG_IGN on the New Technology
- Polyfill SA_RESTART masking on the New Technology
- Deliver console signals from main thread on New Technology
- Document SA_RESTART behavior w/ @sarestartable / @norestart
- System call trace in MODE=dbg now prints inherited FDs and signal mask

libc/sock/recvfrom.c

@@ -17,6 +17,7 @@
 │ PERFORMANCE OF THIS SOFTWARE.                                                │
 ╚─────────────────────────────────────────────────────────────────────────────*/
 #include "libc/calls/internal.h"
+#include "libc/calls/strace.internal.h"
 #include "libc/calls/struct/iovec.h"
 #include "libc/dce.h"
 #include "libc/intrin/asan.internal.h"
@@ -40,36 +41,41 @@
  * @error EINTR, EHOSTUNREACH, ECONNRESET (UDP ICMP Port Unreachable),
  *     EPIPE (if MSG_NOSIGNAL), EMSGSIZE, ENOTSOCK, EFAULT, etc.
  * @asyncsignalsafe
+ * @restartable (unless SO_RCVTIMEO)
  */
 ssize_t recvfrom(int fd, void *buf, size_t size, uint32_t flags,
                  void *opt_out_srcaddr, uint32_t *opt_inout_srcaddrsize) {
-  ssize_t got;
+  ssize_t rc, got;
   if (IsAsan() &&
       (!__asan_is_valid(buf, size) ||
        (opt_out_srcaddr &&
         !__asan_is_valid(opt_out_srcaddr, *opt_inout_srcaddrsize)))) {
-    return efault();
-  }
-  if (!IsWindows()) {
+    rc = efault();
+  } else if (IsWindows() && _check_interrupts(false, g_fds.p)) {
+    rc = eintr();
+  } else if (!IsWindows()) {
     got = sys_recvfrom(fd, buf, size, flags, opt_out_srcaddr,
                        opt_inout_srcaddrsize);
     if (opt_out_srcaddr && IsBsd() && got != -1) {
       sockaddr2linux(opt_out_srcaddr);
     }
-    return got;
+    rc = got;
   } else {
     if (__isfdopen(fd)) {
       if (__isfdkind(fd, kFdSocket)) {
-        return sys_recvfrom_nt(&g_fds.p[fd], (struct iovec[]){{buf, size}}, 1,
-                               flags, opt_out_srcaddr, opt_inout_srcaddrsize);
+        rc = sys_recvfrom_nt(&g_fds.p[fd], (struct iovec[]){{buf, size}}, 1,
+                             flags, opt_out_srcaddr, opt_inout_srcaddrsize);
       } else if (__isfdkind(fd, kFdFile) && !opt_out_srcaddr) { /* socketpair */
-        if (flags) return einval();
-        return sys_read_nt(&g_fds.p[fd], (struct iovec[]){{buf, size}}, 1, -1);
+        if (flags) rc = einval();
+        rc = sys_read_nt(&g_fds.p[fd], (struct iovec[]){{buf, size}}, 1, -1);
       } else {
-        return enotsock();
+        rc = enotsock();
       }
     } else {
-      return ebadf();
+      rc = ebadf();
     }
   }
+  STRACE("recvfrom(%d, %#.*hhs, %'zu, %#x) → %'ld% m", fd, size, buf, size,
+         flags, rc);
+  return rc;
 }