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/accept.c

@@ -26,6 +26,7 @@
  * @param inout_addrsize provides and receives addr's byte length
  * @return client fd which needs close(), or -1 w/ errno
  * @asyncsignalsafe
+ * @restartable (unless SO_RCVTIMEO)
  */
 int accept(int fd, void *out_addr, uint32_t *inout_addrsize) {
   return accept4(fd, out_addr, inout_addrsize, 0);

libc/sock/connect.c

@@ -32,6 +32,7 @@
  *
  * @return 0 on success or -1 w/ errno
  * @asyncsignalsafe
+ * @restartable (unless SO_RCVTIMEO)
  */
 int connect(int fd, const void *addr, uint32_t addrsize) {
   int rc;

libc/sock/epoll.c

@@ -1345,7 +1345,7 @@ static textwindows dontinline int sys_epoll_create1_nt(uint32_t flags) {
 }
 
 static textwindows dontinline int sys_epoll_ctl_nt(int epfd, int op, int fd,
-                                                 struct epoll_event *ev) {
+                                                   struct epoll_event *ev) {
   int r;
   struct PortState *port_state;
   struct TsTreeNode *tree_node;
@@ -1375,9 +1375,9 @@ static textwindows dontinline int sys_epoll_ctl_nt(int epfd, int op, int fd,
 }
 
 static textwindows dontinline int sys_epoll_wait_nt(int epfd,
-                                                  struct epoll_event *events,
-                                                  int maxevents,
-                                                  int timeoutms) {
+                                                    struct epoll_event *events,
+                                                    int maxevents,
+                                                    int timeoutms) {
   int num_events;
   struct PortState *port_state;
   struct TsTreeNode *tree_node;
@@ -1493,6 +1493,7 @@ int epoll_ctl(int epfd, int op, int fd, struct epoll_event *ev) {
  * @param maxevents is array length of events
  * @param timeoutms is milliseconds, 0 to not block, or -1 for forever
  * @return number of events stored, 0 on timeout, or -1 w/ errno
+ * @norestart
  */
 int epoll_wait(int epfd, struct epoll_event *events, int maxevents,
                int timeoutms) {

libc/sock/poll-nt.c

@@ -19,6 +19,7 @@
 #include "libc/bits/bits.h"
 #include "libc/bits/weaken.h"
 #include "libc/calls/internal.h"
+#include "libc/calls/sig.internal.h"
 #include "libc/calls/struct/sigaction.h"
 #include "libc/macros.internal.h"
 #include "libc/nt/struct/pollfd.h"
@@ -43,12 +44,8 @@ textwindows int sys_poll_nt(struct pollfd *fds, uint64_t nfds, uint64_t ms) {
     }
   }
   for (;;) {
-    if (cmpxchg(&__interrupted, true, false) ||
-        (weaken(_check_sigchld) && weaken(_check_sigchld)()) ||
-        (weaken(_check_sigwinch) && weaken(_check_sigwinch)(g_fds.p + 0))) {
-      return eintr();
-    }
-    waitfor = MIN(1000, ms); /* for ctrl+c */
+    if (_check_interrupts(false, g_fds.p)) return eintr();
+    waitfor = MIN(__SIG_POLLING_INTERVAL_MS, ms); /* for ctrl+c */
     if ((got = WSAPoll(ntfds, nfds, waitfor)) != -1) {
       if (!got && (ms -= waitfor) > 0) continue;
       for (i = 0; i < nfds; ++i) {

libc/sock/poll.c

@@ -37,6 +37,7 @@
  * @return fds[𝑖].revents flags can have:
  *     (fds[𝑖].events & POLL{IN,OUT,PRI,HUP,ERR,NVAL})
  * @asyncsignalsafe
+ * @norestart
  */
 int poll(struct pollfd *fds, uint64_t nfds, int32_t timeout_ms) {
   int rc;

libc/sock/recv.c

@@ -29,6 +29,7 @@
  * @error EINTR, EHOSTUNREACH, ECONNRESET (UDP ICMP Port Unreachable),
  *     EPIPE (if MSG_NOSIGNAL), EMSGSIZE, ENOTSOCK, EFAULT, etc.
  * @asyncsignalsafe
+ * @restartable (unless SO_RCVTIMEO)
  */
 ssize_t recv(int fd, void *buf, size_t size, int flags) {
   return recvfrom(fd, buf, size, flags, NULL, 0);

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;
 }

libc/sock/recvmsg.c

@@ -36,6 +36,7 @@
  * @error EINTR, EHOSTUNREACH, ECONNRESET (UDP ICMP Port Unreachable),
  *     EPIPE (if MSG_NOSIGNAL), EMSGSIZE, ENOTSOCK, EFAULT, etc.
  * @asyncsignalsafe
+ * @restartable (unless SO_RCVTIMEO)
  */
 ssize_t recvmsg(int fd, struct msghdr *msg, int flags) {
   ssize_t got;

libc/sock/select-nt.c

@@ -17,6 +17,7 @@
 │ PERFORMANCE OF THIS SOFTWARE.                                                │
 ╚─────────────────────────────────────────────────────────────────────────────*/
 #include "libc/bits/popcnt.h"
+#include "libc/calls/calls.h"
 #include "libc/calls/internal.h"
 #include "libc/macros.internal.h"
 #include "libc/mem/mem.h"
@@ -119,12 +120,13 @@ int sys_select_nt(int nfds, fd_set *readfds, fd_set *writefds,
   } else if (timeout) {
     req.tv_sec = timeout->tv_sec;
     req.tv_nsec = timeout->tv_usec * 1000;
-    if ((rc = sys_nanosleep_nt(&req, &rem)) != -1) {
-      timeout->tv_sec = rem.tv_sec;
-      timeout->tv_usec = rem.tv_nsec / 1000;
-    }
+    rem.tv_sec = 0;
+    rem.tv_nsec = 0;
+    rc = sys_nanosleep_nt(&req, &rem);
+    timeout->tv_sec = rem.tv_sec;
+    timeout->tv_usec = rem.tv_nsec / 1000;
   } else {
-    rc = einval();
+    rc = pause();
   }
   return rc;
 }

libc/sock/send.c

@@ -29,6 +29,7 @@
  * @error EINTR, EHOSTUNREACH, ECONNRESET (UDP ICMP Port Unreachable),
  *     EPIPE (if MSG_NOSIGNAL), EMSGSIZE, ENOTSOCK, EFAULT, etc.
  * @asyncsignalsafe
+ * @restartable (unless SO_RCVTIMEO)
  */
 ssize_t send(int fd, const void *buf, size_t size, int flags) {
   return sendto(fd, buf, size, flags, NULL, 0);

libc/sock/sendmsg.c

@@ -36,6 +36,7 @@
  * @error EINTR, EHOSTUNREACH, ECONNRESET (UDP ICMP Port Unreachable),
  *     EPIPE (if MSG_NOSIGNAL), EMSGSIZE, ENOTSOCK, EFAULT, etc.
  * @asyncsignalsafe
+ * @restartable (unless SO_RCVTIMEO)
  */
 ssize_t sendmsg(int fd, const struct msghdr *msg, int flags) {
   if (!IsWindows()) {

libc/sock/sendto.c

@@ -45,6 +45,7 @@
  * @error EINTR, EHOSTUNREACH, ECONNRESET (UDP ICMP Port Unreachable),
  *     EPIPE (if MSG_NOSIGNAL), EMSGSIZE, ENOTSOCK, EFAULT, etc.
  * @asyncsignalsafe
+ * @restartable (unless SO_RCVTIMEO)
  */
 ssize_t sendto(int fd, const void *buf, size_t size, uint32_t flags,
                const void *opt_addr, uint32_t addrsize) {