Make improvements

- Improved async signal safety of read() particularly for longjmp()
- Started adding cancel cleanup handlers for locks / etc on Windows
- Make /dev/tty work better particularly for uses like `foo | less`
- Eagerly read console input into a linked list, so poll can signal
- Fix some libc definitional bugs, which configure scripts detected

libc/intrin/describefdset.c

@@ -0,0 +1,61 @@
+/*-*- 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 2021 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/dce.h"
+#include "libc/intrin/asan.internal.h"
+#include "libc/intrin/bsr.h"
+#include "libc/intrin/kprintf.h"
+#include "libc/sock/select.h"
+#include "libc/sock/select.internal.h"
+
+#define N 100
+
+#define append(...) o += ksnprintf(buf + o, N - o, __VA_ARGS__)
+
+const char *(DescribeFdSet)(char buf[N], ssize_t rc, int nfds, fd_set *fds) {
+  int o = 0;
+
+  if (!fds) return "NULL";
+  if ((!IsAsan() && kisdangerous(fds)) ||
+      (IsAsan() && !__asan_is_valid(fds, sizeof(*fds) * nfds))) {
+    ksnprintf(buf, N, "%p", fds);
+    return buf;
+  }
+
+  append("{");
+
+  bool gotsome = false;
+  for (int fd = 0; fd < nfds; fd += 64) {
+    uint64_t w = fds->fds_bits[fd >> 6];
+    while (w) {
+      unsigned o = _bsr(w);
+      w &= ~((uint64_t)1 << o);
+      if (fd + o < nfds) {
+        if (!gotsome) {
+          gotsome = true;
+          append(", ");
+          append("%d", fd);
+        }
+      }
+    }
+  }
+
+  append("}");
+
+  return buf;
+}