Fix bugs and make improvements

- Get clone() working on FreeBSD
- Increase some Python build quotas
- Add more atomic builtins to chibicc
- Fix ASAN poisoning of alloca() memory
- Make MODE= mandatory link path tinier
- Improve the examples folder a little bit
- Start working on some more resource limits
- Make the linenoise auto-complete UI as good as GNU readline
- Update compile.com, avoiding AVX codegen on non-AVX systems
- Make sure empty path to syscalls like opendir raises ENOENT
- Correctly polyfill ENOENT vs. ENOTDIR on the New Technology
- Port bestline's paredit features to //third_party/linenoise
- Remove workarounds for RHEL 5.0 bugs that were fixed in 5.1

examples/crashreport2.c

@@ -0,0 +1,52 @@
+#if 0
+/*─────────────────────────────────────────────────────────────────╗
+│ To the extent possible under law, Justine Tunney has waived      │
+│ all copyright and related or neighboring rights to this file,    │
+│ as it is written in the following disclaimers:                   │
+│   • http://unlicense.org/                                        │
+│   • http://creativecommons.org/publicdomain/zero/1.0/            │
+╚─────────────────────────────────────────────────────────────────*/
+#endif
+#include "libc/calls/calls.h"
+#include "libc/log/log.h"
+#include "libc/stdio/stdio.h"
+
+/**
+ * @fileoverview CTRL+\ debugging example
+ *
+ *     make -j8 -O o//examples/crashreport2.com
+ *     o//examples/crashreport2.com
+ *
+ * Assuming you call ShowCrashReports() from main(), you can press
+ * `CTRL+\` at anny time to generate a `SIGQUIT` message that lets you
+ * debug wrongness and freezups.
+ *
+ * On supported platforms, this will cause GDB to automatically attach.
+ * The nice thing about this, is you can start stepping through your
+ * code at the precice instruction where the interrupt happened. See
+ * `libc/log/attachdebugger.c` to see how it works.
+ *
+ * If you wish to suppress the auto-GDB behavior, then:
+ *
+ *     export GDB=
+ *
+ * Or alternatively:
+ *
+ *    extern int __isworker;
+ *    __isworker = true;
+ *
+ * Will cause your `SIGQUIT` handler to just print a crash report
+ * instead. This is useful for production software that might be running
+ * in a terminal environment like GNU Screen, but it's not desirable to
+ * have ten worker processes trying to attach GDB at once.
+ */
+
+int main(int argc, char *argv[]) {
+  volatile int64_t x;
+  ShowCrashReports();
+  printf("please press ctrl+\\ and see what happens...\n");
+  sigsuspend(0);
+  printf("\n\n");
+  printf("congratulations! your program is now resuming\n");
+  return 0;
+}

examples/hangman.c

@@ -44,8 +44,8 @@
 #include "libc/str/str.h"
 #include "libc/time/time.h"
 #include "third_party/zlib/zlib.h"
+// clang-format off
 
-/* clang-format off */
 #define DICT "usr/share/dict/hangman"
 #define MAXERR 7
 #define MINSCORE 0

examples/rlimit.c

@@ -0,0 +1,72 @@
+#if 0
+/*─────────────────────────────────────────────────────────────────╗
+│ To the extent possible under law, Justine Tunney has waived      │
+│ all copyright and related or neighboring rights to this file,    │
+│ as it is written in the following disclaimers:                   │
+│   • http://unlicense.org/                                        │
+│   • http://creativecommons.org/publicdomain/zero/1.0/            │
+╚─────────────────────────────────────────────────────────────────*/
+#endif
+#include "libc/calls/calls.h"
+#include "libc/calls/strace.internal.h"
+#include "libc/calls/struct/rlimit.h"
+#include "libc/errno.h"
+#include "libc/intrin/kprintf.h"
+#include "libc/log/color.internal.h"
+#include "libc/macros.internal.h"
+#include "libc/stdio/stdio.h"
+#include "libc/str/str.h"
+#include "libc/sysv/consts/rlim.h"
+#include "libc/sysv/consts/rlimit.h"
+
+/**
+ * @fileoverview tool for printing and changing system resource limits
+ *
+ * This is what you do if you want to not accidentally bomb your system
+ * with runaway code. If you haven't accidentally bombed your UNIX
+ * system before then you're not pushing it hard enough.
+ */
+
+static void SetLimit(int resource, uint64_t soft, uint64_t hard) {
+  struct rlimit old;
+  struct rlimit lim = {soft, hard};
+  if (resource == 127) return;
+  if (setrlimit(resource, &lim) == -1) {
+    if (!getrlimit(resource, &old)) {
+      lim.rlim_max = MIN(hard, old.rlim_max);
+      lim.rlim_cur = MIN(soft, lim.rlim_max);
+      if (!setrlimit(resource, &lim)) {
+        fprintf(stderr, "%snote: setrlimit(%s) downgraded to {%,ld, %,ld}\n",
+                __strace_rlimit_name(resource), lim.rlim_cur, lim.rlim_max);
+        return;
+      }
+    }
+    fprintf(stderr, "error: setrlimit(%s, %,ld, %,ld) failed %m%n",
+            __strace_rlimit_name(resource), soft, hard);
+    exit(1);
+  }
+}
+
+int main(int argc, char *argv[]) {
+  int i, rc;
+  struct rlimit rlim;
+
+  // // example of how you might change the limits
+  // SetLimit(RLIMIT_CPU, 3, 33);
+  // SetLimit(RLIMIT_NPROC, 4, 128);
+  // SetLimit(RLIMIT_NOFILE, 32, 128);
+  // SetLimit(RLIMIT_SIGPENDING, 16, 1024);
+  // SetLimit(RLIMIT_AS, 8 * 1024 * 1024, 1l * 1024 * 1024 * 1024);
+  // SetLimit(RLIMIT_RSS, 8 * 1024 * 1024, 1l * 1024 * 1024 * 1024);
+  // SetLimit(RLIMIT_DATA, 8 * 1024 * 1024, 1l * 1024 * 1024 * 1024);
+  // SetLimit(RLIMIT_FSIZE, 8 * 1000 * 1000, 1l * 1000 * 1000 * 1000);
+
+  for (i = 0; i < RLIM_NLIMITS; ++i) {
+    rc = getrlimit(i, &rlim);
+    printf("setrlimit(%-20s, %,16ld, %,16ld) → %d %s\n",
+           __strace_rlimit_name(i), rlim.rlim_cur, rlim.rlim_max, rc,
+           !rc ? "" : strerror(errno));
+  }
+
+  return 0;
+}

examples/ucontext-sigfpe-recovery.c

@@ -16,12 +16,22 @@
 #include "libc/sysv/consts/sig.h"
 #include "third_party/xed/x86.h"
 
+/**
+ * @fileoverview How to change CPU state on signal delivery
+ *
+ * This program redefines division by zero so that it has a definition.
+ * The definition is the meaning of life, the universe, and everything.
+ * Normally crash signals like `SIGSEGV`, `SIGILL`, and `SIGFPE` aren't
+ * recoverable. This example shows how it actually can be done with Xed
+ * and this example should work on all supported platforms even Windows
+ */
+
 void handler(int sig, siginfo_t *si, ucontext_t *ctx) {
   struct XedDecodedInst xedd;
   xed_decoded_inst_zero_set_mode(&xedd, XED_MACHINE_MODE_LONG_64);
   xed_instruction_length_decode(&xedd, (void *)ctx->uc_mcontext.rip, 15);
   ctx->uc_mcontext.rip += xedd.length;
-  ctx->uc_mcontext.rax = 42;
+  ctx->uc_mcontext.rax = 42;  // set the DIV result registers rdx:rax
   ctx->uc_mcontext.rdx = 0;
 }