text: /*-*- 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/calls/calls.h"
  #include "libc/calls/struct/sigaction.h"
  #include "libc/calls/struct/sigaltstack.h"
  #include "libc/log/internal.h"
  #include "libc/log/log.h"
  #include "libc/macros.internal.h"
  #include "libc/runtime/stack.h"
  #include "libc/runtime/symbols.internal.h"
  #include "libc/sysv/consts/map.h"
  #include "libc/sysv/consts/prot.h"
  #include "libc/sysv/consts/sa.h"
  #include "libc/sysv/consts/sig.h"
  #include "libc/sysv/consts/ss.h"
  
  STATIC_YOINK("__die");                /* for backtracing */
  STATIC_YOINK("malloc_inspect_all");   /* for asan memory origin */
  STATIC_YOINK("__get_symbol_by_addr"); /* for asan memory origin */
  
  extern const unsigned char __oncrash_thunks[8][11];
  static struct sigaltstack g_oldsigaltstack;
  static struct sigaction g_oldcrashacts[7];
  
  static void InstallCrashHandlers(int extraflags) {
    size_t i;
    struct sigaction sa;
    bzero(&sa, sizeof(sa));
    sa.sa_flags = SA_SIGINFO | SA_NODEFER | extraflags;
    sigfillset(&sa.sa_mask);
    for (i = 0; i < ARRAYLEN(kCrashSigs); ++i) {
      sigdelset(&sa.sa_mask, kCrashSigs[i]);
    }
    for (i = 0; i < ARRAYLEN(kCrashSigs); ++i) {
      if (kCrashSigs[i]) {
        sa.sa_sigaction = (sigaction_f)__oncrash_thunks[i];
        sigaction(kCrashSigs[i], &sa, &g_oldcrashacts[i]);
      }
    }
  }
  
  relegated void RestoreDefaultCrashSignalHandlers(void) {
    size_t i;
    sigset_t ss;
    sigemptyset(&ss);
    sigprocmask(SIG_SETMASK, &ss, NULL);
    for (i = 0; i < ARRAYLEN(kCrashSigs); ++i) {
      if (kCrashSigs[i]) {
        sigaction(kCrashSigs[i], &g_oldcrashacts[i], NULL);
      }
    }
  }
  
  static void FreeSigAltStack(void *p) {
    InstallCrashHandlers(0);
    sigaltstack(&g_oldsigaltstack, 0);
    munmap(p, GetStackSize());
  }
  
  /**
   * Installs crash signal handlers.
   *
   * Normally, only functions calling die() will print backtraces. This
   * function may be called at program startup to install handlers that
   * will display similar information, for most types of crashes.
   *
   *   - Backtraces
   *   - CPU state printout
   *   - Automatic debugger attachment
   *
   * Another trick this function enables, is you can press CTRL+\ to open
   * the debugger GUI at any point while the program is running. It can be
   * useful, for example, if a program is caught in an infinite loop.
   *
   * @see callexitontermination()
   */
  void ShowCrashReports(void) {
    char *sp;
    struct sigaltstack ss;
    /* <SYNC-LIST>: showcrashreports.c, oncrashthunks.S, oncrash.c */
    kCrashSigs[0] = SIGQUIT; /* ctrl+\ aka ctrl+break */
    kCrashSigs[1] = SIGFPE;  /* 1 / 0 */
    kCrashSigs[2] = SIGILL;  /* illegal instruction */
    kCrashSigs[3] = SIGSEGV; /* bad memory access */
    kCrashSigs[4] = SIGTRAP; /* bad system call */
    kCrashSigs[5] = SIGABRT; /* abort() called */
    kCrashSigs[6] = SIGBUS;  /* misaligned, noncanonical ptr, etc. */
    /* </SYNC-LIST>: showcrashreports.c, oncrashthunks.S, oncrash.c */
    if (!IsWindows()) {
      bzero(&ss, sizeof(ss));
      ss.ss_flags = 0;
      ss.ss_size = GetStackSize();
      // FreeBSD sigaltstack() will EFAULT if we use MAP_STACK here
      // OpenBSD sigaltstack() auto-applies MAP_STACK to the memory
      if ((sp = mmap(0, GetStackSize(), PROT_READ | PROT_WRITE,
                     MAP_PRIVATE | MAP_ANONYMOUS, -1, 0)) != MAP_FAILED) {
        ss.ss_sp = sp;
        if (!sigaltstack(&ss, &g_oldsigaltstack)) {
          __cxa_atexit(FreeSigAltStack, ss.ss_sp, 0);
        } else {
          munmap(ss.ss_sp, GetStackSize());
        }
      }
      InstallCrashHandlers(SA_ONSTACK);
    } else {
      InstallCrashHandlers(0);
    }
    GetSymbolTable();
  }
  