unixsig.c File Reference

#include <stdio.h>
#include <signal.h>
#include <stdatomic.h>
#include "internal.h"

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Functions
int	block_signals (sigset_t *old_blocked_signals)
int	unblock_signals (const sigset_t *old_blocked_signals)
int	drop_signals (void *nc, void **altstack)
void	setup_alt_sig_stack (void)
int	setup_signals (void *vnc, bool no_quit_sigs, bool no_winch_sigs, int(*handler)(void *, void **, int))

Function Documentation

block_signals()

int block_signals

(

sigset_t *

old_blocked_signals

)

Definition at line 82 of file unixsig.c.

                                                {
  if(pthread_sigmask(SIG_BLOCK, &wblock_signals, old_blocked_signals)){
    return -1;
  }
  return 0;
}

drop_signals()

int drop_signals	(	void *	nc,
		void **	altstack
	)

Definition at line 104 of file unixsig.c.

                                           {
  int ret = -1;
  void* expected = nc;
  if(!altstack){ // came in via signal handler
    return 0;
  }
  *altstack = NULL;
  pthread_mutex_lock(&lock);
  if(atomic_compare_exchange_strong(&signal_nc, &expected, nc)){
    if(handling_winch){
      sigaction(SIGWINCH, &old_winch, NULL);
      sigaction(SIGCONT, &old_cont, NULL);
      handling_winch = false;
    }
    if(handling_fatals){
      sigaction(SIGABRT, &old_abrt, NULL);
      sigaction(SIGBUS, &old_bus, NULL);
      sigaction(SIGFPE, &old_fpe, NULL);
      sigaction(SIGILL, &old_ill, NULL);
      sigaction(SIGINT, &old_int, NULL);
      sigaction(SIGQUIT, &old_quit, NULL);
      sigaction(SIGSEGV, &old_segv, NULL);
      sigaction(SIGTERM, &old_term, NULL);
      handling_fatals = false;
    }
    if(alt_signal_stack.ss_sp){
      alt_signal_stack.ss_flags = SS_DISABLE;
      if(sigaltstack(&alt_signal_stack, NULL)){
        if(errno != EPERM){
          fprintf(stderr, "couldn't remove alternate signal stack (%s)", strerror(errno));
        }
      }
    }
    *altstack = alt_signal_stack.ss_sp;
    alt_signal_stack.ss_sp = NULL;
    ret = !atomic_compare_exchange_strong(&signal_nc, &expected, NULL);
  }
  pthread_mutex_unlock(&lock);
  if(ret){
    fprintf(stderr, "signals weren't registered for %p (had %p)", nc, expected);
  }
  // we might not have established any handlers in setup_signals(); always
  // return 0 here, for now...
  return 0;
}

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setup_alt_sig_stack()

void setup_alt_sig_stack

(

void

)

Definition at line 182 of file unixsig.c.

                              {
  pthread_mutex_lock(&lock);
  if(alt_signal_stack.ss_sp){
    if(sigaltstack(&alt_signal_stack, NULL)){
      logerror("error installing alternate signal stack (%s)", strerror(errno));
    }
  }
  pthread_mutex_unlock(&lock);
}

setup_signals()

int setup_signals	(	void *	vnc,
		bool	no_quit_sigs,
		bool	no_winch_sigs,
		int(*)(void *, void **, int)	handler
	)

Definition at line 195 of file unixsig.c.

                                                    {
  notcurses* nc = vnc;
  void* expected = NULL;
  struct sigaction sa;
  // don't register ourselves if we don't intend to set up signal handlers
  // we expect NULL (nothing registered), and want to register nc
  if(!atomic_compare_exchange_strong(&signal_nc, &expected, nc)){
    fprintf(stderr, "%p is already registered for signals (provided %p)" NL, expected, nc);
    return -1;
  }
  pthread_mutex_lock(&lock);
  if(!no_winch_sigs){
    memset(&sa, 0, sizeof(sa));
    sa.sa_handler = sigwinch_handler;
    sigaddset(&sa.sa_mask, SIGWINCH);
    sigaddset(&sa.sa_mask, SIGCONT);
    int ret = 0;
    ret |= sigaction(SIGWINCH, &sa, &old_winch);
    ret |= sigaction(SIGCONT, &sa, &old_cont);
    if(ret){
      atomic_store(&signal_nc, NULL);
      pthread_mutex_unlock(&lock);
      fprintf(stderr, "error installing term signal handler (%s)" NL, strerror(errno));
      return -1;
    }
    // we're not going to be restoring the old mask at exit, as who knows,
    // they might have masked more things afterwards.
    pthread_sigmask(SIG_BLOCK, &sa.sa_mask, NULL);
    handling_winch = true;
  }
  if(!no_quit_sigs){
    memset(&sa, 0, sizeof(sa));
// AddressSanitizer doesn't want us to use sigaltstack(). we could force everyone
// to export ASAN_OPTIONS=use_sigaltstack=0, or just not fuck with the alternate
// signal stack when built with ASAN.
#ifndef USE_ASAN
#ifdef _SC_SIGSTKSZ
    long minstksz = sysconf(_SC_SIGSTKSZ);
#else
    long minstksz = 0;
#endif
    if(minstksz <= 0){
      minstksz = SIGSTKSZ * 4;
    }
    alt_signal_stack.ss_sp = malloc(minstksz);
    if(alt_signal_stack.ss_sp == NULL){
      fprintf(stderr, "warning: couldn't create %ldB alternate signal stack (%s)" NL, minstksz, strerror(errno));
    }else{
      alt_signal_stack.ss_size = minstksz;
      if(sigaltstack(&alt_signal_stack, NULL)){
        fprintf(stderr, "warning: couldn't set up %ldB alternate signal stack (%s)" NL, minstksz, strerror(errno));
        free(alt_signal_stack.ss_sp);
        alt_signal_stack.ss_sp = NULL;
        alt_signal_stack.ss_size = 0;
      }else{
        sa.sa_flags = SA_ONSTACK;
      }
    }
#endif
    fatal_callback = handler;
    sa.sa_sigaction = fatal_handler;
    sigaddset(&sa.sa_mask, SIGABRT);
    sigaddset(&sa.sa_mask, SIGBUS);
    sigaddset(&sa.sa_mask, SIGFPE);
    sigaddset(&sa.sa_mask, SIGILL);
    sigaddset(&sa.sa_mask, SIGINT);
    sigaddset(&sa.sa_mask, SIGQUIT);
    sigaddset(&sa.sa_mask, SIGSEGV);
    sigaddset(&sa.sa_mask, SIGTERM);
    // don't try to handle fatal signals twice, and use our alternative stack
    sa.sa_flags |= SA_SIGINFO | SA_RESETHAND;
    int ret = 0;
    ret |= sigaction(SIGABRT, &sa, &old_abrt);
    ret |= sigaction(SIGBUS, &sa, &old_bus);
    ret |= sigaction(SIGFPE, &sa, &old_fpe);
    ret |= sigaction(SIGILL, &sa, &old_ill);
    ret |= sigaction(SIGINT, &sa, &old_int);
    ret |= sigaction(SIGQUIT, &sa, &old_quit);
    ret |= sigaction(SIGSEGV, &sa, &old_segv);
    ret |= sigaction(SIGTERM, &sa, &old_term);
    if(ret){
      atomic_store(&signal_nc, NULL);
      pthread_mutex_unlock(&lock);
      fprintf(stderr, "error installing fatal signal handlers (%s)" NL, strerror(errno));
      return -1;
    }
    handling_fatals = true;
  }
  // we don't really want to go blocking SIGSEGV etc while we write, but
  // we *do* temporarily block user-initiated signals.
  sigaddset(&wblock_signals, SIGINT);
  sigaddset(&wblock_signals, SIGTERM);
  sigaddset(&wblock_signals, SIGQUIT);
  pthread_mutex_unlock(&lock);
  return 0;
}

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unblock_signals()

int unblock_signals

(

const sigset_t *

old_blocked_signals

)

Definition at line 89 of file unixsig.c.

                                                        {
  if(pthread_sigmask(SIG_SETMASK, old_blocked_signals, NULL)){
    return -1;
  }
  return 0;
}