SEI CERT C Coding Standard

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The _Exit() function called from within the int_handler() signal handler causes immediate program termination, and is async-safe, whereas exit() may call cleanup routines first, and is consequently not async-safe.

Implementation Details

OpenBSD

The OpenBSD signal() man page identifies functions that are asynchronous-signal safe. Applications may consequently invoke them, without restriction, from signal-catching functions.

POSIX

Wiki Markup
The following table from the the Open Group Base Specifications \[[Open Group 04|AA. C References#Open Group 04]\] defines a set of functions that are either reentrant or non-interruptible by signals and are async-signal-safe. Applications may consequently invoke them, without restriction, from signal-catching functions:

_Exit()

_exit()

abort()

accept()

access()

aio_error()

aio_return()

aio_suspend()

alarm()

bind()

cfgetispeed()

cfgetospeed()

cfsetispeed()

cfsetospeed()

chdir()

chmod()

chown()

clock_gettime()

close()

connect()

creat()

dup()

dup2()

execle()

execve()

fchmod()

fchown()

fcntl()

fdatasync()

fork()

fpathconf()

fstat()

fsync()

ftruncate()

getegid()

geteuid()

getgid()

getgroups()

getpeername()

getpgrp()

getpid()

getppid()

getsockname()

getsockopt()

getuid()

kill()

link()

listen()

lseek()

lstat()

mkdir()

mkfifo()

open()

pathconf()

pause()

pipe()

poll()

posix_trace_event()

pselect()

raise()

read()

readlink()

recv()

recvfrom()

recvmsg()

rename()

rmdir()

select()

sem_post()

send()

sendmsg()

sendto()

setgid()

setpgid()

setsid()

setsockopt()

setuid()

shutdown()

sigaction()

sigaddset()

sigdelset()

sigemptyset()

sigfillset()

sigismember()

sleep()

signal()

sigpause()

sigpending()

sigprocmask()

sigqueue()

sigset()

sigsuspend()

sockatmark()

socket()

socketpair()

stat()

symlink()

sysconf()

tcdrain()

tcflow()

tcflush()

tcgetattr()

tcgetpgrp()

tcsendbreak()

tcsetattr()

tcsetpgrp()

time()

timer_getoverrun()

timer_gettime()

timer_settime()

times()

umask()

uname()

unlink()

utime()

wait()

waitpid()

write()

 

 

All functions not in the above table are considered to be unsafe with respect to signals. In the presence of signals, all functions defined by this volume of IEEE Std 1003.1-2001 shall behave as defined when called from or interrupted by a signal-catching function, with a single exception: when a signal interrupts an unsafe function and the signal-catching function calls an unsafe function, the behavior is undefined.

Compliant Solution

Signal handlers should be as concise as possible, ideally unconditionally setting a flag and returning. They may also call the _Exit() function.

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