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Non syscall's wrappers but something like snprintf(), dprintf()
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An async-signal-safe function is one that can be safely called from within a signal handler. Many functions are not async- signal-safe. In particular, nonreentrant functions are generally unsafe to call from a signal handler.
The sprintf() and snprintf() functions are Async-Signal-Safe. The printf() and fprintf() functions can be used safely in multithreaded applications, as long as setlocale(3C) is not being called to change the locale.
Your process will deadlock inside the signal handler, because malloc will be unable to acquire the heap lock. Your process will corrupt its heap, because malloc does acquire the lock (or doesn't think it needs it), then proceeds to render the heap inconsistent, leading to a later crash.
The signal() function does not (necessarily) block other signals from arriving while the current handler is executing; sigaction() can block other signals until the current handler returns. The signal() function (usually) resets the signal action back to SIG_DFL (default) for almost all signals.
I am pretty sure you have to see the documentation
Edit: How about this list then?
From man signal:
NOTES
The effects of this call in a multi-threaded process are unspecified.
The routine handler must be very careful, since processing elsewhere
was interrupted at some arbitrary point. POSIX has the concept of "safe
function". If a signal interrupts an unsafe function, and handler
calls an unsafe function, then the behavior is undefined. Safe func-
tions are listed explicitly in the various standards. The POSIX.1-2003
list is
_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() fdata-
sync() fork() fpathconf() fstat() fsync() ftruncate() getegid()
geteuid() getgid() getgroups() getpeername() getpgrp() getpid() getp-
pid() 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() sig-
fillset() sigismember() signal() sigpause() sigpending() sigprocmask()
sigqueue() sigset() sigsuspend() sleep() socket() socketpair() stat()
symlink() sysconf() tcdrain() tcflow() tcflush() tcgetattr() tcgetp-
grp() tcsendbreak() tcsetattr() tcsetpgrp() time() timer_getoverrun()
timer_gettime() timer_settime() times() umask() uname() unlink()
utime() wait() waitpid() write().
According to POSIX, the behaviour of a process is undefined after it
ignores a SIGFPE, SIGILL, or SIGSEGV signal that was not generated by
the kill(2) or the raise(3) functions. Integer division by zero has
undefined result. On some architectures it will generate a SIGFPE sig-
nal. (Also dividing the most negative integer by -1 may generate
SIGFPE.) Ignoring this signal might lead to an endless loop.
See sigaction(2) for details on what happens when SIGCHLD is set to
SIG_IGN.
The use of sighandler_t is a GNU extension. Various versions of libc
predefine this type; libc4 and libc5 define SignalHandler, glibc
defines sig_t and, when _GNU_SOURCE is defined, also sighandler_t.
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