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SubjectRE: Dumb question: Why are exceptions such as SIGSEGV not logged
Date

> On 19 August 2003 01:39, David Schwartz wrote:

> > > And why not just catch the ones sent from the kernel? That's
> > > the one that
> > > is killing the program because it crashed, and that's the one the
> > > origional
> > > poster wants logged...

> > Because sometimes a program wants to terminate. And it is
> > perfectly legal
> > for a programmer who needs to terminate his program as quickly
> > as possible
> > to do this:
> >
> > char *j=NULL;
> > signal(SIGSEGV, SIG_DFL);
> > *j++;

> > This is a perfectly sensible thing for a program to do with
> > well-defined
> > semantics. If a program wants to create a child every minute
> > like this and
> > kill it, that's perfectly fine. We should be able to do that in
> > the default
> > configuration without a sysadmin complaining that we're DoSing
> > his syslogs.

> I disagree. _exit(2) is the most sensible way to terminate.

Read the documentation for _exit. You will see that it is useless in the
case of a portable program that needs to terminate as quickly as possible
and, in fact, isn't guaranteed to cause program termination at all:

The function _exit is like exit(), but does not call any
functions registered with the ANSI C atexit function, nor
any registered signal handlers. Whether it flushes stan-
dard I/O buffers and removes temporary files created with
tmpfile(3) is implementation-dependent. On the other
hand, _exit does close open file descriptors, and this may
cause an unknown delay, waiting for pending output to fin-
ish. If the delay is undesired, it may be useful to call
functions like tcflush() before calling _exit(). Whether
any pending I/O is cancelled, and which pending I/O may be
cancelled upon _exit(), is implementation-dependent.

One major problem with _exit() is that it touches various structures. If
the program's execution environment is no longer trusted, calling _exit()
can cause an endless loop. In multithreaded programs, _exit() may need to
acquire mutexes. This can take an indeterminate amount of time. Portable
programs cannot rely on _exit() in a case where they need to terminate as
soon as possible.

Now, if you have a better way for a portable program that needs to
terminate immediately to do so, that's fine, tell me what it is. Otherwise,
you are *forcing* people to DoS your syslog.

DS


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