Hi what's the reason for having the default disposition for SIGSEGV,
SIGFPE, SIGBUS etc to be terminating the program, when these signals can
just be ignored by the program? Many programs crash with SIGSEGV -
they'd be much less flakey if the default was to try to carry on.
~Jon~
Nov 2 '07
29  2111 
In article <11************ **********@19g2 000hsx.googlegr oups.com>, ja*********@ver izon.net wrote:
Leet Jon wrote:
On 2 Nov 2007 at 19:10, Keith Thompson wrote:
However, letting a program continue running by default after a
catastrophic data-corrupting failure would not be a good idea. If a
program dies immediately after "an invalid access to storage" (which
is all the C standard says about SIGSEGV), then you have a good chance
of diagnosing and correcting the problem before putting the code into
production. If the error is ignored, the program will very likely
continue to corrupt your data in subtle ways; tracking it down and
fixing it is going to be difficult if the error occurs at a customer
site, or even during an important demo.
I believe you are completely wrong on this point. Very often a SIGSEGV
will be caused by (say) a single bad array access - the consequences
will be highly localized, and carrying on with the program will not
cause any significant problems.
In general, if that bad array access is a write, it may completely
mess up some other part of the program.
If the write gets a SIGSEGV, it doesn't actually write anything. The
meaning of that signal is that you tried to write to a nonexistent
virtual address. So if by "mess up some other part of the program" you
meant that it would overwrite that part's data, that obviously can't
happen.
On the other hand, if some other part of the program was expecting to
read what you wrote, it will certainly be messed up by the lack of that
data.
Who wants their customer to run their program and have it just crash
with a segfault?
Given the choice between crashing, and continuing to run, I strongly
prefer the crash. If someone desperately needs that program to be
running, they presumably need it to run correctly, and that's highly
unlikely after an ignored SIGSEG signal.
Agreed. Almost any time a program gets one of these signals, it means
it has a serious bug. It's better to find out that it's broken than to
pretend it isn't.
--
Barry Margolin, ba****@alum.mit .edu
Arlington, MA
*** PLEASE post questions in newsgroups, not directly to me ***
*** PLEASE don't copy me on replies, I'll read them in the group ***
Leet Jon wrote:
I believe you are completely wrong on this point. Very often a SIGSEGV
will be caused by (say) a single bad array access - the consequences
will be highly localized, and carrying on with the program will not
cause any significant problems.
And very often this will not be the case and quitting before more damage
happens is the best thing.
For example, consider a program which moves a tree of files from one
filesystem to another by copying them and then deleting the originals
once the copy finishes successfully. And suppose you get a SIGSEGV
while building the list of files to copy. If you ignore it, you might
end up making copies of half the files, then deleting all the originals!
If you really want to recover from local faults, then use a language that
does bounds checking on arrays and pointer/reference dereferencing and
throws exceptions when these things happen. Then if you know such
errors really won't corrupt the state of the larger program and that the
fault is really localized, you can write an exception handler to do the
error recovery and contain the fault within whatever bounds you've
pre-determined it actually *can* be confined within.
Who wants their customer to run their program and have it just crash
with a segfault?
I'd much rather the customer encounter a segfault, file a bug report,
and give me a chance to fix it than I would have it just silently fail
and let the error continue, corrupting data or whatever else for who
knows how many years upon years. There was a trend in business a
decade or two ago called "total quality management" (or TQM), and the
basic idea was that when faults happen, you should not whitewash over
them, and you should instead stop what you're doing and not proceed
until you've corrected the problem. This was carried a little too far
(like most trendy business ideas), but there is some merit to this
approach. Ignoring failures just (a) causes problems and (b) encourages
people to stop caring about whether they cause failures.
- lOGAN
Leet Jon <jo*@nospam.com writes:
On 2 Nov 2007 at 19:10, Keith Thompson wrote:
>However, letting a program continue running by default after a
catastrophic data-corrupting failure would not be a good idea. If a
program dies immediately after "an invalid access to storage" (which
is all the C standard says about SIGSEGV), then you have a good chance
of diagnosing and correcting the problem before putting the code into
production. If the error is ignored, the program will very likely
continue to corrupt your data in subtle ways; tracking it down and
fixing it is going to be difficult if the error occurs at a customer
site, or even during an important demo.
I believe you are completely wrong on this point. Very often a SIGSEGV
will be caused by (say) a single bad array access - the consequences
will be highly localized, and carrying on with the program will not
cause any significant problems.
Who wants their customer to run their program and have it just crash
with a segfault? That hardly comes across as professional. Better to try
your best to carry on and weather the storm than to just dump the user
with a crash.
I can understand that for debugging purposes you might want to have
SIGSEGV etc. generate a core file, but in production code the default
should be for these signals to be ignored.
Let me paraphrase this ('my' is here supposed to mean 'Leet Jon'):
My code is full of ocasionally happening invalid memory accesses,
which I am to lazy to debug, even if I could. But my customers have no
way if knowing this, except, unfortunately, these invalid memory
accesses lead to the kernel terminating the process. Since they cannot
possibly tell if some output of the program has been generated in the
course of the algoritms they think it would be performing on the data
they fed to it, has instead been calculated using left-over register
contents from arbitrary functions, which could not be replaced because
of faulting load instructions and intermediate results having
vanished into nowhere land because the stores intended to store them
faulted, too, not taking into account that the control flow has
been mostly unpredictable due to corrupted stack frames, they would
just happily accpet it. I am convinced it works most of the time.
Now, for the sake of the argument, let's swap 'program' with 'electric
device', invalid memory access with 'improperly isolated flow of
current' and 'works most of time' with 'only kills someone every now
and then'.
Except for 'traditional lenience' wrt to software, there is no
'functional' difference.
On 2 Nov 2007 at 20:34, Al Balmer wrote:
>>I can understand that for debugging purposes you might want to have
SIGSEGV etc. generate a core file, but in production code the default
should be for these signals to be ignored.
In production code, those signals should never be generated. If they
are, they should crash, so that the user can complain, and someone can
fix it.
Perhaps you are unaware that some C code is run in safety-critical
environments - having a program that dumps core at the drop of a hat
rather than carrying on running could literally be the difference
between life and death. OK, so *maybe* the error condition causing the
SIGSEGV will propagate and bring the program down later, but taking that
chance is a better option than immediately failing.
~Jon~
"Leet Jon" <jo*@nospam.com schrieb im Newsbeitrag
news:sl******** ***********@nos pam.com...
On 2 Nov 2007 at 20:34, Al Balmer wrote:
>>>I can understand that for debugging purposes you might want to have
SIGSEGV etc. generate a core file, but in production code the default
should be for these signals to be ignored.
In production code, those signals should never be generated. If they
are, they should crash, so that the user can complain, and someone can
fix it.
Perhaps you are unaware that some C code is run in safety-critical
environments - having a program that dumps core at the drop of a hat
rather than carrying on running could literally be the difference
between life and death. OK, so *maybe* the error condition causing the
SIGSEGV will propagate and bring the program down later, but taking that
chance is a better option than immediately failing.
I beg your pardon? A program in a safety-critical environment should be
tested properly so that SIGSEGVs simply don't happen.
Als I'd rather have the program crash and a human operator take over control
Exapmple a flight auto pilot, program gets a SIGSEV but continues without
telling anybody and the plane crashes into a mountain as a result of it's
wrong calculations. Alternative: The progam abends, The system tells the
pilot about it and the pilot takes over control.
Bye, Jojo
Leet Jon wrote:
On 2 Nov 2007 at 20:34, Al Balmer wrote:
>>I can understand that for debugging purposes you might want to have
SIGSEGV etc. generate a core file, but in production code the default
should be for these signals to be ignored.
In production code, those signals should never be generated. If they
are, they should crash, so that the user can complain, and someone can
fix it.
Perhaps you are unaware that some C code is run in safety-critical
environments - having a program that dumps core at the drop of a hat
rather than carrying on running could literally be the difference
between life and death.
In safety-critical systems, you don't want to depend on a module in an
undefined state. In a fault-tolerant design, you avoid depending on
single point of failure modules.
How are you supposed to detect a HW fault in time, if ignoring
signals/exceptions?
The way this usually works, is that faults are not ignored, but when
detected, the module is taken down by a monitor program, some error
recovery can be performed by restarting the module, if that fails, the
module is shut down for good.
The system continue working, by resuming processing in independent HW,
from a well-defined state.
OK, so *maybe* the error condition causing the
SIGSEGV will propagate and bring the program down later, but taking that
chance is a better option than immediately failing.
Hopefully, you are not programming a nuclear plant control system.
--
Tor <bw****@wvtqvm. vw | tr i-za-h a-z>
Leet Jon wrote:
On 2 Nov 2007 at 20:34, Al Balmer wrote:
>>I can understand that for debugging purposes you might want to have
SIGSEGV etc. generate a core file, but in production code the default
should be for these signals to be ignored.
In production code, those signals should never be generated. If they
are, they should crash, so that the user can complain, and someone can
fix it.
Perhaps you are unaware that some C code is run in safety-critical
environments - having a program that dumps core at the drop of a hat
rather than carrying on running could literally be the difference
between life and death. OK, so *maybe* the error condition causing the
SIGSEGV will propagate and bring the program down later, but taking that
chance is a better option than immediately failing.
~Jon~
The error handler which you must provide will bring the controls it is doing
into a state that is normal or safe that won't cause death, ring a klaxon and
turn on a warning light and then crash. It should arrange to make itself not
restartable until it has been pulled from the working environment and placed on
a test bench! Anything else would be criminal.
If that means that the anti-lock brake system light stays on with the check
vehicle light flashing and you are operating on analog backup only then that is
what it means! (To put this into context)
You might obtain a copy of National Bureau of Standards (NBS) Computer Science
and Technology series, Special Publication 500-75, February 1981 "Validation ,
Verification, and Testing of Computer Software" by W. Richards Adrion, Martha A.
Branstad, John C. Cherniavsky. Library of Congress Card Number 80-600199. I'm
sure other publications have followed this, but you will get a sense of what the
responsibility of the programmer is to design a test suite to prove the program
works as expected under all conditions expected and unexpected.
On Fri, 2 Nov 2007 21:16:31 +0100 (CET), Leet Jon <jo*@nospam.com wrote:
>On 2 Nov 2007 at 19:10, Keith Thompson wrote:
>However, letting a program continue running by default after a
catastrophic data-corrupting failure would not be a good idea. If a
program dies immediately after "an invalid access to storage" (which
is all the C standard says about SIGSEGV), then you have a good
chance of diagnosing and correcting the problem before putting the
code into production. If the error is ignored, the program will very
likely continue to corrupt your data in subtle ways; tracking it down
and fixing it is going to be difficult if the error occurs at a
customer site, or even during an important demo.
I believe you are completely wrong on this point. Very often a SIGSEGV
will be caused by (say) a single bad array access - the consequences
will be highly localized, and carrying on with the program will not
cause any significant problems.
So the program may 'think' it has saved the important dataset from a
medical patient's important test, but the data has disappeared because
it was written ... well, nowhere in particular.
Do you *really* want this program to go on?
Leet Jon wrote:
On 2 Nov 2007 at 20:34, Al Balmer wrote:
>>I can understand that for debugging purposes you might want to have
SIGSEGV etc. generate a core file, but in production code the default
should be for these signals to be ignored.
In production code, those signals should never be generated. If they
are, they should crash, so that the user can complain, and someone can
fix it.
Perhaps you are unaware that some C code is run in safety-critical
environments - having a program that dumps core at the drop of a hat
rather than carrying on running could literally be the difference
between life and death.
If a SIGSEGV can be the difference between life and death, then such
code has *no* *right* to ever *cause* a SIGSEGV, regardless of how the
system is going to respond to the SIGSEGV (ignoring it and letting
the program continue, or aborting it).
There are several solutions that could proper here:
(1) Keep the code simple enough that you can use mathematics to
prove it correct. This has been been done successfully with
some designs. It's not easy, but then we're talking about a
life or death situation here.
(2) Exhaustively test the code. Sometimes this is not possible
due to exponential explosion of test cases, but sometimes
it actually is.
(3) Nearly-exhaustively test the code. Maybe testing every possible
program path isn't possible, but very thorough test coverage
(not just of lines of code, but of "interestin g" combination
of inputs) is possible. That might be acceptable if combined
with other quality efforts.
(4) Use a system where, on a *local* basis, *individual* faults can
be determined to be harmless and the program can proceed.
Notice that this is not the same thing as ignoring SIGSEGV
for the entire program and assuming all invalid memory
accesses are OK. Instead, what I'm talking about is a
system where you can say "if THIS block of code goes
outside the bounds of THAT array, then THAT ONE THING
should not be a fatal error, and here is the routine that
will do the error handling and keep the system in a known
good state".
Of course, it's silly to be having a discussion about safety-critical
software in comp.unix.progr ammer. Maybe there's one that I don't know
about, but as far as I know, there isn't a version of Unix that is
meant to be used in an environment like that. In fact, where I've
checked, license agreements often specifically exclude the use of the
software in such an environment. And for good reason: a system that
can get somebody killed needs to use software that's simpler that Unix.
- Logan
Logan Shaw wrote:
<snip>
You might consider dropping c.l.c. from the cross-post and perhaps
replace it with comp.programmin g and set followups to the same.
This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics | |
by: Klaus Neuner |
last post by:
Hello,
consider the following two programs:
# (1)
import sys, signal
def alarm_handler(signum, frame):
raise
|
by: Martin McCormick |
last post by:
A C program contains several signal statements to remove a
lock file if the program gets killed:
/*Set up interrupt handler to catch ctrl-C so that lock file can be removed.*/
signal(SIGINT,crash);
signal(SIGBUS,crash);
signal(SIGSEGV,crash);
This part works. Those signals cause the "crash.c" module to
run and get rid of the lock. Is there a standard way to also print
|
by: LeTubs |
last post by:
Hi
I'm not sure if this is correct ...place to post but here goes
This is what i'm trying to do, I want to write a signal / alarm handler
( I don't know which hence the posting here, as once I know the proper
name /useage then I'll use google to try and find out more
information )....
Thus any tips or pointers would be helpful (and I'm using a UNIX variant as
OS)
|
by: Jackie |
last post by:
Hi everyone,
I'd like to know when and how signals are used (e.g. SIGFPE, SIGABRT,
SIGTERM, SIGSEGV, SIGINT)? Thank you so much.
|
by: None |
last post by:
Hello,
1.
The prototype of function signal in signal.h:
void (*signal(int sig, void (*func)(int)))(int);
is some complex to me. Would you please explain it to me in detail with
the C language syntax itself. Thank you!
| | |
by: Stanley S |
last post by:
Hi,
Are Signal Handling part of ANSI C?
I am not able to find any reference of Sig Handling in Stephen Prata's
"C Primer Plus".
The usage of signals is to trap errors I guess. (It looks similiar to
the concept of try-catch to me.) It seems to relate more to nix OS. Are
signals handling part of Windows too?
|
by: Udai Kiran |
last post by:
Hi all
Iam having trouble with signal handler. Where will the execution
return after invoking a signal handler when that particular signal is
recieved? will return to the point where we register the signal?
The following code is recieveing recursive signals.
2 #include <stdio.h>
3 #include <stdlib.h>
4 #include <unistd.h>
5
|
by: david |
last post by:
I'm developing a program that runs using an asyncore loop. Right now
I can adequately terminate it using Control-C, but as things get
refined I need a better way to stop it. I've developed another
program that executes it as a child process using popen2.Popen4(). I
was attempting to use signals to stop it (using os.kill()) but I keep
running into a problem where sending the signal causes an infinite
loop of printing the message...
|
by: thagor2008 |
last post by:
Is the behaviour of throwing exceptions in a unix signal handler
defined?
eg:
void sighandler(int sig)
{
... do something
throw myobj;
}
|
by: marktang |
last post by:
ONU (Optical Network Unit) is one of the key components for providing high-speed Internet services. Its primary function is to act as an endpoint device located at the user's premises. However, people are often confused as to whether an ONU can Work As a Router. In this blog post, we’ll explore What is ONU, What Is Router, ONU & Router’s main usage, and What is the difference between ONU and Router. Let’s take a closer look !
Part I. Meaning of...
|
by: Oralloy |
last post by:
Hello folks,
I am unable to find appropriate documentation on the type promotion of bit-fields when using the generalised comparison operator "<=>".
The problem is that using the GNU compilers, it seems that the internal comparison operator "<=>" tries to promote arguments from unsigned to signed.
This is as boiled down as I can make it.
Here is my compilation command:
g++-12 -std=c++20 -Wnarrowing bit_field.cpp
Here is the code in...
| | |
by: jinu1996 |
last post by:
In today's digital age, having a compelling online presence is paramount for businesses aiming to thrive in a competitive landscape. At the heart of this digital strategy lies an intricately woven tapestry of website design and digital marketing. It's not merely about having a website; it's about crafting an immersive digital experience that captivates audiences and drives business growth.
The Art of Business Website Design
Your website is...
|
by: agi2029 |
last post by:
Let's talk about the concept of autonomous AI software engineers and no-code agents. These AIs are designed to manage the entire lifecycle of a software development project—planning, coding, testing, and deployment—without human intervention. Imagine an AI that can take a project description, break it down, write the code, debug it, and then launch it, all on its own....
Now, this would greatly impact the work of software developers. The idea...
|
by: isladogs |
last post by:
The next Access Europe User Group meeting will be on Wednesday 1 May 2024 starting at 18:00 UK time (6PM UTC+1) and finishing by 19:30 (7.30PM).
In this session, we are pleased to welcome a new presenter, Adolph Dupré who will be discussing some powerful techniques for using class modules.
He will explain when you may want to use classes instead of User Defined Types (UDT). For example, to manage the data in unbound forms.
Adolph will...
|
by: conductexam |
last post by:
I have .net C# application in which I am extracting data from word file and save it in database particularly. To store word all data as it is I am converting the whole word file firstly in HTML and then checking html paragraph one by one.
At the time of converting from word file to html my equations which are in the word document file was convert into image.
Globals.ThisAddIn.Application.ActiveDocument.Select();...
|
by: TSSRALBI |
last post by:
Hello
I'm a network technician in training and I need your help.
I am currently learning how to create and manage the different types of VPNs and I have a question about LAN-to-LAN VPNs.
The last exercise I practiced was to create a LAN-to-LAN VPN between two Pfsense firewalls, by using IPSEC protocols.
I succeeded, with both firewalls in the same network. But I'm wondering if it's possible to do the same thing, with 2 Pfsense firewalls...
|
by: muto222 |
last post by:
How can i add a mobile payment intergratation into php mysql website.
| | |
by: bsmnconsultancy |
last post by:
In today's digital era, a well-designed website is crucial for businesses looking to succeed. Whether you're a small business owner or a large corporation in Toronto, having a strong online presence can significantly impact your brand's success. BSMN Consultancy, a leader in Website Development in Toronto offers valuable insights into creating effective websites that not only look great but also perform exceptionally well. In this comprehensive...
| |
