How do I force my code to universally seg fault?

Question

I was wondering what the best way would be to reliably segmentation fault a piece of C code?

I'm fully aware that this is bad behavior, and should never be used in a piece of software, but I wanted to know how I could consistantly force it to happen.

EDIT: The answer I got was not what I originally was looking for, but is valuable in understanding why this question doesn't have a reliable answer.

Reliably with respect to your particular platform, or in a platform independent manner? — Mad Physicist, Jul 16 '17 at 03:44
`kill(getpid(), SIGSEGV);` - technical this isn't caused by a segfault, and are POSIX facilities, but it might be a useful way to examine whatever it is you're trying to observe. — Brett Hale, Jul 16 '17 at 04:34
I cannot see why this is getting downvoted. Sure, it's an odd request, but that should not matter. — klutt, Jul 16 '17 at 04:38
@klutt Without narrowing down the platform it's far too broad. — Retired Ninja, Jul 16 '17 at 05:37
@RetiredNinja I disagree. Wanting a reliable and portable way to get a certain effect is not a very broad question. Unfortunately, there's no solution, but it's still a good question. — klutt, Jul 16 '17 at 05:49
@klutt Good question or not, if it's too broad to be answered it's off topic here. — Retired Ninja, Jul 16 '17 at 07:03
@RetiredNinja Again, I disagree completely. It is a very specific question, and the answer is short. There is no such statement that is guaranteed to result in a segfault on all platforms. — klutt, Jul 16 '17 at 07:41
@klutt You're right. No is a good, short, perhaps unsatisfying to the asker, answer, but it is totally accurate. :) — Retired Ninja, Jul 16 '17 at 17:08

effbiae · Accepted Answer · 2017-07-16T05:55:06.480

It's hard to define a method to segmentation fault a program on undefined platforms. A segmentation fault is a loose term that is not defined for all platforms (eg. simple small computers).

Considering only the operating systems that support processes, processes can receive notification that a segmentation fault occurred.

Further, limiting operating systems to 'unix like' OSes, a reliable method for a process to receive a SIGSEGV signal is kill(getpid(),SIGSEGV)

As is the case in most cross platform problems, each platform may (an usually does) have a different definition of seg-faulting.

But to be practical, and answer the EDIT2, current mac, lin and win OSes will segfault on

*(int*)0 = 0;

Further, it's not bad behaviour to cause a segfault. Some implementations of assert() cause a SIGSEGV signal which might produce a core file. Very useful when you need to autopsy.

What's worse than causing a segfault is hiding it:

try
{
     anyfunc();
}
catch (...) 
{
     printf("?\n");
}

which hides the origin of an error and all you've got to go on is:

.

*What is a segmentation fault* https://stackoverflow.com/questions/2346806/what-is-a-segmentation-fault — effbiae, Jul 16 '17 at 05:38

hedgar2017 · Answer 2 · 2017-07-16T03:51:56.490

1

Just try to read or write to an illegal memory location. For example:

memset(NULL, 1, 1);

Here you are writing a one to address 0, definitely illegal.

edited Jul 16 '17 at 03:51

answered Jul 16 '17 at 03:44

hedgar2017

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Not really a zero-sized array, but an invalid memory location. – Matteo Italia Jul 16 '17 at 03:48
Yeah, you're right, I'm too sleepy xD – hedgar2017 Jul 16 '17 at 03:52
@RetiredNinja well there is no way to force a segfault on every platform. Obviously any answer to this is going to only work in some subset of circumstances – M.M Jul 16 '17 at 03:57
@M.M why can you not force a seg fault on every platform? – Erich Jul 16 '17 at 04:03
There are exotic platforms with unusual memory manager's behavior. But I assumed the author uses Windows or one of popular Linux distros. – hedgar2017 Jul 16 '17 at 04:05
1

@Erich some platforms don't have memory segmentation – M.M Jul 16 '17 at 04:30

score 1 · Answer 3 · answered Jul 16 '17 at 04:06

C language itself doesn't specify anything about segmentation fault. It says the behavior is undefined if you try to access an invalid memory. Segmentation fault or SIGSEGV is a common signal from some underlying platforms to denote invalid memory access. But obviously the underlying platform can decide how it want to behave on such error.

Having saying that, if you are strict about C and "Preferrably regardless of platform" manner then there is no way to force this which will work on every platform on the world.

How do I force my code to universally seg fault?

3 Answers3