🔒 Locked

Exceptions

Started by walkingcarcass May 11, 2003 at 11:30 AM 22 replies 1.1k views

Original Post

May 11, 2003 at 11:30 AM

In an exception handler, how can I get the address of the instruction which raised an exception? I''m not afraid of using assembly here. ******** A Problem Worthy of Attack Proves It''s Worth by Fighting Back

dalleboy

May 11, 2003 at 12:24 PM

What kind of exception are you talking about? C++ exceptions, Win32 Structured Exceptions or something else?

Update GameDev.net system time campaign - success at last

dede

May 11, 2003 at 1:36 PM

You can''t really, but you can number each exception. (assuming you are rolling your own), and then tell that way. Its not end-user friendly, but it can be useful.

walkingcarcass

Author

walkingcarcass

May 11, 2003 at 2:24 PM

The exception handler must have some mechanism to return to the code if the exception has been accomodated. I recall something about a chain of data structures and the FS register...?

********

A Problem Worthy of Attack
Proves It''s Worth by Fighting Back

risingdragon3

May 11, 2003 at 2:27 PM

There is no such thing, in C++. Handling does NOT go back to the point of exception after the exception handler is finished.

I dunno about Win32 Structured Exceptions though.

Thunder_Hawk

May 11, 2003 at 2:35 PM

You shouldn't really have a problem with this if you are saving exceptions for fatal sorts of problems (like running out of memory). If you're looking for the line number for debugging purposes, you can pull it off with a little simple macro work

[edited by - Thunder_Hawk on May 11, 2003 3:37:32 PM]

walkingcarcass

Author

walkingcarcass

May 11, 2003 at 2:47 PM

If execution doesn''t resume after an exception, how can the program possibly continue running?

********

A Problem Worthy of Attack
Proves It''s Worth by Fighting Back

antareus

May 11, 2003 at 2:52 PM

quote:
Original post by walkingcarcass
If execution doesn''t resume after an exception, how can the program possibly continue running?

When an exception is thrown, the stack unwinds and the exception handlers are run on the exception until it either:
1. unwinds through main, at which point you get an "unhandled exception" dialog box and the program forcibly terminates.
2. reaches a handler that does not rethrow the exception. Execution continues after this handler as usual.

walkingcarcass

Author

walkingcarcass

May 11, 2003 at 3:05 PM

You mean the code immediately after in memory, like the exception doesn''t have a ret? WOAH! Red flag! I can imagine abandoning a function halfway through causing some really nasty problems, corruptions, leaks etc

what *exactly* (in micro-detail) is the sequence of events when an exception is thrown?

********

A Problem Worthy of Attack
Proves It''s Worth by Fighting Back

Jan Wassenberg

105

Jan Wassenberg

May 11, 2003 at 3:16 PM

fs points to the thread (info | environment) block; its first field is a pointer to the head of the exception handler chain.
fs -> tib
tib[0] -> head
head[0] -> new handler
head[1] -> old handler(s)
This handler receives an EXCEPTION_RECORD*, which tells you the address of the instruction that bombed.
Return value specifies continue, next handler, or default.

We need to differentiate between SEH and C++ exceptions. As soon as your code causes a processor exception to be raised, the Windows handler gets control. It examines the handler list, and calls them sequentially (unless one decides to continue execution, in which case the instruction is restarted).

Austrian Coder

May 11, 2003 at 3:23 PM

Removed!

[edited by - Austrian Coder on May 11, 2003 4:43:10 PM]

antareus

May 11, 2003 at 3:50 PM

quote:
Original post by walkingcarcass
I can imagine abandoning a function halfway through causing some really nasty problems, corruptions, leaks etc

Destructors are run as the stack unwinds. Use resource acquisition is initialization idiom for resources whenever possible, and std::auto_ptr for those you use operator new on.

walkingcarcass

Author

walkingcarcass

May 11, 2003 at 4:07 PM

forget deconstructors, auto pointers etc, if my exception handler can "fix" the problem (eg divide by zero sets FPU stack top to very a big number) then how can execution continue from the bad instruction? Is there a danger of screwing up some kind of exeption handler stack?

********

A Problem Worthy of Attack
Proves It''s Worth by Fighting Back

bjmumblingmiles

May 11, 2003 at 6:40 PM

You''re trying to redirect the divide by zero error? Thats only for integers anyway, and you cant catch that kind of exception like that...but floats do not have the same problem because there isnt a float 0. You can usually only catch non-syntactical errors, like something just didnt work, not memory read errors etc.

Brian J

Qw3r7yU10p!

May 12, 2003 at 2:28 AM

Herb Sutter wrote the books ''Exceptional C++'' and ''More Exceptional C++'' based on his online column ''Guru of the Week''. They are articles that pose a question and then a few days, weeks or months later (after much discussion on comp.lang.c++.moderated) he will post a comprehensive answer. They look at all the tough areas of C++, language features and design issues etc. If you do a text search on that page for ''exception'' you''ll find about 10 or 12 articles that deal with exception issues. Here are just a few that might get you going.

quote:
Code Complexity - Part I
Difficulty: 9 / 10

This problem presents an interesting challenge: How many execution paths can there be in a simple three-line function? The answer will almost certainly surprise you.

quote:

Try and Catch Me
Difficulty: 3 / 10

Is exception safety all about writing try and catch in the right places? If not, then what? And what kinds of things should you consider when developing an exception safety policy for your software?

quote:

Constructor Failures
Difficulty: 7 / 10

What exactly happens when a constructor emits an exception? What if the exception comes from an attempt to construct a subobject or member object? This issue of GotW analyzes one aspect of C++ in detail, shows why it should work the way that it does, and demonstrates the implications for constructor exception specifications.

walkingcarcass

Author

walkingcarcass

May 12, 2003 at 6:04 AM

This is not a C++ speific question. When something goes wrong and the processor detects an exception, it goes through the OS defined process of calling exception handlers until a suitable one is found, right?

Once execution enters an exception handler, what information is a vailable and how does the program continue.

********

A Problem Worthy of Attack
Proves It''s Worth by Fighting Back

Kylotan

Mod

3,487

Kylotan

May 12, 2003 at 8:28 AM

quote:
Original post by walkingcarcass
This is not a C++ specific question.

walkingcarcass

Author

walkingcarcass

May 12, 2003 at 11:39 AM

Are exceptions themselves C++ specific? No! Is it my fault you assumed it was a C++ question? No! Was there any hint in the question that I meant C++? No!

I don''t want to sart flaming here, but it''s a bit precious to accuse me of wasting time.

The original question is simple, direct, and unambiguous.

********

A Problem Worthy of Attack
Proves It''s Worth by Fighting Back

Arild Fines

138

Arild Fines

May 12, 2003 at 12:43 PM

Unlike more sophisticated languages, C++ doesn''t allow you to retrieve a stack trace from the exception object.

...and that is why I believe linux must be destroyed.

Kylotan

Mod

3,487

Kylotan

May 14, 2003 at 6:05 AM

quote:
Original post by walkingcarcass
Are exceptions themselves C++ specific? No! Is it my fault you assumed it was a C++ question? No! Was there any hint in the question that I meant C++? No!

How are exceptions used by most people on these boards? As programming language features. What programming language is used the most here? C++. So that is a very reasonable assumption for people to make given that the scope for potential answers is massive without you providing more information. Yet, you ignored the guy who tried to help refine your question right at the start. And have you not still refused to even specify what processor you want to do this on? If you want answers, ask a decent question in the first place, and try helping those who try to help you.

quote:
The original question is simple, direct, and unambiguous.

Topic Locked

This topic has been locked by a moderator. New replies are not allowed.