From:	"Kalum Somaratna aka Grendel" <kalum AT newmail DOT net>
To:	djgpp AT delorie DOT com
Date:	Sun, 21 Nov 1999 06:02:46 +0600
MIME-Version:	1.0
Subject:	Re: Issues with 'gxx -O -fomit-frame-pointer' and exceptions?
In-reply-to:	<e$yOxAAUCtN4EAR0@lwithers.demon.co.uk>
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On 20 Nov 99, at 16:47, Laurence Withers wrote:

> 
> I have come across something I don't understand when compiling code.
> Whilst writing a small utility, I found that if you catch a C++
> exception in main() and then return, the program will crash if you have
> compiled it with the options '-O -fomit-frame-pointer' (that's -O, -O2
> or -O3).
> 
> 'gcc -v':
> 
>   Reading specs from c:/bin/djgpp/lib/specs
>   gcc version 2.95 19990728 (release)
> 
> - sample program -------------------------------------------------------
> #include <iostream>
> 
> class Exception { };
> 
> int main()
> {
>     try {
>         char c = 0;
>         cout << "Throw exception [yY]? ";
>         cin.get(c);
>         if(c == 'y' || c == 'Y') {
>             cout << "Throwing..." << endl;
>             throw Exception();
>         }
>         cout << "No exception..." << endl;
>     }
>     catch(...) {
>         cout << "Exception caught..." << endl;
>         return -1;
>     }
>     cout << "No error." << endl;
>     return 0;
> }
> - end ------------------------------------------------------------------
> 
> Try compiling with 'gcc -O -fomit-frame-pointer -g -o test.exe test.cpp'
> and then running. If you enter y or Y, the exception will be caught but
> the program will crash. Any other key, and there is no crash.
> 
> Now compile without -fomit-frame-pointer, and there is no crash. Compile
> without -O, and there is no crash.
> 

This is to say that I also compiled and ran your program using 
GCC2.95.2 (the latest) and your problem still is in it.

I compiled your program using "gcc -O3 -fomit-frame-pointer t.cpp -
o t.exe -lstdcx -g"

And it also crashed giving the output below.

Throw exception [yY]? y
Throwing...
Exception caught...
Exiting due to signal SIGSEGV
General Protection Fault at eip=00001704
eax=ffffffff ebx=000a7cdc ecx=00000010 edx=00027884 
esi=00000054 edi=0002797c
ebp=000a7970 esp=000a794c program=D:\D\T.EXE
cs: sel=00a7  base=822ae000  limit=000bffff
ds: sel=00af  base=822ae000  limit=000bffff
es: sel=00af  base=822ae000  limit=000bffff
fs: sel=0087  base=0001ac50  limit=0000ffff
gs: sel=00bf  base=00000000  limit=0010ffff
ss: sel=00af  base=822ae000  limit=000bffff
App stack: [000a797c..0002797c]  Exceptn stack: 
[00027858..00025918]

Call frame traceback EIPs:
  0x00001704   _main+336, line 19 of t.cpp



Line 19 of your source happens to be the "return -1;" statement.

I am not quite familiar with c++ syntatics but I happened to have a 
copy of Borland C 4.5 and with it your program compiled OK and 
threw the exception without crashing. So it may be a compiler bug?

Kalum.

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