Simple exception use-case

[Phil Muldoon <pmuldoon at redhat dot com>]

I want to start building these cases to guide the requirements for 
better C++ exception handling in GDB. I'll start with existing 
technology, and a novice C++ programmer. Example program:

cat simple.cxx

#include <iostream>
#include <exception>

using namespace std;

class simple : public exception
{
 virtual const char* what() const throw()
 {
   return "simple exception occurred";
 }
} simple;

int main () {
 try 
   {
     throw simple;
   }
 catch (exception &e) 
   {
     cout << "Exception: " << e.what() << endl;
   }
 return 0;
}

In this scenario, I just want to catch the: "simple" exception type 
being thrown. There are differences between Fedora's GDB (my chosen 
distribution), and upstream GDB. For now, assume I am using upstream, 
and a "recent" build (mine was built from today's CVS).

Generic exception catching mentions:

help catch

<snip useful info>

Raised exceptions may be caught:
   catch throw - all exceptions, when thrown
   catch throw <exceptname>  - a particular exception, when thrown
   catch catch - all exceptions, when caught
   catch catch <exceptname>  - a particular exception, when caught

So a programmer can catch all exceptions, or named exceptions. There is 
also C++ specific information:

C++ exceptions may be caught:
   catch throw - all exceptions, when thrown
   catch catch - all exceptions, when caught

So for this simple use-case, I'll just stick with catch throw and catch 
catch.

Build my simple C++ application:

g++ -g simple.cxx -o simple

and load it into GDB and tell GDB to catch C++ exceptions:

~/gdb_obj/gdb/gdb simple
GNU gdb (GDB) 6.8.50.20080728-cvs
(gdb) catch throw
Catchpoint 1 (throw)

Run the program:

(gdb) run
Starting program: /home/pmuldoon/exceptions/simple
Catchpoint 1 (exception thrown), 0x000000333d0c3d70 in __cxa_throw () 
from /usr/lib64/libstdc++.so.6

Well it caught something, but what?

(gdb) list
8      virtual const char* what() const throw()
9      {
10        return "simple exception occurred";
11      }
12    } simple;
13   
14    int main () {
15      try 
16        {
17          throw simple;


Well I think it is "throw simple", that is the last line shown. But it 
would be neat if the catch would print the actual throw line, like a 
simple breakpoint. Shown below:

(gdb) break main
Breakpoint 1 at 0x400be7: file simple.cxx, line 17.
(gdb) run
Starting program: /home/pmuldoon/exceptions/simple

Breakpoint 1, main () at simple.cxx:17
17          throw simple;

Anyway, there seems to be no debuginfo associated with the libstdc++ 
blobs. I'll just step  until I return to my program and through the 
catch statement. Then I can look at the exception object in detail:

Catchpoint 1 (exception thrown), 0x000000333d0c3d70 in __cxa_throw () 
from /usr/lib64/libstdc++.so.6
(gdb) s
Single stepping until exit from function __cxa_throw,
which has no line number information.
Exception: simple exception occurred

Program exited normally.

Well maybe not.  I'm not sure why I lost control of the inferior. I'll 
investigate the debuginfo. This is Fedora specific but similar would 
apply for any distribution:

rpm -q gcc-debuginfo
gcc-debuginfo-4.3.0-8.x86_64

I know debuginfo is stored in /usr/lib/debug

find -type f -name "libstdc*"
./usr/lib64/libstdc++.so.6.0.10.debug

rpm -qf `pwd`/usr/lib64/libstdc++.so.6.0.10.debug
gcc-debuginfo-4.3.0-8.x86_64

So I do have debuginfo. I'm puzzled. Ok lets try the GDB 
tailored/packaged to the distribution:

gdb simple
GNU gdb Fedora (6.8-11.fc9)

(gdb) catch catch
Function "__cxa_begin_catch" not defined.
(gdb) catch throw
Function "__cxa_throw" not defined.

No luck there. So I have a simple use case to solve. Comments?

Regards

Phil