Re: Simple exception use-case

[Phil Muldoon <pmuldoon at redhat dot com>]

Daniel Jacobowitz wrote:
> > 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.
> >     
>
> IIRC this is because GDB does not (did not?) use pending breakpoints.
> Try again after starting the program, so libstdc++ is loaded.  If it's
> still broken it's an easy fix.
>   
Ok if I break main, then run, and then finally add the catch throw and 
catch catch, it works. That's another on my list to investigate. But 
while doing this I stumbled onto something interesting. If you look at 
these two test-runs, one from upstream GDB one from a patched Fedora GDB 
you'll see that the Fedora GDB did not loose control of the inferior. 
This test is by no means conclusive, but it intrigues me. For the 
purpose of this use-case and estimation I was going to concentrate 
purely on upstream, but I think I'll take a look at Fedora GDB and 
investigate the patch load. There may be a patch that already fixes 
possible longjmp or other inferior control issues. If so, can look at 
the estimation to convert this patch upstream, tweak it - whatever - 
over writing new support. At the very least I'll investigate why this 
one use-cases diverges on two different GDBs.

** UPSTREAM GDB

~/gdb_obj/gdb/gdb simple
GNU gdb (GDB) 6.8.50.20080728-cvs

(gdb) break main
Breakpoint 1 at 0x400be7: file simple.cxx, line 17.

(gdb) r
Starting program: /home/pmuldoon/exceptions/simple

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

(gdb) catch throw
Catchpoint 2 (throw)

(gdb) c
Continuing.
Catchpoint 2 (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.


** CURRENT FEDORA GDB

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

(gdb) break main
Breakpoint 1 at 0x400be7: file simple.cxx, line 17.

(gdb) r
Starting program: /home/pmuldoon/exceptions/simple
warning: 
"/usr/lib/debug/lib/modules/2.6.25.10-86.fc9.x86_64/vdso/vdso.so.debug": 
The separate debug info file has no debug info

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

(gdb) catch throw
Catchpoint 2 (throw)

(gdb) c
Continuing.

Catchpoint 2 (exception thrown)
__cxa_throw (obj=<value optimized out>, tinfo=<value optimized out>, 
dest=<value optimized out>) at 
../../../../libstdc++-v3/libsupc++/eh_throw.cc:63
63        header->unexpectedHandler = __unexpected_handler;

(gdb) s
58                               void (*dest) (void *))

(gdb) s
71        _Unwind_RaiseException (&header->unwindHeader);

(gdb) s
61        header->exceptionType = tinfo;

(gdb) s
62        header->exceptionDestructor = dest;

(gdb) finish
Run till exit from #0  __cxa_throw (obj=<value optimized out>, 
tinfo=<value optimized out>, dest=<value optimized out>)
   at ../../../../libstdc++-v3/libsupc++/eh_throw.cc:62
0x0000000000400c13 in main () at simple.cxx:17

(gdb) s
19        catch (exception &e)

(gdb) s
__cxa_begin_catch (exc_obj_in=<value optimized out>) at 
../../../../libstdc++-v3/libsupc++/eh_catch.cc:45
45      __cxxabiv1::__cxa_begin_catch (void *exc_obj_in) throw()

(gdb) finish
Run till exit from #0  __cxa_begin_catch (exc_obj_in=<value optimized 
out>) at ../../../../libstdc++-v3/libsupc++/eh_catch.cc:45
0x0000000000400c34 in main () at simple.cxx:19

19        catch (exception &e)
Value returned is $1 = (void *) 0x15fa080

(gdb) s
21            cout << "Exception: " << e.what() << endl;

(gdb) s
simple::what (this=0x15fa080) at simple.cxx:10
10          return "simple exception occurred";

(gdb) s

11        }

(gdb) c
Continuing.
Exception: simple exception occurred

Program exited normally.