Re: Exception handling information in the macintosh

[Jack Howarth <howarth at bromo dot med dot uc dot edu>]

On Thu, Feb 04, 2010 at 08:12:10PM +0100, jacob navia wrote:
> Hi
>
> I have developed a JIT for linux 64 bits. It generates exception  
> handling information
> according to DWARF under linux and it works with gcc 4.2.1.
>
> I have recompiled the same code under the Macintosh and something has  
> changed,
> apparently, because now any throw that passes through my code crashes.
>
> Are there any differences bertween the exception info format between the
> macintosh and linux?
>
> The stack@the moment of the throw looks like this:
>
>    CPP code compiled with gcc  4.2.1 calls
>    JIT code generated on the fly by my JIT compiler that calls
>    CPP code compiled with gcc 4.2.1 that throws. The catch
>    is in the CPP code
>   The throw must go through the JIT code, so it needs the DWARF frame  
> descriptions
> that I generate. Apparently there is a difference.
>
> Thanks in advance for any information.
>
> jacob
>
>

Jacob,
    Are you compiling on darwin10 and using the Apple or FSF
gcc compilers? If you are using Apple's, this question should
be on the darwin-devel mailing list instead. I would mention
though that darwin10 is problematic in that the libgcc and its
unwinder calls are now subsumed into libSystem. This means that
regardless of how you try to link in libgcc, the new code in
libSystem will always be used. For darwin10, Apple decided to
default their linker over to compact unwind which causes problems
with some of the java testcases on gcc 4.4.x. This is fixed for
FSF gcc 4.5 by forcing the compiler to always link with the
-no_compact_unwind option. Another complexity is that Apple
decided to silently abort some of the libgcc calls (now in
libSystem) that require access to FDEs like _Unwind_FindEnclosingFunction().
The reasoning was that the default behavior (compact unwind info) doesn't
use FDEs.
   This is fixed for gcc 4.5 by http://gcc.gnu.org/ml/gcc-patches/2009-12/msg00998.html.
If you are using any other unwinder call that is now silently
aborting, let me know as it may be another that we need to re-export
under a different name from libgcc_ext. Alternatively, you may
be able to work around this issue by using -mmacosx-version-min=10.5
under darwin10.
       Jack