Re: Issue with Latest GDB on AIX with GCC-6.12

[Nitish Kumar Mishra <mishra dot nitish dot 88 at gmail dot com>]

Hi All,
>> Yes, but I thought that there was a later comment that GCC 4.8 also
showed problems.
GCC-4.8.5 is working correctly, I have pasted the OP in earlier mail.

>>We know the exception should be caught in frame #12.  But somehow,
the run time unwinder doesn't realize this, and calls std::terminate,
meaning it can't find a matching catch for the thrown exception.
This suggests that the unwinder can't unwind some frame from the
set of frames #0 to frame #12.  The suggestion was to _add_ try/catch
blocks in some frames between #0 - #12, and do some printing in the
added catch blocks.  For example, wrap frame #6, i.e., the
kill_command function, by renaming it to kill_command_org
and add:

I tried adding try/catch block earlier in throw_it and
throw_exception_cxx functions
but got no significant results.
I had tried adding try catch block in these functions:
kill_command
command_handler
command_line_handler
execute_command
throw_it
throw_exception_cxx,
but no progress. Output is exactly same as we got earlier (Other than
extra frames for new
try catch functions). None of the print statements in catch blocks for
above functions worked.


Thanks and Regards,
Nitish


On Tue, Feb 7, 2017 at 7:45 PM, David Edelsohn <dje.gcc@gmail.com> wrote:
> On Tue, Feb 7, 2017 at 8:56 AM, Pedro Alves <palves@redhat.com> wrote:
>> On 02/07/2017 01:44 PM, David Edelsohn wrote:
>>> On Tue, Feb 7, 2017 at 5:30 AM, Pedro Alves <palves@redhat.com> wrote:
>>>
>>>> Speaking of compilers, we know that building gdb with gcc 4.8.5
>>>> doesn't run into this.  Do we know that changed?  Did, for example,
>>>> AIX switch from sjlj to dwarf-based exceptions between gcc 4.8.5
>>>> and 6.1?  Might also be useful to try to build gdb with current
>>>> gcc trunk / gcc 7.
>>>
>>> I cannot tell if some have reported that GCC 4.8.5 works correctly or not.
>>
>> The OP said it works fine on GCC 4.8.5 here:
>>
>>  https://sourceware.org/ml/gdb/2017-01/msg00044.html
>
> Yes, but I thought that there was a later comment that GCC 4.8 also
> showed problems.
>
> There was a change in the encoding of data for AIX, but not a change
> to the basic EH frames or handlers.  AIX did not change EH mechanisms
> and never used SJLJ -- at least not for a very long time.
>
> One test is to use shared libraries to link GDB.
>
> Another possible contribution is the AIX address space.  There have
> been reports in the past of EH frames not sorted correctly and libgcc
> EH not finding exception handlers because it terminated the search
> early.
>
> Thanks, David