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

[Pedro Alves <palves at redhat dot com>]

On 01/25/2017 01:52 PM, Pedro Alves wrote:
> On 01/25/2017 11:12 AM, Pedro Alves wrote:
>> On 01/25/2017 10:54 AM, Nitish Kumar Mishra wrote:
>>> Hi,
>>>
>>> The latest community gdb is not working with gcc 6.12, however, it
>>> works expectedly fine with GCC-4.8.5 on AIX platform.
>>
>> What is gcc 6.12 ?
>>
>>> #12 0x000000010007d994 in _ZL23gdb_rl_callback_handlerPc
>>> (rl=0x1100e92b0 "") at event-top.c:213
>>
>> I only saw C++ frames up to here, and the exception should
>> be caught here.  I don't immediately see why that wouldn't
>> be working, though maybe it's the "noexcept"?  If you remove
>> that, does it fix it?  Maybe we need a level of indirection
>> here too, like in gdb_rl_callback_read_char_wrapper_noexcept
>> / gdb_rl_callback_read_char_wrapper.
> 
> I could reproduce this on gcc119 on the compile farm (AIX 7.2),
> which has GCC 6.1.  I tried the workaround suggested above, but
> that didn't work.
> 
> TBC, it's perfectly valid for a noexpect function to
> try/catch inside as long as no exception escapes out, but,
> compiler bugs are not unheard-of.
> 
> I also tried replacing the TRY/CATCH macros with try/catch(...)
> thinking that it could be something with broken type info,
> and the runtime somehow not figuring out that that catch
> should really catch the exception.  Same thing, doesn't work
> for me.
> 
> So I'm out of ideas.  It looks like a toolchain/runtime bug
> to me.

Sounds like a manifestation of:

 Bug 60939 - AIX: exceptions not caught when calling function via pointer 
 https://gcc.gnu.org/bugzilla/show_bug.cgi?id=60939

since ui->input_handler is a function pointer here:

static void
gdb_rl_callback_handler (char *rl) noexcept
{
  struct gdb_exception gdb_rl_expt = exception_none;
  struct ui *ui = current_ui;

  TRY
    {
      ui->input_handler (rl);
    }
  CATCH (ex, RETURN_MASK_ALL)
    {
      gdb_rl_expt = ex;
    }
  END_CATCH

> 
> TBC, I'm not going to be looking at this further.  It's
> very uncomfortable for me to use that machine --- I get a
> bit too high latency, and emacs doesn't work.  I even tried
> to survive with vi, but then DEL/BS didn't work for me.  :-P

Thanks,
Pedro Alves