Re: GDB AIX build broken

[Pedro Alves <palves at redhat dot com>]

On 10/25/2016 01:51 AM, David Edelsohn wrote:
> On Mon, Oct 24, 2016 at 8:31 PM, Pedro Alves <palves@redhat.com> wrote:
>> On 10/25/2016 01:13 AM, David Edelsohn wrote:
>>> On Mon, Oct 24, 2016 at 7:00 PM, Pedro Alves <palves@redhat.com> wrote:
>>>
>>>> That's a hint, but it can't be the fix.  common-defs.h must be the
>>>> first file included.  I suspect that gnulib's inttypes.h
>>>> replacement logic is broken on AIX.
>>>
>>> The gnulib import definitely is the commit that caused the breakage.
> 
> gnulib weaves between its header files and the system header files in
> dangerous ways.  It incorrectly assumes that it's version of a header
> file always will be seen before a system header file.  But a system
> header file may include another system header file directly.

Sure, and if so, gnulib will be patched to handle it somehow.

> 
> 
> AIX inttypes.h protects the printf format macros with
> 
> #if !defined(__cplusplus) || defined(__STDC_FORMAT_MACROS)

There you go.  See my other email.  This means AIX's
headers haven't been updated for C++11 yet.  C++11 overruled
C99's decision to require the __STDC_FORMAT_MACROS input macro,
and the C11 followed suit.

> 
> gnulib inttypes.h helpfully provides
> 
>    /* Some pre-C++11 <stdint.h> implementations need this.  */
> #  if defined __cplusplus && ! defined __STDC_FORMAT_MACROS
> #   define __STDC_FORMAT_MACROS 1
> #  endif
> 
> #  include_next <inttypes.h>
> # endif
> #endif

Right, that old way of defining __STDC_FORMAT_MACROS isn't complete.
That's why I wrote the fix at:
https://lists.gnu.org/archive/html/bug-gnulib/2015-11/msg00010.html
That now defines __STDC_FORMAT_MACROS in config.h instead.  Now the
problem is that gnulib's configure runs with a C compiler,
not a C++ compiler, so my fix doesn't really make a difference.   I had
written that assuming we'd change to configure/build gnulib
with a C++ compiler, back then.

So the fix is to do what I had suggested here
<https://sourceware.org/ml/gdb-patches/2016-10/msg00522.html>:

~~~~~~
                                              If this causes a problem
    somewhere, we can re-define the macros higher up in the file, before
    system headers are included.
~~~~~~

> Should __STDC_FORMAT_MACROS be defined in gdb/common/common-defs.h and
> gdb/defs.h (if btrace.c also is changed)?

Exactly, almost.  Only common/common-defs.h should be changed.
defs.h includes common/common-defs.h first thing,
before system headers.  ("common" refers to the file being
shared between gdb and gdbserver.)

Thanks,
Pedro Alves