On 02/13/2013 03:33 PM, Glenn Morris wrote:

> since it apparently worked in Emacs 24.2, then in emacs-24
> branch at this stage we should just do the minimum to get
> it back to that working state, and save improvements for trunk.

We can certainly give that a try.  Looking at unexaix.c, the
changes made between 24.2 and 24.2.93 are small.  The first
change to unexaix.c, in emacs-24 bzr 108226
<http://bzr.savannah.gnu.org/lh/emacs/emacs-24/revision/108226>,
fixed a bug privately reported to me by Gilles on
2012-05-09; he already tested this so it shouldn't be the
problem.  The remaining changes are small: it shouldn't hurt
to undo them but the real problem surely lies elsewhere.

I see two main suspects.  First, we got rid of DATA_START
and DATA_SEG_BITS on AIX.  Second, USE_LSB_TAG changed from
0 to 1 on AIX.

And now that I look at the code again, I see a serious bug
in Emacs 24.2.93's src/lisp.h when DATA_SEG_BITS is nonzero:
it mis-defines XPNTR as if DATA_SEG_BITS were zero.  This is a
regression and should be fixed in emacs-24 regardless of the
AIX fixes, I expect.

So: Gilles, can you please try the following?

First, aply the attached patch to a fresh copy of emacs-24.2.93.

Then, run these shell commands:

   ./configure CPPFLAGS='-DDATA_START=0x20000000 -DDATA_SEG_BITS=0x20000000 -DUSE_LSB_TAG=0'
   make

If this works, I'll have some followup questions and
proposed changes; the point of the above is to try to test
reverting to 24.2's approach as quickly and painlessly as
possible, without reverting all the other changes we've
made.