Re: buffer.c/buffer.h: How to add new buffer-local variables?

[Keith David Bershatsky]

Thank you, Paul, for taking the time to try and reproduce the behavior that I 
am experiencing on my end.

I am assuming that this round of tests is with a current version of the master 
branch (0b8117ed1abfc17bb0bc1690a8997736f1e8f98c) and _after_ applying the 
x.diff patch.  I built the Emacs master branch (current version) without any 
modifications so that the build could complete without errors, and then I 
applied the x.diff patch and built again and then performed the gdb test.  The 
build with the patch will crash on my end when garbage collection occurs; 
however, the ptype test is able to complete and I have attached a gdb printout 
0b8117ed1abfc17bb0bc1690a8997736f1e8f98c.txt.  The current issue is beyond my 
current level of programming abilities to resolve, so other than performing a 
standard M-x diff between your ptype test (relabeled as ptype_by_paul.txt) and 
my own test (0b8117ed1abfc17bb0bc1690a8997736f1e8f98c.txt), I would need 
further guidance regarding how best to be of assistance.

My setup on Windows XP SP-3 didn't recognize a build option of -m32, so I just 
used the same old build options that I have used previously; i.e.,:

CFLAGS='-O0 -g3' ./configure \
--enable-checking='yes,glyphs' \
--enable-check-lisp-object-type \
--without-compress-install \
--without-makeinfo \
--with-gnutls=no \
--with-mailutils \
--without-makeinfo

Keith

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

> Date: [04-07-2019 22:23:07] <7 Apr 2019 22:23:07 -0700>
> From: Paul Eggert <address@hidden>
> To: Keith David Bershatsky <address@hidden>
> Cc: address@hidden, Stefan Monnier <address@hidden>,
> Andreas Schwab <address@hidden>, Alan Mackenzie <address@hidden>,
> Daniel Colascione <address@hidden>
> Subject: Re: buffer.c/buffer.h: How to add new buffer-local variables?
> 
> Keith David Bershatsky wrote:
> > Perhaps there is something that may stand out (to a trained programmer) in 
> > the 01/31/2019 commit ....
> 
> It did change the buffer struct layout, so it's a good candidate for a 
> culprit.
> 
> For what it's worth, I cannot reproduce the problem in a 32-bit build under 
> Fedora 29 x86-64 (GCC 8.3.1). I configured this way:
> 
> ./configure CC=gcc -m32 -march=native --enable-gcc-warnings 
> --without-imagemagick --without-gif --with-modules 
> --enable-checking=yes,glyphs --enable-check-lisp-object-type --with-gnutls=no
> 
> and built Emacs master with the attached patch x.diff.
> 
> My guess is that the problem has something to do with the unportable 
> assumptions we've long made about struct buffer layout. I am attaching 
> ptype.txt, the output of the GDB command "ptype /o current_buffer" that Eli 
> suggested; please compare it to your ptype output.

0b8117ed1abfc17bb0bc1690a8997736f1e8f98c.txt
Description: application/txt

ptype_by_paul.txt
Description: application/txt

x.diff
Description: application/diff