bug#39577: 27.0.60; Assertion failed during compilation

[Henrik Grimler <hgrimler@kth.se>]

Hi Eli,

On Thu, Feb 13, 2020 at 04:57:26PM +0200, Eli Zaretskii wrote:
> > Date: Wed, 12 Feb 2020 08:39:58 +0100
> > From: Henrik Grimler <henrik@grimler.se>
> > 
> > ../configure --enable-checking=yes,glyphs \
> > --enable-check-lisp-object-type \
> > --without-makeinfo \
> > --without-selinux \
> > --prefix /data/data/com.termux/files/usr/local \
> > CFLAGS="-O0 -g3 -gdwarf-4"
> > ```
> > 
> > but building the emacs-27 branch (commit 06c302d) this fails with:
> > 
> > ```
> > [...]
> > Loading /data/data/com.termux/files/home/projects/emacs/lisp/emacs-lisp/syntax.el (source)...
> > Loading /data/data/com.termux/files/home/projects/emacs/lisp/font-lock.el (source)...
> > Loading /data/data/com.termux/files/home/projects/emacs/lisp/jit-lock.el (source)...
> > 
> > ../../src/fns.c:2856: Emacs fatal error: assertion failed: !FIXNUM_OVERFLOW_P (lisp_h_make_fixnum_n)
> 
> This would mean that the values returned by getloadavg on that system
> are preposterously large.  Can you run the offending command under a
> debugger, put a breakpoint on line 2856 of fns.c, and see what values
> you get in the load_ave[] array?
 
It seems to be preposterously small:

```
Breakpoint 2, Fload_average (use_floats=XIL(0)) at ../../src/fns.c:2856
2856                              ? make_fixnum (100.0 * load_ave[loads])
(gdb) print load_ave
$1 = {2.8900000000000001, 2.8752811112650786e-312, 2.7799999999999998}
```

This android version does not have getloadavg (so I guess
lib/getloadavg.c is used instead?)
 
> > If I remove --enable-checking=yes,glyphs it builds (I am sending this
> > bug report from that build) but gets segmentation faults every now and
> > then. Easiest way to trigger it is to scroll up and down in some file,
> > but it still happens randomly, maybe after 200 lines, maybe after 10
> > 000.
> 
> Can you show a backtrace from the segfault?

After loading gdbinit from emacs src, starting emacs and scrolling up
and down a file a couple of times it crashes with:

```
Program received signal SIGSEGV, Segmentation fault.
0xb6995228 in sigsetjmp () from /system/lib/libc.so
```

A backtrace then unfortunately only shows:

```
#0  0xb6995228 in sigsetjmp () from /system/lib/libc.so
#1  0x62e31f80 in ?? ()
Backtrace stopped: previous frame identical to this frame (corrupt stack?)

Program received signal SIGSEGV, Segmentation fault.
backtrace_top () at ../../src/eval.c:176
176     {
The program being debugged was signaled while in a function called from GDB.
GDB remains in the frame where the signal was received.
To change this behavior use "set unwindonsignal on".
Evaluation of the expression containing the function
(backtrace_top) will be abandoned.
When the function is done executing, GDB will silently stop.
```

I am fairly in-experienced with gdb, so please let me know if there is
anything else I can try.

It also seems that the segfault does not happen if running inside
tmux.