Subject: bug#28308: Build failure on FreeBSD/aarch64

From: Gergely Czuczy <[email-masked]>
Date: Mon, 11 Sep 2017 22:33:45 +0200

On 2017. 09. 11. 19:17, Eli Zaretskii wrote:
>> Cc: [email-masked], [email-masked]
>> From: Gergely Czuczy <[email-masked]>
>> Date: Mon, 11 Sep 2017 19:12:12 +0200
>>
>>> That's a call to delete_terminal, which doesn't appear in your
>>> backtrace, and doesn't call xpalloc, either.  So thanks, but I'm still
>>> confused.  Are you sure this is an unoptimized build?  Is it possible
>>> that we are looking at LLDB bug?
>> It's the lldb debug, right. And I'm sure it's an unoptimized build, I've
>> went back and checked the build flags:
>> cc -Demacs  -I. -I. -I../lib -I../lib
>> -I/usr/local/include/libxml2             -MMD -MF deps/.d -MP
>> -Wno-switch -Wno-pointer-sign -Wno-string-plus-int
>> -Wno-unknown-attributes -Wno-initializer-overrides
>> -Wno-tautological-compare
>> -Wno-tautological-constant-out-of-range-compare -O0 -g
>> -fno-strict-aliasing  -Wl,-znocombreloc  (...)
>>
>> If that helps, I can create a qemu VM with this fbsd build, and give you
>> the image.
> Would it be possible for you to install GDB, and then repeat the same
> experiment under GDB?
It was relatively fast, however it appears to be the same:
root@build-pine64:/usr/ports/editors/emacs-devel/work/emacs-f44184f/lisp# 
EMACSLOADPATH= lldb -- '../src/bootstrap-emacs' -batch l-no-site-file 
--no-site-lisp --eval '(setq load-prefer-newer t)' -f batch-byte-compile 
emacs-lisp/macroexp.elk/emacs-f4
(lldb) target create "../src/bootstrap-emacs"
Current executable set to '../src/bootstrap-emacs' (aarch64).
(lldb) settings set -- target.run-args  "-batch" "--no-site-file" 
"--no-site-lisp" "--eval" "(setq load-prefer-newer t)" "-f" 
"batch-byte-compile" "emacs-lisp/macroexp.el"
(lldb) r
Process 98283 launching
Process 98283 launched: '../src/bootstrap-emacs' (aarch64)
Process 98283 stopped
* thread #1, name = 'bootstrap-emacs', stop reason = signal SIGSEGV: 
invalid address (fault address: 0x41b17978)
     frame #0: 0x0000000000228460 
bootstrap-emacs`xnrealloc(pa=0x0000000000000000, nitems=0, 
item_size=1102150015) at alloc.c:939
    936  {
    937    eassert (0 <= nitems && 0 < item_size);
    938    ptrdiff_t nbytes;
-> 939    if (INT_MULTIPLY_WRAPV (nitems, item_size, &nbytes) || 
SIZE_MAX < nbytes)
    940      memory_full (SIZE_MAX);
    941    return xrealloc (pa, nbytes);
    942  }
(lldb) bt
* thread #1, name = 'bootstrap-emacs', stop reason = signal SIGSEGV: 
invalid address (fault address: 0x41b17978)
   * frame #0: 0x0000000000228460 
bootstrap-emacs`xnrealloc(pa=0x0000000000000000, nitems=0, 
item_size=1102150015) at alloc.c:939
     frame #1: 0x0000000000228204 
bootstrap-emacs`xnrealloc(pa=0x000000000019ae38, nitems=42949672960, 
item_size=281474976703896) at alloc.c:939
     frame #2: 0x000000000022e208 
bootstrap-emacs`xpalloc(pa=0x0000000000000000, 
nitems=0x0000000041b1797f, nitems_incr_min=1683000, 
nitems_max=42949672960, item_size=281474976703896) at alloc.c:0
     frame #3: 0x0000000000168214 
bootstrap-emacs`delete_tty(terminal=0x4f67ed32e8e06446) at term.c:4463
     frame #4: 0x0000000000040190 bootstrap-emacs`__start + 376
     frame #5: 0x0000000040390018 ld-elf.so.1`.rtld_start at rtld_start.S:41
(lldb)

It's still in the delete_ttye function, however, 4463 is a call to 
delete_terminal, and not to xpalloc. It's interesting why's that frame 
#2, because lldb also returns the same as we can see in the source:
(lldb) frame select 3
frame #3: 0x0000000000168214 
bootstrap-emacs`delete_tty(terminal=0x4f67ed32e8e06446) at term.c:4463
    4460      before delete_terminal.  */
    4461   reset_sys_modes (tty);
    4462
-> 4463   delete_terminal (terminal);
    4464
    4465   xfree (tty->name);
    4466   xfree (tty->type);

However, disassembly gave something interesting:
** 4463   delete_terminal (terminal);
    4464

     0x16820c <+224>: bl     0xd40b4 ; coordinates_in_window + 5312 at 
window.c:1274
     0x168210 <+228>: bl     0x22e1f8 ; xpalloc + 16084 at alloc.c:992

-> 4465   xfree (tty->name);

->  0x168214 <+232>: bl 0x35b294                  ; 
text_property_stickiness + 628 at textprop.c:1845
     0x168218 <+236>: ldurb  w8, [x29, #-0x2c]
     0x16821c <+240>: tbz    w8, #0x0, 0x16823c ; <+272> at term.c

The pointer is at the xfree call. However, I the disassembly was too 
long, I couldn't get anything useful out of it.
And here's the core file: http://czg.harmless.hu/tmp/bootstrap-emacs.core.gz

You can download and analyze it with lldb, it was in the root of the 
source tree, if that matters. I guess that way you can just open it with 
lldb yourself, and dig into it.