Re: MPS: unable to build due to assertion violation in igc_dump_check_object_starts

[Gerd Möllmann]

Eli Zaretskii <eliz@gnu.org> writes:

>> From: Gerd Möllmann <gerd.moellmann@gmail.com>
>> Cc: pipcet@protonmail.com,  eller.helmut@gmail.com,  emacs-devel@gnu.org
>> Date: Tue, 23 Jul 2024 20:42:56 +0200
>> 
>> We are inside of the dump_igc_finish_obj. I see nothing immediately
>> suspicious there, hm. 
>> 
>> Can you try to look at that header? It is at offset ctx->igc_base_offset
>> from ctx->buf. Something like
>> 
>>   p header_type ((char *) ctx->buf + ctx->igc_base_offset)
>> 
>> Is it already broken? Depending on where exactly you emacs_abort it
>> either should still be zeroed or contain something valid like type
>> IGC_OBJ_STRING_DATA.
>
> I added emacs_abort here:
>
>   if (ctx->flags.dump_object_contents)
>     {
>       char *base = (char *) ctx->buf + ctx->igc_base_offset;
>       char *end = (char *) ctx->buf + ctx->offset;
>       if (ctx->igc_base_offset == 0x6e6c08)
>       emacs_abort ();  <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
>       eassert (end > base);
>       char *should_end = igc_dump_finish_obj (ctx->igc_obj_dumped, 
> ctx->igc_type, base, end);
>       eassert (should_end >= end);
>       dump_write_zero (ctx, should_end - end);
>       if (ctx->flags.record_object_starts)
>       dump_push (&ctx->igc_object_starts,
>                  list2 (dump_off_to_lisp (ctx->igc_base_offset),
>                         dump_off_to_lisp (ctx->offset)));
>     }
>
> And:
>
>   (gdb) p header_type ((char *) ctx->buf + ctx->igc_base_offset)
>   $10 = IGC_OBJ_STRING_DATA
>
> This is _before_ igc_dump_finish_obj was called.

I can't explain that ATM. The start function

  static void
  dump_igc_start_obj (struct dump_context *ctx, enum igc_obj_type type,
                      const void *in)
  {
    eassert (ctx->igc_type == IGC_OBJ_INVALID);
    eassert (ctx->igc_obj_dumped == NULL);
    eassert (ctx->offset % DUMP_ALIGNMENT == 0);
    ctx->igc_obj_dumped = (void *) in;
    ctx->igc_type = type;
    ctx->igc_base_offset = ctx->offset;
    if (ctx->flags.dump_object_contents &&
        (type == IGC_OBJ_DUMPED_BYTES ||
         type == IGC_OBJ_DUMPED_CODE_SPACE_MASKS))
      {
        /* This saving of obj_offset is Because of an assertion in
           dump_write. */
        dump_off obj_offset = ctx->obj_offset;
        ctx->obj_offset = 0;
        dump_write_zero (ctx, igc_header_size ());
        ctx->obj_offset = obj_offset;
      }
  }

doesn't write the type, unless I'm blind, and the finish function
doesn't either before the emacs_abort. Hm.