Re: MPS: Forwording symbols

["Gerd Möllmann" <gerd.moellmann@gmail.com>]

Gerd Möllmann <gerd.moellmann@gmail.com> writes:

> Helmut Eller <eller.helmut@gmail.com> writes:
>
>> On Mon, Jun 17 2024, Gerd Möllmann wrote:
>>
>>> The whole dumping of these structs looks highly dubious to me,
>>> independent of MPS. They are constants, always have been, AFAICT, even
>>> from what I remember from the 90s.
>>
>> The patch below creates the necessary relocs so that no forwarding
>> structs end up in the dump.
>
> Thanks. pushed.
>
>>
>>> Looking forward to the time when the mirror code is gone :-).
>>
>> I'm not so optimistic.  The first collection is very slow:
>>
>>    time ./emacs -batch -f igc--collect
>>    
>>    real    0m12.555s
>>    user    0m11.708s
>>    sys     0m0.097s
>
> That's pretty slow, indeed. The version of Emacs I'm currently running,
> which is my fork which does not contain your recent changes, and is an
> optimized build with -lmps says
>
> .../emacs/github/igc % /usr/bin/time src/emacs -batch -f igc--collect
>         0.25 real         0.14 user         0.11 sys
>
>> That's not good.  Maybe there is some unfixed problem that is causing
>> this slowness, but it could also be that MPS simply is so slow for this
>> allocation pattern.
>
> I guess it is what you suspect because I run into an assertion when dumping:
>
>   Dumping fingerprint: 79b503a407de48b18f4c304971c234d89bf236c259a1e7cd857559f919943b91
>
>   igc.c:345: Emacs fatal error: assertion failed: h->obj_type == IGC_OBJ_PAD || nbytes >= sizeof (struct igc_fwd)
>   Fatal error 6: Aborted
>
> That's a build starting from git clean -xdf, optimized, -lmps, and no
> native compilation here of course.
>
> I'll try to debug this, but I think I have to read the new code first a
> bit to understand where to start.

Anyway, maybe the following gives you a hint already. The abort happens
with this backtrace while writing the dump

* thread #1, queue = 'com.apple.main-thread', stop reason = breakpoint 5.2
    frame #0: 0x00000001001e3cf8 bootstrap-emacs`emacs_abort at sysdep.c:2391:3
    frame #1: 0x00000001003ec57c bootstrap-emacs`ns_term_shutdown(sig=6) at nsterm.m:5889:5
    frame #2: 0x00000001001a2dbc bootstrap-emacs`shut_down_emacs(sig=6, stuff=(struct Lisp_Symbol *) $2 = 0x0000000100ca5010) at emacs.c:3162:3
    frame #3: 0x00000001001a27a4 bootstrap-emacs`terminate_due_to_signal(sig=6, backtrace_limit=2147483647) at emacs.c:464:11
    frame #4: 0x0000000100399fa4 bootstrap-emacs`igc_assert_fail(file="igc.c", line=345, msg="h->obj_type == IGC_OBJ_PAD || nbytes >= sizeof (struct igc_fwd)") at igc.c:82:3
    frame #5: 0x000000010039cde8 bootstrap-emacs`obj_size(h=0x00000001298085f8) at igc.c:345:3
    frame #6: 0x000000010039cc6c bootstrap-emacs`igc_dump_finish_obj(client=0x0000000129808600, type=IGC_OBJ_DUMPED_BUFFER_TEXT, base="", end="") at igc.c:3721:7
    frame #7: 0x0000000100277fc0 bootstrap-emacs`dump_igc_finish_obj(ctx=0x000000016fdfc3e8) at pdumper.c:910:26
  * frame #8: 0x00000001002840d0 bootstrap-emacs`dump_cold_buffer(ctx=0x000000016fdfc3e8, data=(struct buffer *) $3 = 0x000000010e4d3308) at pdumper.c:3694:3

here:
  char *
  igc_dump_finish_obj (void *client, enum igc_obj_type type,
                       char *base, char *end)
  {
    if (client == NULL)
      return end;

    struct igc_header *out = (struct igc_header *) base;
    if (is_mps (client))
      {
        struct igc_header *h = client_to_base (client);
        if (h->obj_type == IGC_OBJ_VECTOR_WEAK)
          igc_assert (
            (type == IGC_OBJ_VECTOR && h->obj_type == IGC_OBJ_VECTOR_WEAK)
            || h->obj_type == type);
        igc_assert (base + obj_size (h) >= end);

Looks like the client object passed in is bogus

  (lldb) p *h
  (igc_header)  (obj_type = IGC_OBJ_INVALID, hash = 128931976, nwords = 1)
  (lldb)