From: "Gerd Möllmann" <gerd.moellmann@gmail.com>
To: Helmut Eller <eller.helmut@gmail.com>
Cc: emacs-devel@gnu.org
Subject: Re: MPS symbols
Date: Fri, 28 Jun 2024 09:42:25 +0200 [thread overview]
Message-ID: <m2msn5cy3i.fsf@pro2.fritz.box> (raw)
In-Reply-To: <87r0chwnzx.fsf@gmail.com> (Helmut Eller's message of "Fri, 28 Jun 2024 09:00:18 +0200")
Helmut Eller <eller.helmut@gmail.com> writes:
> I have trouble to understand how symbols work with MPS.
>
> A Lisp_Object that references a symbol has tag Lisp_Symbol (0) and the
> other bits are an offset (in bytes) from lispsym.
>
> How can MPS recognize ambiguous references to symbols?
I hope I got that right (I think I have). Let me cite the scanner
function for simpliciry:
scan_ambig (mps_ss_t ss, void *start, void *end, void *closure)
{
MPS_SCAN_BEGIN (ss)
{
for (mps_word_t *p = start; p < (mps_word_t *) end; ++p)
{
mps_word_t word = *p;
mps_word_t tag = word & IGC_TAG_MASK;
/* If the references in the object being scanned are
ambiguous then MPS_FIX2() does not update the
reference (because it can't know if it's a
genuine reference). The MPS handles an ambiguous
reference by pinning the block pointed to so that
it cannot move. */
mps_addr_t ref = (mps_addr_t) word;
mps_res_t res = MPS_FIX12 (ss, &ref);
if (res != MPS_RES_OK)
return res;
Ambiguous referencess can be either pointers or Lisp_Objects. The above
lines handle the pointer case, and below is the Lisp_Object case, that
is when it looks kuje a Lisp_Object.
switch (tag)
{
case Lisp_Int0:
case Lisp_Int1:
case Lisp_Type_Unused0:
break;
case Lisp_Symbol:
{
ptrdiff_t off = word ^ tag;
ref = (mps_addr_t) ((char *) lispsym + off);
res = MPS_FIX12 (ss, &ref);
if (res != MPS_RES_OK)
return res;
}
break;
And anove is the symbol case. I.e. the word looks like Lisp_Object of a
symbol, we do the offset thing and rely on MPS_FIX12 to to the right ting.
default:
ref = (mps_addr_t) (word ^ tag);
res = MPS_FIX12 (ss, &ref);
if (res != MPS_RES_OK)
return res;
break;
And the above is basically fhe same as for symbols, only that we don't have
to do the offset dance.
}
}
}
MPS_SCAN_END (ss);
return MPS_RES_OK;
}
next prev parent reply other threads:[~2024-06-28 7:42 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-06-28 7:00 MPS symbols Helmut Eller
2024-06-28 7:42 ` Gerd Möllmann [this message]
2024-06-28 7:53 ` Helmut Eller
2024-06-28 8:37 ` Gerd Möllmann
2024-06-28 8:46 ` Gerd Möllmann
2024-06-28 9:19 ` Gerd Möllmann
2024-06-28 11:54 ` Helmut Eller
2024-06-28 12:13 ` Gerd Möllmann
2024-06-28 12:36 ` Gerd Möllmann
2024-06-28 11:16 ` Eli Zaretskii
2024-06-28 11:50 ` Gerd Möllmann
2024-06-28 13:47 ` Helmut Eller
2024-06-28 14:13 ` Gerd Möllmann
2024-06-28 14:46 ` Gerd Möllmann
2024-06-28 15:41 ` Helmut Eller
2024-06-28 16:06 ` Eli Zaretskii
2024-06-28 16:19 ` Helmut Eller
2024-06-28 17:40 ` Eli Zaretskii
2024-06-28 16:20 ` Gerd Möllmann
2024-06-28 17:59 ` Eli Zaretskii
2024-06-29 3:56 ` Gerd Möllmann
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