On 2/16/25 06:58, Richard Henderson wrote:
the label member is merely a pointer to the instruction text to
be updated with the relative address of the constant, the primary
data is the constant data pool at the end of translation blocks.
this relates more closely to .data sections in offline codegen
if we were to imagine a translation block has .text and .data.
No, it doesn't. It relates most closely to data emitted within .text,
accessed via pc-relative instructions with limited offsets.
This isn't a thing you'd have ever seen on x86 or x86_64, but it is
quite common for arm32 (12-bit offsets), sh4 (8-bit offsets), m68k (16-
bit offsets) and such. Because the offsets are so small, they could
even be placed *within* functions not just between them.
I mentioned before I like the idea and have thought about architectures
with constant streams and constant branch units.
say for arguments sake we considered it 'TCData' with embedded label and
reloc (the purpose is the constant after after all, just it is not a
TCGTemp, it's an explicitly reified constant in the codegen emitters).
wondering if we could add a "disposition" field to control placement.
TCG_DISP_TEXT_TB, TCG_DISP_DATA, etc. this way you could ask the code
generator to do something more conventional while still supporting the
short relative constant islands. "disposition" might be better than
section as a name. also a DATA section could be mmap R without X perms
to lessen the risk of injecting code as constants.
disposition; "the way in which something is placed or arranged,
especially in relation to other things."
TCGConstant is another alternative I would consider as okay. distinct
from TCGTemp of type TEMP_CONST which is heavier weight. it makes one
wonder about reification of large implicit constants as opposed to the
explicitly emitted ones we are talking about here.
TCGConstant might be better.
i'm looking at a TCG source-compatible code generator as an option so I
may experiment locally. it is a private interface at the moment anyhow.
that just seemed inconsistent as most structure definitions are in the
header. but I understand it is a private interface.
the patch was code comprehension. i'm studying TCG interfaces and code
at the moment. i'd like to stay source compatible as much as possible.
Michael.
