On 12/20/23 10:41, Palmer Dabbelt wrote:
On Wed, 20 Dec 2023 10:25:00 PST (-0800), jeffreya...@gmail.com wrote:
On 12/20/23 11:21, Palmer Dabbelt wrote:
Yea, the implementation relies largely on just pushing stuff into the
constant pool, so we're largely independent ABI stuff with the likely
exception being relocations.
Ya, but I think we'd only need the relocations if we were going to try
relaxing stuff. We'd kicked around some ideas there: we could
de-duplicate constant pools or inline smaller constants. That's all way
to complex to try and get into this upcoming binutils release, though
(doubly so with this LEB128 ABI break we're still trying to deal with).
Agreed. And note that de-duplication is mostly implemented without need
for the target to do anything. I was kindof amazed to see some of the
places it kicked in on other ports I've worked with.
I think all we'd need from GCC is some way to get the "this load is a
constant pool address that can be messed with" relocation in there,
the linker would do all the heavy lifting. That's probably just a new
assembler pseudo, so pretty much nothing on the compiler side of things.
In theory (and I did not test this), it should be possible to use
large
code model codegen in a smaller mode and it should interoperate. I
seriously pondered doing that as an additional test, then figured I
had
other higher priority items on my list.
IMO we should test that. At least the common case of a medlow libc
linked into medany programs should be easy.
+Patrick: let's add some configs to the CI for this?
I was pondering a one-off by turning on the large code model by default,
then doing a bootstrap & regression test in QEMU. But integrated into
CI is even better.
OK, let's just add it to CI -- it'd be essentially the same testing,
just it'll stick around.
ACK :)
Patrick
Jeff
