assembly implementation for arm64

[RaduBerinde]

What would it take to have an assembly implementation for arm64? It looks like avo does not support it (at least not yet): mmcloughlin/avo#189

[klauspost]

@RaduBerinde I think starting with a block decompressor would be the most feasible. I definitely wouldn't wait for avo.

I don't really have much personal arm assembly experience - the s2 arm64 asm was mostly just tweaking from the Snappy original.

It could actually be fun to see how far we could get with AI converting the AMD64 asm. Though I lack any arm64 to test/debug.

[RaduBerinde]

Thanks! I might take a stab at it when I have some time for a side project.

[klauspost]

FWIW Grok spat out this after thinking for 5 minutes: https://gist.github.com/klauspost/0450b709d4082ebfa3f2140e31cc85c9

No idea if it anything near useful.

[RaduBerinde]

Probably a decent starting point but it needs a lot of fixing up (I fixed the register names Xi->Ri, extra dot in branch instructions, and there are still a lot of unrecognized instructions and such).

[klauspost]

Yeah. (You probably figured) I just fed it the x64 asm, asking it to convert it to plan 9 arm64 assembly.

Since you are actively looking at it, once you get something compiling, here are some debugging hints.

Using the FuzzDecode is a good start. go test -run=none -fuzz=FuzzDecode will compare asm against the Go reference.

If there is a mismatch, it will dump the data in an errs folder.

You can then use mz d --block-debug broken-file.mzb, and it will print the matches as they are decoded, with the source/detination offset, so you can locate the "instruction" that is wrong, by comparing the input and output.

[klauspost]

You can of course shoot any question you may have to me here.

[klauspost]

#29 arm64 decoder.