cmd/asm: arm64 assembler generates code that is not execute-only compatible

[4a6f656c]

The Go assembler for arm64 generates code that is not execute-only compatible, since it stores constants in the text section rather than in rodata, which it then reads during execution.

OpenBSD 7.3 has enabled xonly by default on OpenBSD/arm64 - this means that externally linked Go binaries segfault on execution. This can be worked around in the interim by disabling execute-only when the external linker is invoked.

Longer term, the assembler should store constants in rodata and/or load them via instructions, such that the text section can be marked as execute-only.

[dr2chase]

@golang/compiler

[gopherbot]

Change https://go.dev/cl/484555 mentions this issue: cmd/link/internal/ld: disable execute-only for external linking on openbsd/arm64

[randall77]

I know of one place where we read instruction memory, to print instruction bytes after a SIGILL:

https://cs.opensource.google/go/go/+/refs/tags/go1.20.3:src/runtime/signal_unix.go;l=747

Not super critical, but if we're running in execute-only mode it would be good to disable that code.

[erifan]

since it stores constants in the text section rather than in rodata, which it then reads during execution.

Do you mean literal pool ?

[4a6f656c]

since it stores constants in the text section rather than in rodata, which it then reads during execution.

Do you mean literal pool ?

Yes.

[gopherbot]

Change https://go.dev/cl/512538 mentions this issue: cmd/internal/obj/arm64: improve classification of loads and stores

[gopherbot]

Change https://go.dev/cl/512540 mentions this issue: cmd/internal/obj/arm64: improve splitting of 24 bit unsigned scaled immediates