golang/go

runtime: openbsd/arm fails when compiled with GOARM=5

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#54,305 opened on Aug 5, 2022

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NeedsFixarch-armcompiler/runtimehelp wanted

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Description

When the arm architecture is compiled with GOARM=5, the linker rewrites TLS register loads from MRC with a call to runtime.read_tls_fallback - on OpenBSD post 6.9, this fails since runtime.read_tls_fallback is still a direct system call:

https://github.com/golang/go/blob/master/src/runtime/sys_openbsd_arm.s#L90

This code path is generally never hit, since the minimum ARM CPU supported by OpenBSD is v7 and hence GOARM=7 is the default.

We should either:

  1. Revise runtime.read_tls_fallback to use a libc-based system call.

  2. Prevent GOARM < 7 from being used on openbsd/arm and remove the fallback code entirely.

Contributor guide

Research direction
Investigate the read tls fallback function in sys openbsd arm.s and the linker's TLS handling in cmd/link. Choose between adapting the fallback to use libc calls or preventing GOARM<7 and removing the fallback.
Tech stack
go
Domain
compilers
Issue type
Bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
4
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
Half day
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
Git
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
30