RISC-V: "Illegal instruction" crash when vector instructions detected by V8

Version

v26.5.0 (but any v26 and above is affected)

Platform

Linux firefly 6.18.3 #2 SMP PREEMPT_DYNAMIC Wed May 13 16:58:11 CST 2026 riscv64 GNU/Linux

Subsystem

V8

What steps will reproduce the bug?

run npm or any node-gyp on a SpacemiT-K3 board. Also fails in the build-addons step with make run-ci as that executes node-gyp. Other boards such as the SpacemiT-K1 do not show the crash (Both should have vector instructions available)

How often does it reproduce? Is there a required condition?

100% of the time

What is the expected behavior? Why is that the expected behavior?

There should be no crash when running npm

What do you see instead?

Illegal Instruction

Additional information

Based on the fact that https://github.com/sxa/node/commit/1ecdd388f13391c55cffd9aea580770e1d26a952 fixes it seems likely that this was introduced as part of the vector instructions introduced in https://github.com/v8/v8/commit/de361fd2544a89c0c94fd820f987378edbb98fce - I haven't yet tracked it down to any specific operation in that function. At the moment I've also only determined that it fixes the initial crash and hopefully that doesn' uncover more issues.

FYI @luhenry @luyahan @nodejs/platform-riscv64

Split out from https://github.com/nodejs/build/issues/4099#issuecomment-4935757486

Reproduce with npm or node-gyp on a SpacemiT-K3 under riscv64 Linux, and compare against a K1; also check the build-addons path run by make run-ci. Read the V8 vector-instruction change de361fd2544a89c0c94fd820f987378edbb98fce alongside the reported workaround 1ecdd388f13391c55cffd9aea580770e1d26a952. Done means these commands no longer raise Illegal Instruction on K3 without regressing the K1.