runtime/trace: frame pointer unwinding crash on arm64 during async preemption [1.21 backport]

[gopherbot]

@prattmic requested issue #63830 to be considered for backport to the next 1.21 minor release.

@gopherbot Please backport to 1.21. This causes crashes with tracing enabled on arm64. Though the FP code has been broken longer, only in 1.21 did tracing start to depend on the frame pointer.

[gopherbot]

Change https://go.dev/cl/560735 mentions this issue: [release-branch.go1.21] cmd/internal/obj/arm64: fix frame pointer restore in epilogue

[prattmic]

There is technically a workaround here: setting GODEBUG=tracefpunwindoff=1 will disable use of frame pointers with tracing entirely. However, because these crashes are effectively random every single program that enables tracing on arm64 should set this flag to be safe.

Therefore in my opinion we should either backport this fix, or backport a change to set GODEBUG=tracefpunwindoff=1 by default on arm64.

[prattmic]

cc @felixge @nsrip-dd @randall77 @mknyszek

[mknyszek]

The fix was merged in October, so I feel fairly confident that it's safe at this point. It's also pretty small. I'm inclined to approve this.

[gopherbot]

Closed by merging 2fdad8a to release-branch.go1.21.