3beaf26e4f
Currently, newstack and gogo have write barriers for maintaining the context register saved in g.sched.ctxt. This is troublesome, because newstack can be called from go:nowritebarrierrec places that can't allow write barriers. It happens to be benign because g.sched.ctxt will always be nil on entry to newstack *and* it so happens the incoming ctxt will also always be nil in these contexts (I think/hope), but this is playing with fire. It's also desirable to mark newstack go:nowritebarrierrec to prevent any other, non-benign write barriers from creeping in, but we can't do that right now because of this one write barrier. Fix all of this by observing that g.sched.ctxt is really just a saved live pointer register. Hence, we can shade it when we scan g's stack and otherwise move it back and forth between the actual context register and g.sched.ctxt without write barriers. This means we can save it in morestack along with all of the other g.sched, eliminate the save from newstack along with its troublesome write barrier, and eliminate the shenanigans in gogo to invoke the write barrier when restoring it. Once we've done all of this, we can mark newstack go:nowritebarrierrec. Fixes #22385. For #22460. Change-Id: I43c24958e3f6785b53c1350e1e83c2844e0d1522 Reviewed-on: https://go-review.googlesource.com/72553 Run-TryBot: Austin Clements <austin@google.com> TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: Rick Hudson <rlh@golang.org> Reviewed-by: Cherry Zhang <cherryyz@google.com> |
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