2b462646ed
[This is an unmodified redo of CL 527056.] Standard Ms set g0.stackguard1 to the same value as stackguard0 in mstart0. For consistency, extra Ms should do the same for their g0. Do this in needm -> callbackUpdateSystemStack. Background: getg().stackguard1 is used as the stack guard for the stack growth prolouge in functions marked //go:systemstack [1]. User Gs set stackguard1 to ^uintptr(0) so that the check always fail, calling morestackc, which throws to report a //go:systemstack function call on a user stack. g0 setting stackguard1 is unnecessary for this functionality. 0 would be sufficient, as g0 is always allowed to call //go:systemstack functions. However, since we have the check anyway, setting stackguard1 to the actual stack bound is useful to detect actual stack overflows on g0 (though morestackc doesn't detect this case and would report a misleading message about user stacks). [1] cmd/internal/obj calls //go:systemstack functions AttrCFunc. This is a holdover from when the runtime contained actual C functions. But since CL 2275, it has simply meant "pretend this is a C function, which would thus need to use the system stack". Hence the name morestackc. At this point, this terminology is pretty far removed from reality and should probably be updated to something more intuitive. Change-Id: If315677217354465fbbfbd0d406d79be20db0cc3 Reviewed-on: https://go-review.googlesource.com/c/go/+/527716 Auto-Submit: Michael Pratt <mpratt@google.com> Reviewed-by: Cherry Mui <cherryyz@google.com> LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> |
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