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authorJamie Liu <jamieliu@google.com>2021-10-08 18:00:36 -0700
committergVisor bot <gvisor-bot@google.com>2021-10-08 18:03:23 -0700
commit3f1642e4bc86c6e7febc6b2dd2b83ad48c5ee201 (patch)
treed7b6428e36cda75eb7a8702d22923cc13c22f0cc /website
parent34e68b6b4ff04de5c7b5e2dc46e5bd44c6845e63 (diff)
Remove ring0 floating point save/load functions on amd64.
ring0.Save/LoadFloatingPoint() are only usable if the caller can ensure that Go will not clobber floating point registers before/after calling them respectively. Due to regabig in Go 1.17, this is no longer the case; regabig (among other things) maintains a zeroed XMM15 during ABIInternal execution, including by zeroing it after ABI0-to-ABIInternal transitions. In ring0.sysenter/exception, this happens in ring0.kernelSyscall/kernelException.abi0 respectively; in ring0.CPU.SwitchToUser, this happens after returning from ring0.sysret/iret.abi0. Delete these functions and do floating point save/load in assembly. While arm64 doesn't appear to be immediately affected (so this CL permits us to resume usage of Go 1.17), its use of Save/LoadFloatingPoint() still seems to be incorrect for the same fundamental reason (Go code can't sanely assume what registers the Go compiler will or won't use) and should be fixed eventually. PiperOrigin-RevId: 401895658
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