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

1 files changed, 3 insertions, 0 deletions

diff --git a/pkg/ring0/offsets_amd64.go b/pkg/ring0/offsets_amd64.go
index 75f6218b3..38fe27c35 100644
--- a/pkg/ring0/offsets_amd64.go
+++ b/pkg/ring0/offsets_amd64.go
@@ -35,6 +35,9 @@ func Emit(w io.Writer) {
 	fmt.Fprintf(w, "#define CPU_ERROR_CODE       0x%02x\n", reflect.ValueOf(&c.errorCode).Pointer()-reflect.ValueOf(c).Pointer())
 	fmt.Fprintf(w, "#define CPU_ERROR_TYPE       0x%02x\n", reflect.ValueOf(&c.errorType).Pointer()-reflect.ValueOf(c).Pointer())
 	fmt.Fprintf(w, "#define CPU_ENTRY            0x%02x\n", reflect.ValueOf(&c.kernelEntry).Pointer()-reflect.ValueOf(c).Pointer())
+	fmt.Fprintf(w, "#define CPU_HAS_XSAVE        0x%02x\n", reflect.ValueOf(&c.hasXSAVE).Pointer()-reflect.ValueOf(c).Pointer())
+	fmt.Fprintf(w, "#define CPU_HAS_XSAVEOPT     0x%02x\n", reflect.ValueOf(&c.hasXSAVEOPT).Pointer()-reflect.ValueOf(c).Pointer())
+	fmt.Fprintf(w, "#define CPU_FPU_STATE        0x%02x\n", reflect.ValueOf(&c.floatingPointState).Pointer()-reflect.ValueOf(c).Pointer())
 
 	e := &kernelEntry{}
 	fmt.Fprintf(w, "\n// CPU entry offsets.\n")