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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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Go 1.17 adds a new register-based calling convention. While transparent for
most applications, the KVM platform needs special work in a few cases.
First of all, we need the actual address of some assembly functions, rather
than the address of a wrapper. See http://gvisor.dev/pr/5832 for complete
discussion of this.
More relevant to this CL is that ABI0-to-ABIInternal wrappers (i.e., calls from
assembly to Go) access the G via FS_BASE. The KVM quite fast-and-loose about
the Go environment, often calling into (nosplit) Go functions with
uninitialized FS_BASE.
That will no longer work in Go 1.17, so this CL changes the platform to
consistently restore FS_BASE before calling into Go code.
This CL does not affect arm64 code. Go 1.17 does not support the register-based
calling convention for arm64 (it will come in 1.18), but arm64 also does not
use a non-standard register like FS_BASE for TLS, so it may not require any
changes.
PiperOrigin-RevId: 384234305
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Goruntime sets mxcsr once and never changes it.
Reported-by: syzbot+ec55cea6e57ec083b7a6@syzkaller.appspotmail.com
Fixes: #5754
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This allows the package to serve as a general purpose ring0 support package, as
opposed to being bound to specific sentry platforms.
Updates #5039
PiperOrigin-RevId: 355220044
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