Lazy-fpsimd support patch series#1: add Arm64-fpsimd support to arch module

This patch defines the structures and
adds the implementations for fpsimd initialization.

Signed-off-by: Bin Lu <bin.lu@arm.com>

pkg/sentry/arch/arch_aarch64.go

@@ -32,29 +32,35 @@ import (
 const (
 	// SyscallWidth is the width of insturctions.
 	SyscallWidth = 4
+
+	// fpsimdMagic is the magic number which is used in fpsimd_context.
+	fpsimdMagic = 0x46508001
+
+	// fpsimdContextSize is the size of fpsimd_context.
+	fpsimdContextSize = 0x210
 )
 
 // aarch64FPState is aarch64 floating point state.
 type aarch64FPState []byte
 
-// initAarch64FPState (defined in asm files) sets up initial state.
-func initAarch64FPState(data *FloatingPointData) {
-	// TODO(gvisor.dev/issue/1238): floating-point is not supported.
+// initAarch64FPState sets up initial state.
+func initAarch64FPState(data aarch64FPState) {
+	binary.LittleEndian.PutUint32(data, fpsimdMagic)
+	binary.LittleEndian.PutUint32(data[4:], fpsimdContextSize)
 }
 
 func newAarch64FPStateSlice() []byte {
-	return alignedBytes(4096, 32)[:4096]
+	return alignedBytes(4096, 16)[:fpsimdContextSize]
 }
 
 // newAarch64FPState returns an initialized floating point state.
 //
 // The returned state is large enough to store all floating point state
 // supported by host, even if the app won't use much of it due to a restricted
-// FeatureSet. Since they may still be able to see state not advertised by
-// CPUID we must ensure it does not contain any sentry state.
+// FeatureSet.
 func newAarch64FPState() aarch64FPState {
 	f := aarch64FPState(newAarch64FPStateSlice())
-	initAarch64FPState(f.FloatingPointData())
+	initAarch64FPState(f)
 	return f
 }
 
@@ -133,10 +139,10 @@ func (s State) Proto() *rpb.Registers {
 
 // Fork creates and returns an identical copy of the state.
 func (s *State) Fork() State {
-	// TODO(gvisor.dev/issue/1238): floating-point is not supported.
 	return State{
-		Regs:       s.Regs,
-		FeatureSet: s.FeatureSet,
+		Regs:           s.Regs,
+		aarch64FPState: s.aarch64FPState.fork(),
+		FeatureSet:     s.FeatureSet,
 	}
 }
 
@@ -285,8 +291,10 @@ func New(arch Arch, fs *cpuid.FeatureSet) Context {
 	case ARM64:
 		return &context64{
 			State{
-				FeatureSet: fs,
+				aarch64FPState: newAarch64FPState(),
+				FeatureSet:     fs,
 			},
+			[]aarch64FPState(nil),
 		}
 	}
 	panic(fmt.Sprintf("unknown architecture %v", arch))

pkg/sentry/arch/arch_arm64.go

@@ -68,6 +68,7 @@ const (
 // context64 represents an ARM64 context.
 type context64 struct {
 	State
+	sigFPState []aarch64FPState // fpstate to be restored on sigreturn.
 }
 
 // Arch implements Context.Arch.
@@ -75,10 +76,19 @@ func (c *context64) Arch() Arch {
 	return ARM64
 }
 
+func (c *context64) copySigFPState() []aarch64FPState {
+	var sigfps []aarch64FPState
+	for _, s := range c.sigFPState {
+		sigfps = append(sigfps, s.fork())
+	}
+	return sigfps
+}
+
 // Fork returns an exact copy of this context.
 func (c *context64) Fork() Context {
 	return &context64{
-		State: c.State.Fork(),
+		State:      c.State.Fork(),
+		sigFPState: c.copySigFPState(),
 	}
 }
 
@@ -137,8 +147,8 @@ func (c *context64) SetTLS(value uintptr) bool {
 	return false
 }
 
-// SetRSEQInterruptedIP implements Context.SetRSEQInterruptedIP.
-func (c *context64) SetRSEQInterruptedIP(value uintptr) {
+// SetOldRSeqInterruptedIP implements Context.SetOldRSeqInterruptedIP.
+func (c *context64) SetOldRSeqInterruptedIP(value uintptr) {
 	c.Regs.Regs[3] = uint64(value)
 }
 

pkg/sentry/arch/signal_arm64.go

@@ -30,14 +30,27 @@ type SignalContext64 struct {
 	Sp        uint64
 	Pc        uint64
 	Pstate    uint64
-	_pad      [8]byte // __attribute__((__aligned__(16)))
-	Reserved  [4096]uint8
+	_pad      [8]byte       // __attribute__((__aligned__(16)))
+	Fpsimd64  FpsimdContext // size = 528
+	Reserved  [3568]uint8
+}
+
+type aarch64Ctx struct {
+	Magic uint32
+	Size  uint32
+}
+
+type FpsimdContext struct {
+	Head  aarch64Ctx
+	Fpsr  uint32
+	Fpcr  uint32
+	Vregs [64]uint64 // actually [32]uint128
 }
 
 // UContext64 is equivalent to ucontext on arm64(arch/arm64/include/uapi/asm/ucontext.h).
 type UContext64 struct {
 	Flags  uint64
-	Link   *UContext64
+	Link   uint64
 	Stack  SignalStack
 	Sigset linux.SignalSet
 	// glibc uses a 1024-bit sigset_t