enable pkg/sentry/arch to support arm64 basically

Signed-off-by: Bin Lu <bin.lu@arm.com>
Change-Id: I9cce23db4e5caec82ce42b4970fdb7f7e8c08f1d
COPYBARA_INTEGRATE_REVIEW=https://github.com/google/gvisor/pull/773 from lubinszARM:pr_arch_basic 3fe2fd8e6286766bbe489ef971dce204f924feba
PiperOrigin-RevId: 289795569

1 files changed, 126 insertions, 0 deletions

diff --git a/pkg/sentry/arch/signal_arm64.go b/pkg/sentry/arch/signal_arm64.go
new file mode 100644
index 000000000..7d0e98935
--- /dev/null
+++ b/pkg/sentry/arch/signal_arm64.go
@@ -0,0 +1,126 @@
+// Copyright 2020 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package arch
+
+import (
+	"encoding/binary"
+	"syscall"
+
+	"gvisor.dev/gvisor/pkg/abi/linux"
+	"gvisor.dev/gvisor/pkg/sentry/usermem"
+)
+
+// SignalContext64 is equivalent to struct sigcontext, the type passed as the
+// second argument to signal handlers set by signal(2).
+type SignalContext64 struct {
+	FaultAddr uint64
+	Regs      [31]uint64
+	Sp        uint64
+	Pc        uint64
+	Pstate    uint64
+	_pad      [8]byte // __attribute__((__aligned__(16)))
+	Reserved  [4096]uint8
+}
+
+// UContext64 is equivalent to ucontext on arm64(arch/arm64/include/uapi/asm/ucontext.h).
+type UContext64 struct {
+	Flags  uint64
+	Link   *UContext64
+	Stack  SignalStack
+	Sigset linux.SignalSet
+	// glibc uses a 1024-bit sigset_t
+	_pad [(1024 - 64) / 8]byte
+	// sigcontext must be aligned to 16-byte
+	_pad2 [8]byte
+	// last for future expansion
+	MContext SignalContext64
+}
+
+// NewSignalAct implements Context.NewSignalAct.
+func (c *context64) NewSignalAct() NativeSignalAct {
+	return &SignalAct{}
+}
+
+// NewSignalStack implements Context.NewSignalStack.
+func (c *context64) NewSignalStack() NativeSignalStack {
+	return &SignalStack{}
+}
+
+// SignalSetup implements Context.SignalSetup.
+func (c *context64) SignalSetup(st *Stack, act *SignalAct, info *SignalInfo, alt *SignalStack, sigset linux.SignalSet) error {
+	sp := st.Bottom
+
+	if !(alt.IsEnabled() && sp == alt.Top()) {
+		sp -= 128
+	}
+
+	// Construct the UContext64 now since we need its size.
+	uc := &UContext64{
+		Flags: 0,
+		Stack: *alt,
+		MContext: SignalContext64{
+			Regs:   c.Regs.Regs,
+			Sp:     c.Regs.Sp,
+			Pc:     c.Regs.Pc,
+			Pstate: c.Regs.Pstate,
+		},
+		Sigset: sigset,
+	}
+
+	ucSize := binary.Size(uc)
+	if ucSize < 0 {
+		panic("can't get size of UContext64")
+	}
+	// st.Arch.Width() is for the restorer address. sizeof(siginfo) == 128.
+	frameSize := int(st.Arch.Width()) + ucSize + 128
+	frameBottom := (sp-usermem.Addr(frameSize)) & ^usermem.Addr(15) - 8
+	sp = frameBottom + usermem.Addr(frameSize)
+	st.Bottom = sp
+
+	// Prior to proceeding, figure out if the frame will exhaust the range
+	// for the signal stack. This is not allowed, and should immediately
+	// force signal delivery (reverting to the default handler).
+	if act.IsOnStack() && alt.IsEnabled() && !alt.Contains(frameBottom) {
+		return syscall.EFAULT
+	}
+
+	// Adjust the code.
+	info.FixSignalCodeForUser()
+
+	// Set up the stack frame.
+	infoAddr, err := st.Push(info)
+	if err != nil {
+		return err
+	}
+	ucAddr, err := st.Push(uc)
+	if err != nil {
+		return err
+	}
+
+	// Set up registers.
+	c.Regs.Sp = uint64(st.Bottom)
+	c.Regs.Pc = act.Handler
+	c.Regs.Regs[0] = uint64(info.Signo)
+	c.Regs.Regs[1] = uint64(infoAddr)
+	c.Regs.Regs[2] = uint64(ucAddr)
+
+	return nil
+}
+
+// SignalRestore implements Context.SignalRestore.
+// Only used on intel.
+func (c *context64) SignalRestore(st *Stack, rt bool) (linux.SignalSet, SignalStack, error) {
+	return 0, SignalStack{}, nil
+}