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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at https://mozilla.org/MPL/2.0/. */
#ifndef mozilla_interceptor_Arm64_h
#define mozilla_interceptor_Arm64_h
#include <type_traits>
#include "mozilla/Assertions.h"
#include "mozilla/CheckedInt.h"
#include "mozilla/MathAlgorithms.h"
#include "mozilla/Maybe.h"
#include "mozilla/Result.h"
#include "mozilla/Saturate.h"
#include "mozilla/Types.h"
namespace mozilla {
namespace interceptor {
namespace arm64 {
// clang-format off
enum class IntegerConditionCode : uint8_t {
// From the ARMv8 Architectural Reference Manual, Section C1.2.4
// Description Condition Flags
EQ = 0b0000, // == Z == 1
NE = 0b0001, // != Z == 0
CS = 0b0010, // carry set C == 1
HS = 0b0010, // carry set (alias) C == 1
CC = 0b0011, // carry clear C == 0
LO = 0b0011, // carry clear (alias) C == 0
MI = 0b0100, // < 0 N == 1
PL = 0b0101, // >= 0 N == 0
VS = 0b0110, // overflow V == 1
VC = 0b0111, // no overflow V == 0
HI = 0b1000, // unsigned > C == 1 && Z == 0
LS = 0b1001, // unsigned <= !(C == 1 && Z == 0)
GE = 0b1010, // signed >= N == V
LT = 0b1011, // signed < N != V
GT = 0b1100, // signed > Z == 0 && N == V
LE = 0b1101, // signed <= !(Z == 0 && N == V)
AL = 0b1110, // unconditional <Any>
NV = 0b1111 // unconditional (but AL is the preferred encoding)
};
// clang-format on
struct LoadOrBranch {
enum class Type {
Load,
Branch,
};
// Load constructor
LoadOrBranch(const uintptr_t aAbsAddress, const uint8_t aDestReg)
: mType(Type::Load), mAbsAddress(aAbsAddress), mDestReg(aDestReg) {
MOZ_ASSERT(aDestReg < 32);
}
// Unconditional branch constructor
explicit LoadOrBranch(const uintptr_t aAbsAddress)
: mType(Type::Branch),
mAbsAddress(aAbsAddress),
mCond(IntegerConditionCode::AL) {}
// Conditional branch constructor
LoadOrBranch(const uintptr_t aAbsAddress, const IntegerConditionCode aCond)
: mType(Type::Branch), mAbsAddress(aAbsAddress), mCond(aCond) {}
Type mType;
// The absolute address to be loaded into a register, or branched to
uintptr_t mAbsAddress;
union {
// The destination register for the load
uint8_t mDestReg;
// The condition code for the branch
IntegerConditionCode mCond;
};
};
enum class PCRelCheckError {
InstructionNotPCRel,
NoDecoderAvailable,
};
MFBT_API Result<LoadOrBranch, PCRelCheckError> CheckForPCRel(
const uintptr_t aPC, const uint32_t aInst);
/**
* Casts |aValue| to a |ResultT| via sign extension.
*
* This function should be used when extracting signed immediate values from
* an instruction.
*
* @param aValue The value to be sign extended. This value should already be
* isolated from the remainder of the instruction's bits and
* shifted all the way to the right.
* @param aNumValidBits The number of bits in |aValue| that contain the
* immediate signed value, including the sign bit.
*/
template <typename ResultT>
inline ResultT SignExtend(const uint32_t aValue, const uint8_t aNumValidBits) {
static_assert(std::is_integral_v<ResultT> && std::is_signed_v<ResultT>,
"ResultT must be a signed integral type");
MOZ_ASSERT(aNumValidBits < 32U && aNumValidBits > 1);
using UnsignedResultT = std::decay_t<std::make_unsigned_t<ResultT>>;
const uint8_t kResultWidthBits = sizeof(ResultT) * 8;
// Shift left unsigned
const uint8_t shiftAmt = kResultWidthBits - aNumValidBits;
UnsignedResultT shiftedLeft = static_cast<UnsignedResultT>(aValue)
<< shiftAmt;
// Now shift right signed
auto result = static_cast<ResultT>(shiftedLeft);
result >>= shiftAmt;
return result;
}
inline static uint32_t BuildUnconditionalBranchToRegister(const uint32_t aReg) {
MOZ_ASSERT(aReg < 32);
// BR aReg
return 0xD61F0000 | (aReg << 5);
}
MFBT_API LoadOrBranch BUncondImmDecode(const uintptr_t aPC,
const uint32_t aInst);
/**
* If |aTarget| is more than 128MB away from |aPC|, we need to use a veneer.
*/
inline static bool IsVeneerRequired(const uintptr_t aPC,
const uintptr_t aTarget) {
detail::Saturate<intptr_t> saturated(aTarget);
saturated -= aPC;
uintptr_t absDiff = Abs(saturated.value());
return absDiff >= 0x08000000U;
}
inline static bool IsUnconditionalBranchImm(const uint32_t aInst) {
return (aInst & 0xFC000000U) == 0x14000000U;
}
inline static Maybe<uint32_t> BuildUnconditionalBranchImm(
const uintptr_t aPC, const uintptr_t aTarget) {
detail::Saturate<intptr_t> saturated(aTarget);
saturated -= aPC;
CheckedInt<int32_t> offset(saturated.value());
if (!offset.isValid()) {
return Nothing();
}
// offset should be a multiple of 4
MOZ_ASSERT(offset.value() % 4 == 0);
if (offset.value() % 4) {
return Nothing();
}
offset /= 4;
if (!offset.isValid()) {
return Nothing();
}
uint32_t signbits = static_cast<uint32_t>(offset.value()) & 0xFE000000;
// Ensure that offset is small enough to fit into the 26 bit region.
// We check that the sign bits are either all ones or all zeros.
MOZ_ASSERT(signbits == 0xFE000000 || !signbits);
if (signbits && signbits != 0xFE000000) {
return Nothing();
}
uint32_t masked = static_cast<uint32_t>(offset.value()) & 0x03FFFFFF;
// B imm26
return Some(0x14000000U | masked);
}
/**
* Allocate and construct a veneer that provides an absolute 64-bit branch to
* the hook function.
*/
template <typename TrampPoolT>
inline static uintptr_t MakeVeneer(TrampPoolT& aTrampPool, void* aPrimaryTramp,
const uintptr_t aDestAddress) {
auto maybeVeneer = aTrampPool.GetNextTrampoline();
if (!maybeVeneer) {
return 0;
}
Trampoline<typename TrampPoolT::MMPolicyT> veneer(
std::move(maybeVeneer.ref()));
// Write the same header information that is used for trampolines
veneer.WriteEncodedPointer(nullptr);
veneer.WriteEncodedPointer(aPrimaryTramp);
veneer.StartExecutableCode();
// Register 16 is explicitly intended for veneers in ARM64, so we use that
// register without fear of clobbering anything important.
veneer.WriteLoadLiteral(aDestAddress, 16);
veneer.WriteInstruction(BuildUnconditionalBranchToRegister(16));
return reinterpret_cast<uintptr_t>(veneer.EndExecutableCode());
}
} // namespace arm64
} // namespace interceptor
} // namespace mozilla
#endif // mozilla_interceptor_Arm64_h
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