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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/. */
#include "Arm64.h"
#include "mozilla/ResultVariant.h"
namespace mozilla {
namespace interceptor {
namespace arm64 {
struct PCRelativeLoadTest {
// Bitmask to be ANDed with the instruction to isolate the bits that this
// instance is interested in
uint32_t mTestMask;
// The desired bits that we want to see after masking
uint32_t mMatchBits;
// If we match, mDecodeFn provide the code to decode the instruction.
LoadOrBranch (*mDecodeFn)(const uintptr_t aPC, const uint32_t aInst);
};
static LoadOrBranch ADRPDecode(const uintptr_t aPC, const uint32_t aInst) {
// Keep in mind that on Windows aarch64, uint32_t is little-endian
const uint32_t kMaskDataProcImmPcRelativeImmLo = 0x60000000;
const uint32_t kMaskDataProcImmPcRelativeImmHi = 0x00FFFFE0;
uintptr_t base = aPC;
intptr_t offset = SignExtend<intptr_t>(
((aInst & kMaskDataProcImmPcRelativeImmHi) >> 3) |
((aInst & kMaskDataProcImmPcRelativeImmLo) >> 29),
21);
base &= ~0xFFFULL;
offset <<= 12;
uint8_t reg = aInst & 0x1F;
return LoadOrBranch(base + offset, reg);
}
MFBT_API LoadOrBranch BUncondImmDecode(const uintptr_t aPC,
const uint32_t aInst) {
int32_t offset = SignExtend<int32_t>(aInst & 0x03FFFFFFU, 26);
return LoadOrBranch(aPC + offset);
}
// Order is important here; more specific encoding tests must be placed before
// less specific encoding tests.
static const PCRelativeLoadTest gPCRelTests[] = {
{0x9FC00000, 0x10000000, nullptr}, // ADR
{0x9FC00000, 0x90000000, &ADRPDecode}, // ADRP
{0xFF000000, 0x58000000, nullptr}, // LDR (literal) 64-bit GPR
{0x3B000000, 0x18000000, nullptr}, // LDR (literal) (remaining forms)
{0x7C000000, 0x14000000, nullptr}, // B (unconditional immediate)
{0xFE000000, 0x54000000, nullptr}, // B.Cond
{0x7E000000, 0x34000000, nullptr}, // Compare and branch (imm)
{0x7E000000, 0x36000000, nullptr}, // Test and branch (imm)
{0xFE000000, 0xD6000000, nullptr} // Unconditional branch (reg)
};
/**
* In this function we interate through each entry in |gPCRelTests|, AND
* |aInst| with |test.mTestMask| to isolate the bits that we're interested in,
* then compare that result against |test.mMatchBits|. If we have a match,
* then that particular entry is applicable to |aInst|. If |test.mDecodeFn| is
* present, then we call it to decode the instruction. If it is not present,
* then we assume that this particular instruction is unsupported.
*/
MFBT_API Result<LoadOrBranch, PCRelCheckError> CheckForPCRel(
const uintptr_t aPC, const uint32_t aInst) {
for (auto&& test : gPCRelTests) {
if ((aInst & test.mTestMask) == test.mMatchBits) {
if (!test.mDecodeFn) {
return Err(PCRelCheckError::NoDecoderAvailable);
}
return test.mDecodeFn(aPC, aInst);
}
}
return Err(PCRelCheckError::InstructionNotPCRel);
}
} // namespace arm64
} // namespace interceptor
} // namespace mozilla
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