1 files changed, 89 insertions, 0 deletions
diff --git a/toolkit/xre/dllservices/mozglue/interceptor/Arm64.cpp b/toolkit/xre/dllservices/mozglue/interceptor/Arm64.cpp
new file mode 100644
index 0000000000..81d8e6d09b
--- /dev/null
+++ b/toolkit/xre/dllservices/mozglue/interceptor/Arm64.cpp
@@ -0,0 +1,89 @@
+/* -*- 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