1 files changed, 314 insertions, 0 deletions
diff --git a/js/src/wasm/WasmGC.cpp b/js/src/wasm/WasmGC.cpp
new file mode 100644
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+++ b/js/src/wasm/WasmGC.cpp
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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:
+ *
+ * Copyright 2019 Mozilla Foundation
+ *
+ * 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.
+ */
+
+#include "wasm/WasmGC.h"
+#include "wasm/WasmInstance.h"
+#include "jit/MacroAssembler-inl.h"
+
+using mozilla::DebugOnly;
+
+using namespace js;
+using namespace js::jit;
+using namespace js::wasm;
+
+wasm::StackMap* wasm::ConvertStackMapBoolVectorToStackMap(
+    const StackMapBoolVector& vec, bool hasRefs) {
+  wasm::StackMap* stackMap = wasm::StackMap::create(vec.length());
+  if (!stackMap) {
+    return nullptr;
+  }
+
+  bool hasRefsObserved = false;
+  size_t i = 0;
+  for (bool b : vec) {
+    if (b) {
+      stackMap->setBit(i);
+      hasRefsObserved = true;
+    }
+    i++;
+  }
+  MOZ_RELEASE_ASSERT(hasRefs == hasRefsObserved);
+
+  return stackMap;
+}
+
+// Generate a stackmap for a function's stack-overflow-at-entry trap, with
+// the structure:
+//
+//    <reg dump area>
+//    |       ++ <space reserved before trap, if any>
+//    |               ++ <space for Frame>
+//    |                       ++ <inbound arg area>
+//    |                                           |
+//    Lowest Addr                                 Highest Addr
+//
+// The caller owns the resulting stackmap.  This assumes a grow-down stack.
+//
+// For non-debug builds, if the stackmap would contain no pointers, no
+// stackmap is created, and nullptr is returned.  For a debug build, a
+// stackmap is always created and returned.
+//
+// The "space reserved before trap" is the space reserved by
+// MacroAssembler::wasmReserveStackChecked, in the case where the frame is
+// "small", as determined by that function.
+bool wasm::CreateStackMapForFunctionEntryTrap(
+    const wasm::ArgTypeVector& argTypes, const RegisterOffsets& trapExitLayout,
+    size_t trapExitLayoutWords, size_t nBytesReservedBeforeTrap,
+    size_t nInboundStackArgBytes, wasm::StackMap** result) {
+  // Ensure this is defined on all return paths.
+  *result = nullptr;
+
+  // The size of the wasm::Frame itself.
+  const size_t nFrameBytes = sizeof(wasm::Frame);
+
+  // The size of the register dump (trap) area.
+  const size_t trapExitLayoutBytes = trapExitLayoutWords * sizeof(void*);
+
+  // This is the total number of bytes covered by the map.
+  const DebugOnly<size_t> nTotalBytes = trapExitLayoutBytes +
+                                        nBytesReservedBeforeTrap + nFrameBytes +
+                                        nInboundStackArgBytes;
+
+  // Create the stackmap initially in this vector.  Since most frames will
+  // contain 128 or fewer words, heap allocation is avoided in the majority of
+  // cases.  vec[0] is for the lowest address in the map, vec[N-1] is for the
+  // highest address in the map.
+  StackMapBoolVector vec;
+
+  // Keep track of whether we've actually seen any refs.
+  bool hasRefs = false;
+
+  // REG DUMP AREA
+  wasm::ExitStubMapVector trapExitExtras;
+  if (!GenerateStackmapEntriesForTrapExit(
+          argTypes, trapExitLayout, trapExitLayoutWords, &trapExitExtras)) {
+    return false;
+  }
+  MOZ_ASSERT(trapExitExtras.length() == trapExitLayoutWords);
+
+  if (!vec.appendN(false, trapExitLayoutWords)) {
+    return false;
+  }
+  for (size_t i = 0; i < trapExitLayoutWords; i++) {
+    vec[i] = trapExitExtras[i];
+    hasRefs |= vec[i];
+  }
+
+  // SPACE RESERVED BEFORE TRAP
+  MOZ_ASSERT(nBytesReservedBeforeTrap % sizeof(void*) == 0);
+  if (!vec.appendN(false, nBytesReservedBeforeTrap / sizeof(void*))) {
+    return false;
+  }
+
+  // SPACE FOR FRAME
+  if (!vec.appendN(false, nFrameBytes / sizeof(void*))) {
+    return false;
+  }
+
+  // INBOUND ARG AREA
+  MOZ_ASSERT(nInboundStackArgBytes % sizeof(void*) == 0);
+  const size_t numStackArgWords = nInboundStackArgBytes / sizeof(void*);
+
+  const size_t wordsSoFar = vec.length();
+  if (!vec.appendN(false, numStackArgWords)) {
+    return false;
+  }
+
+  for (WasmABIArgIter i(argTypes); !i.done(); i++) {
+    ABIArg argLoc = *i;
+    if (argLoc.kind() == ABIArg::Stack &&
+        argTypes[i.index()] == MIRType::RefOrNull) {
+      uint32_t offset = argLoc.offsetFromArgBase();
+      MOZ_ASSERT(offset < nInboundStackArgBytes);
+      MOZ_ASSERT(offset % sizeof(void*) == 0);
+      vec[wordsSoFar + offset / sizeof(void*)] = true;
+      hasRefs = true;
+    }
+  }
+
+#ifndef DEBUG
+  // We saw no references, and this is a non-debug build, so don't bother
+  // building the stackmap.
+  if (!hasRefs) {
+    return true;
+  }
+#endif
+
+  // Convert vec into a wasm::StackMap.
+  MOZ_ASSERT(vec.length() * sizeof(void*) == nTotalBytes);
+  wasm::StackMap* stackMap = ConvertStackMapBoolVectorToStackMap(vec, hasRefs);
+  if (!stackMap) {
+    return false;
+  }
+  stackMap->setExitStubWords(trapExitLayoutWords);
+
+  stackMap->setFrameOffsetFromTop(nFrameBytes / sizeof(void*) +
+                                  numStackArgWords);
+#ifdef DEBUG
+  for (uint32_t i = 0; i < nFrameBytes / sizeof(void*); i++) {
+    MOZ_ASSERT(stackMap->getBit(stackMap->header.numMappedWords -
+                                stackMap->header.frameOffsetFromTop + i) == 0);
+  }
+#endif
+
+  *result = stackMap;
+  return true;
+}
+
+bool wasm::GenerateStackmapEntriesForTrapExit(
+    const ArgTypeVector& args, const RegisterOffsets& trapExitLayout,
+    const size_t trapExitLayoutNumWords, ExitStubMapVector* extras) {
+  MOZ_ASSERT(extras->empty());
+
+  if (!extras->appendN(false, trapExitLayoutNumWords)) {
+    return false;
+  }
+
+  for (WasmABIArgIter i(args); !i.done(); i++) {
+    if (!i->argInRegister() || i.mirType() != MIRType::RefOrNull) {
+      continue;
+    }
+
+    size_t offsetFromTop = trapExitLayout.getOffset(i->gpr());
+
+    // If this doesn't hold, the associated register wasn't saved by
+    // the trap exit stub.  Better to crash now than much later, in
+    // some obscure place, and possibly with security consequences.
+    MOZ_RELEASE_ASSERT(offsetFromTop < trapExitLayoutNumWords);
+
+    // offsetFromTop is an offset in words down from the highest
+    // address in the exit stub save area.  Switch it around to be an
+    // offset up from the bottom of the (integer register) save area.
+    size_t offsetFromBottom = trapExitLayoutNumWords - 1 - offsetFromTop;
+
+    (*extras)[offsetFromBottom] = true;
+  }
+
+  return true;
+}
+
+void wasm::EmitWasmPreBarrierGuard(MacroAssembler& masm, Register instance,
+                                   Register scratch, Register valueAddr,
+                                   size_t valueOffset, Label* skipBarrier,
+                                   BytecodeOffset* trapOffset) {
+  // If no incremental GC has started, we don't need the barrier.
+  masm.loadPtr(
+      Address(instance, Instance::offsetOfAddressOfNeedsIncrementalBarrier()),
+      scratch);
+  masm.branchTest32(Assembler::Zero, Address(scratch, 0), Imm32(0x1),
+                    skipBarrier);
+
+  // Emit metadata for a potential null access when reading the previous value.
+  if (trapOffset) {
+    masm.append(wasm::Trap::NullPointerDereference,
+                wasm::TrapSite(masm.currentOffset(), *trapOffset));
+  }
+
+  // If the previous value is null, we don't need the barrier.
+  masm.loadPtr(Address(valueAddr, valueOffset), scratch);
+  masm.branchTestPtr(Assembler::Zero, scratch, scratch, skipBarrier);
+}
+
+void wasm::EmitWasmPreBarrierCall(MacroAssembler& masm, Register instance,
+                                  Register scratch, Register valueAddr,
+                                  size_t valueOffset) {
+  MOZ_ASSERT(valueAddr == PreBarrierReg);
+
+  // Add the offset to the PreBarrierReg, if any.
+  if (valueOffset != 0) {
+    masm.addPtr(Imm32(valueOffset), valueAddr);
+  }
+
+#if defined(DEBUG) && defined(JS_CODEGEN_ARM64)
+  // The prebarrier assumes that x28 == sp.
+  Label ok;
+  masm.Cmp(sp, vixl::Operand(x28));
+  masm.B(&ok, Assembler::Equal);
+  masm.breakpoint();
+  masm.bind(&ok);
+#endif
+
+  // Load and call the pre-write barrier code. It will preserve all volatile
+  // registers.
+  masm.loadPtr(Address(instance, Instance::offsetOfPreBarrierCode()), scratch);
+  masm.call(scratch);
+
+  // Remove the offset we folded into PreBarrierReg, if any.
+  if (valueOffset != 0) {
+    masm.subPtr(Imm32(valueOffset), valueAddr);
+  }
+}
+
+void wasm::EmitWasmPostBarrierGuard(MacroAssembler& masm,
+                                    const Maybe<Register>& object,
+                                    Register otherScratch, Register setValue,
+                                    Label* skipBarrier) {
+  // If the pointer being stored is null, no barrier.
+  masm.branchTestPtr(Assembler::Zero, setValue, setValue, skipBarrier);
+
+  // If there is a containing object and it is in the nursery, no barrier.
+  if (object) {
+    masm.branchPtrInNurseryChunk(Assembler::Equal, *object, otherScratch,
+                                 skipBarrier);
+  }
+
+  // If the pointer being stored is to a tenured object, no barrier.
+  masm.branchPtrInNurseryChunk(Assembler::NotEqual, setValue, otherScratch,
+                               skipBarrier);
+}
+
+#ifdef DEBUG
+bool wasm::IsValidStackMapKey(bool debugEnabled, const uint8_t* nextPC) {
+#  if defined(JS_CODEGEN_X64) || defined(JS_CODEGEN_X86)
+  const uint8_t* insn = nextPC;
+  return (insn[-2] == 0x0F && insn[-1] == 0x0B) ||           // ud2
+         (insn[-2] == 0xFF && (insn[-1] & 0xF8) == 0xD0) ||  // call *%r_
+         insn[-5] == 0xE8;                                   // call simm32
+
+#  elif defined(JS_CODEGEN_ARM)
+  const uint32_t* insn = (const uint32_t*)nextPC;
+  return ((uintptr_t(insn) & 3) == 0) &&            // must be ARM, not Thumb
+         (insn[-1] == 0xe7f000f0 ||                 // udf
+          (insn[-1] & 0xfffffff0) == 0xe12fff30 ||  // blx reg (ARM, enc A1)
+          (insn[-1] & 0x0f000000) == 0x0b000000);   // bl.cc simm24 (ARM, enc A1)
+
+#  elif defined(JS_CODEGEN_ARM64)
+  const uint32_t hltInsn = 0xd4a00000;
+  const uint32_t* insn = (const uint32_t*)nextPC;
+  return ((uintptr_t(insn) & 3) == 0) &&
+         (insn[-1] == hltInsn ||                    // hlt
+          (insn[-1] & 0xfffffc1f) == 0xd63f0000 ||  // blr reg
+          (insn[-1] & 0xfc000000) == 0x94000000);   // bl simm26
+
+#  elif defined(JS_CODEGEN_MIPS64)
+  // TODO (bug 1699696): Implement this.  As for the platforms above, we need to
+  // enumerate all code sequences that can precede the stackmap location.
+  return true;
+#  elif defined(JS_CODEGEN_LOONG64)
+  // TODO(loong64): Implement IsValidStackMapKey.
+  return true;
+#  elif defined(JS_CODEGEN_RISCV64)
+  const uint32_t* insn = (const uint32_t*)nextPC;
+  return (((uintptr_t(insn) & 3) == 0) &&
+              (insn[-1] == 0x00006037 && insn[-2] == 0x00100073) ||  // break;
+          ((insn[-1] & kBaseOpcodeMask) == JALR));
+#  else
+  MOZ_CRASH("IsValidStackMapKey: requires implementation on this platform");
+#  endif
+}
+#endif