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// Copyright 2018 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef V8_WASM_JUMP_TABLE_ASSEMBLER_H_
#define V8_WASM_JUMP_TABLE_ASSEMBLER_H_
#include "src/codegen/macro-assembler.h"
#include "src/wasm/wasm-code-manager.h"
namespace v8 {
namespace internal {
namespace wasm {
// The jump table is the central dispatch point for all (direct and indirect)
// invocations in WebAssembly. It holds one slot per function in a module, with
// each slot containing a dispatch to the currently published {WasmCode} that
// corresponds to the function.
//
// Additionally to this main jump table, there exist special jump tables for
// other purposes:
// - the runtime stub table contains one entry per wasm runtime stub (see
// {WasmCode::RuntimeStubId}, which jumps to the corresponding embedded
// builtin.
// - the lazy compile table contains one entry per wasm function which jumps to
// the common {WasmCompileLazy} builtin and passes the function index that was
// invoked.
//
// The main jump table is split into lines of fixed size, with lines laid out
// consecutively within the executable memory of the {NativeModule}. The slots
// in turn are consecutive within a line, but do not cross line boundaries.
//
// +- L1 -------------------+ +- L2 -------------------+ +- L3 ...
// | S1 | S2 | ... | Sn | x | | S1 | S2 | ... | Sn | x | | S1 ...
// +------------------------+ +------------------------+ +---- ...
//
// The above illustrates jump table lines {Li} containing slots {Si} with each
// line containing {n} slots and some padding {x} for alignment purposes.
// Other jump tables are just consecutive.
//
// The main jump table will be patched concurrently while other threads execute
// it. The code at the new target might also have been emitted concurrently, so
// we need to ensure that there is proper synchronization between code emission,
// jump table patching and code execution.
// On Intel platforms, this all works out of the box because there is cache
// coherency between i-cache and d-cache.
// On ARM, it is safe because the i-cache flush after code emission executes an
// "ic ivau" (Instruction Cache line Invalidate by Virtual Address to Point of
// Unification), which broadcasts to all cores. A core which sees the jump table
// update thus also sees the new code. Since the other core does not explicitly
// execute an "isb" (Instruction Synchronization Barrier), it might still
// execute the old code afterwards, which is no problem, since that code remains
// available until it is garbage collected. Garbage collection itself is a
// synchronization barrier though.
class V8_EXPORT_PRIVATE JumpTableAssembler : public MacroAssembler {
public:
// Translate an offset into the continuous jump table to a jump table index.
static uint32_t SlotOffsetToIndex(uint32_t slot_offset) {
uint32_t line_index = slot_offset / kJumpTableLineSize;
uint32_t line_offset = slot_offset % kJumpTableLineSize;
DCHECK_EQ(0, line_offset % kJumpTableSlotSize);
return line_index * kJumpTableSlotsPerLine +
line_offset / kJumpTableSlotSize;
}
// Translate a jump table index to an offset into the continuous jump table.
static uint32_t JumpSlotIndexToOffset(uint32_t slot_index) {
uint32_t line_index = slot_index / kJumpTableSlotsPerLine;
uint32_t line_offset =
(slot_index % kJumpTableSlotsPerLine) * kJumpTableSlotSize;
return line_index * kJumpTableLineSize + line_offset;
}
// Determine the size of a jump table containing the given number of slots.
static constexpr uint32_t SizeForNumberOfSlots(uint32_t slot_count) {
// TODO(wasm): Once the {RoundUp} utility handles non-powers of two values,
// use: {RoundUp<kJumpTableSlotsPerLine>(slot_count) * kJumpTableLineSize}
return ((slot_count + kJumpTableSlotsPerLine - 1) /
kJumpTableSlotsPerLine) *
kJumpTableLineSize;
}
// Translate a stub slot index to an offset into the continuous jump table.
static uint32_t StubSlotIndexToOffset(uint32_t slot_index) {
return slot_index * kJumpTableStubSlotSize;
}
// Translate a slot index to an offset into the lazy compile table.
static uint32_t LazyCompileSlotIndexToOffset(uint32_t slot_index) {
return slot_index * kLazyCompileTableSlotSize;
}
// Determine the size of a jump table containing only runtime stub slots.
static constexpr uint32_t SizeForNumberOfStubSlots(uint32_t slot_count) {
return slot_count * kJumpTableStubSlotSize;
}
// Determine the size of a lazy compile table.
static constexpr uint32_t SizeForNumberOfLazyFunctions(uint32_t slot_count) {
return slot_count * kLazyCompileTableSlotSize;
}
static void GenerateLazyCompileTable(Address base, uint32_t num_slots,
uint32_t num_imported_functions,
Address wasm_compile_lazy_target) {
uint32_t lazy_compile_table_size = num_slots * kLazyCompileTableSlotSize;
// Assume enough space, so the Assembler does not try to grow the buffer.
JumpTableAssembler jtasm(base, lazy_compile_table_size + 256);
for (uint32_t slot_index = 0; slot_index < num_slots; ++slot_index) {
DCHECK_EQ(slot_index * kLazyCompileTableSlotSize, jtasm.pc_offset());
jtasm.EmitLazyCompileJumpSlot(slot_index + num_imported_functions,
wasm_compile_lazy_target);
}
DCHECK_EQ(lazy_compile_table_size, jtasm.pc_offset());
FlushInstructionCache(base, lazy_compile_table_size);
}
static void GenerateRuntimeStubTable(Address base, Address* targets,
int num_stubs) {
uint32_t table_size = num_stubs * kJumpTableStubSlotSize;
// Assume enough space, so the Assembler does not try to grow the buffer.
JumpTableAssembler jtasm(base, table_size + 256);
int offset = 0;
for (int index = 0; index < num_stubs; ++index) {
DCHECK_EQ(offset, StubSlotIndexToOffset(index));
DCHECK_EQ(offset, jtasm.pc_offset());
jtasm.EmitRuntimeStubSlot(targets[index]);
offset += kJumpTableStubSlotSize;
jtasm.NopBytes(offset - jtasm.pc_offset());
}
FlushInstructionCache(base, table_size);
}
static void PatchJumpTableSlot(Address base, uint32_t slot_index,
Address new_target,
WasmCode::FlushICache flush_i_cache) {
Address slot = base + JumpSlotIndexToOffset(slot_index);
JumpTableAssembler jtasm(slot);
jtasm.EmitJumpSlot(new_target);
jtasm.NopBytes(kJumpTableSlotSize - jtasm.pc_offset());
if (flush_i_cache) {
FlushInstructionCache(slot, kJumpTableSlotSize);
}
}
private:
// Instantiate a {JumpTableAssembler} for patching.
explicit JumpTableAssembler(Address slot_addr, int size = 256)
: MacroAssembler(nullptr, JumpTableAssemblerOptions(),
CodeObjectRequired::kNo,
ExternalAssemblerBuffer(
reinterpret_cast<uint8_t*>(slot_addr), size)) {}
// To allow concurrent patching of the jump table entries, we need to ensure
// that the instruction containing the call target does not cross cache-line
// boundaries. The jump table line size has been chosen to satisfy this.
#if V8_TARGET_ARCH_X64
static constexpr int kJumpTableLineSize = 64;
static constexpr int kJumpTableSlotSize = 5;
static constexpr int kLazyCompileTableSlotSize = 10;
static constexpr int kJumpTableStubSlotSize = 18;
#elif V8_TARGET_ARCH_IA32
static constexpr int kJumpTableLineSize = 64;
static constexpr int kJumpTableSlotSize = 5;
static constexpr int kLazyCompileTableSlotSize = 10;
static constexpr int kJumpTableStubSlotSize = 10;
#elif V8_TARGET_ARCH_ARM
static constexpr int kJumpTableLineSize = 3 * kInstrSize;
static constexpr int kJumpTableSlotSize = 3 * kInstrSize;
static constexpr int kLazyCompileTableSlotSize = 5 * kInstrSize;
static constexpr int kJumpTableStubSlotSize = 5 * kInstrSize;
#elif V8_TARGET_ARCH_ARM64
static constexpr int kJumpTableLineSize = 1 * kInstrSize;
static constexpr int kJumpTableSlotSize = 1 * kInstrSize;
static constexpr int kLazyCompileTableSlotSize = 3 * kInstrSize;
static constexpr int kJumpTableStubSlotSize = 6 * kInstrSize;
#elif V8_TARGET_ARCH_S390X
static constexpr int kJumpTableLineSize = 128;
static constexpr int kJumpTableSlotSize = 14;
static constexpr int kLazyCompileTableSlotSize = 20;
static constexpr int kJumpTableStubSlotSize = 14;
#elif V8_TARGET_ARCH_PPC64
static constexpr int kJumpTableLineSize = 64;
static constexpr int kJumpTableSlotSize = 7 * kInstrSize;
static constexpr int kLazyCompileTableSlotSize = 12 * kInstrSize;
static constexpr int kJumpTableStubSlotSize = 7 * kInstrSize;
#elif V8_TARGET_ARCH_MIPS
static constexpr int kJumpTableLineSize = 6 * kInstrSize;
static constexpr int kJumpTableSlotSize = 4 * kInstrSize;
static constexpr int kLazyCompileTableSlotSize = 6 * kInstrSize;
static constexpr int kJumpTableStubSlotSize = 4 * kInstrSize;
#elif V8_TARGET_ARCH_MIPS64
static constexpr int kJumpTableLineSize = 8 * kInstrSize;
static constexpr int kJumpTableSlotSize = 6 * kInstrSize;
static constexpr int kLazyCompileTableSlotSize = 8 * kInstrSize;
static constexpr int kJumpTableStubSlotSize = 6 * kInstrSize;
#else
static constexpr int kJumpTableLineSize = 1;
static constexpr int kJumpTableSlotSize = 1;
static constexpr int kLazyCompileTableSlotSize = 1;
static constexpr int kJumpTableStubSlotSize = 1;
#endif
static constexpr int kJumpTableSlotsPerLine =
kJumpTableLineSize / kJumpTableSlotSize;
STATIC_ASSERT(kJumpTableSlotsPerLine >= 1);
// {JumpTableAssembler} is never used during snapshot generation, and its code
// must be independent of the code range of any isolate anyway. Just ensure
// that no relocation information is recorded, there is no buffer to store it
// since it is instantiated in patching mode in existing code directly.
static AssemblerOptions JumpTableAssemblerOptions() {
AssemblerOptions options;
options.disable_reloc_info_for_patching = true;
return options;
}
void EmitLazyCompileJumpSlot(uint32_t func_index,
Address lazy_compile_target);
void EmitRuntimeStubSlot(Address builtin_target);
void EmitJumpSlot(Address target);
void NopBytes(int bytes);
};
} // namespace wasm
} // namespace internal
} // namespace v8
#endif // V8_WASM_JUMP_TABLE_ASSEMBLER_H_