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[liftoff] Avoid unneeded protected instruction information

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For static OOB accesses in Liftoff we were adding a protected
instruction information, mapping the PC of a jump instruction to the
landing pad. This is not needed, as the jump instruction is not supposed
to trigger a signal.
This CL slightly refactors the code to avoid this protected instruction
information, and resolves the old TODO.

R=ahaas@chromium.org

Change-Id: I668f3ec6a0815af83cbc04fb307744000166fb8e
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3003156
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#75554}
This commit is contained in:
Clemens Backes 2021-07-05 12:19:26 +02:00 committed by V8 LUCI CQ
parent ce08dec035
commit 13d9ccfcf2
1 changed files with 12 additions and 8 deletions
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20
src/wasm/baseline/liftoff-compiler.cc
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@ -858,10 +858,14 @@ class LiftoffCompiler {
(std::string("out of line: ") + GetRuntimeStubName(ool->stub)).c_str());
__ bind(ool->label.get());
const bool is_stack_check = ool->stub == WasmCode::kWasmStackGuard;
const bool is_mem_out_of_bounds =
ool->stub == WasmCode::kThrowWasmTrapMemOutOfBounds;
if (is_mem_out_of_bounds && env_->use_trap_handler) {
// Only memory OOB traps need a {pc}, but not unconditionally. Static OOB
// accesses do not need protected instruction information, hence they also
// do not set {pc}.
DCHECK_IMPLIES(ool->stub != WasmCode::kThrowWasmTrapMemOutOfBounds,
ool->pc == 0);
if (env_->use_trap_handler && ool->pc != 0) {
uint32_t pc = static_cast<uint32_t>(__ pc_offset());
DCHECK_EQ(pc, __ pc_offset());
protected_instructions_.emplace_back(
@ -2609,6 +2613,8 @@ class LiftoffCompiler {
Label* AddOutOfLineTrap(FullDecoder* decoder, WasmCode::RuntimeStubId stub,
uint32_t pc = 0) {
// Only memory OOB traps need a {pc}.
DCHECK_IMPLIES(stub != WasmCode::kThrowWasmTrapMemOutOfBounds, pc == 0);
DCHECK(FLAG_wasm_bounds_checks);
OutOfLineSafepointInfo* safepoint_info = nullptr;
if (V8_UNLIKELY(for_debugging_)) {
@ -2658,12 +2664,10 @@ class LiftoffCompiler {
CODE_COMMENT("bounds check memory");
// TODO(wasm): This adds protected instruction information for the jump
// instruction we are about to generate. It would be better to just not add
// protected instruction info when the pc is 0.
// Set {pc} of the OOL code to {0} to avoid generation of protected
// instruction information (see {GenerateOutOfLineCode}.
Label* trap_label =
AddOutOfLineTrap(decoder, WasmCode::kThrowWasmTrapMemOutOfBounds,
env_->use_trap_handler ? __ pc_offset() : 0);
AddOutOfLineTrap(decoder, WasmCode::kThrowWasmTrapMemOutOfBounds, 0);
if (statically_oob) {
__ emit_jump(trap_label);