[nojit] Expose wasm in jitless mode for correctness fuzzers

Correctness fuzzers need the global object to have a consistent shape
across build configs.

Bug: chromium:932877,chromium:932656,v8:7777
Change-Id: Id4e1251e50965b822bc4ef36c5ae2777864273d5
Reviewed-on: https://chromium-review.googlesource.com/c/1475768Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59654}

src/flag-definitions.h

@@ -1052,6 +1052,7 @@ DEFINE_BOOL(stack_trace_on_illegal, false,
             "print stack trace when an illegal exception is thrown")
 DEFINE_BOOL(abort_on_uncaught_exception, false,
             "abort program (dump core) when an uncaught exception is thrown")
+// TODO(jgruber,machenbach): Rename to --correctness-fuzzer-suppressions.
 DEFINE_BOOL(abort_on_stack_or_string_length_overflow, false,
             "Abort program when the stack overflows or a string exceeds "
             "maximum length (as opposed to throwing RangeError). This is "
@@ -1178,10 +1179,7 @@ DEFINE_NEG_IMPLICATION(jitless, validate_asm)
 DEFINE_IMPLICATION(jitless, wasm_interpret_all)
 DEFINE_NEG_IMPLICATION(jitless, asm_wasm_lazy_compilation)
 DEFINE_NEG_IMPLICATION(jitless, wasm_lazy_compilation)
-// Even in interpreter-only mode, wasm currently still creates executable
-// memory at runtime. Disable until this changes.
-// TODO(jgruber): Remove this once / if wasm can run without executable memory.
-DEFINE_NEG_IMPLICATION(jitless, expose_wasm)
+// --jitless also implies --no-expose-wasm, see InitializeOncePerProcessImpl.
 
 // Enable recompilation of function with optimized code.
 DEFINE_BOOL(opt, !V8_LITE_BOOL, "use adaptive optimizations")

src/v8.cc

@@ -78,6 +78,20 @@ void V8::InitializeOncePerProcessImpl() {
                   std::ios_base::trunc);
   }
 
+  // Do not expose wasm in jitless mode.
+  //
+  // Even in interpreter-only mode, wasm currently still creates executable
+  // memory at runtime. Unexpose wasm until this changes.
+  // The correctness fuzzers are a special case: many of their test cases are
+  // built by fetching a random property from the the global object, and thus
+  // the global object layout must not change between configs. That is why we
+  // continue exposing wasm on correctness fuzzers even in jitless mode.
+  // TODO(jgruber): Remove this once / if wasm can run without executable
+  // memory.
+  if (FLAG_jitless && !FLAG_abort_on_stack_or_string_length_overflow) {
+    FLAG_expose_wasm = false;
+  }
+
   base::OS::Initialize(FLAG_hard_abort, FLAG_gc_fake_mmap);
 
   if (FLAG_random_seed) SetRandomMmapSeed(FLAG_random_seed);