Skip JS shared memory tests on build configs that don't have it

Drive-by fix to align what builds the test runner considers to be able
to have shared memory features and what builds can create a shared
Isolate.

Bug: v8:12007
Change-Id: I151513ccbfbee31e5b35c5ce8e9192732eabfee2
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3421507
Reviewed-by: Adam Klein <adamk@chromium.org>
Commit-Queue: Shu-yu Guo <syg@chromium.org>
Cr-Commit-Position: refs/heads/main@{#78824}

BUILD.gn

@@ -2218,6 +2218,7 @@ action("v8_dump_build_config") {
     "v8_enable_pointer_compression_shared_cage=" +
         "$v8_enable_pointer_compression_shared_cage",
     "v8_enable_sandbox=$v8_enable_sandbox",
+    "v8_enable_shared_ro_heap=$v8_enable_shared_ro_heap",
     "v8_enable_third_party_heap=$v8_enable_third_party_heap",
     "v8_enable_webassembly=$v8_enable_webassembly",
     "v8_dict_property_const_tracking=$v8_dict_property_const_tracking",

src/execution/isolate.cc

@@ -3211,17 +3211,19 @@ Isolate::Isolate(std::unique_ptr<i::IsolateAllocator> isolate_allocator,
 
   handle_scope_data_.Initialize();
 
-  // When pointer compression is on with a per-Isolate cage, allocation in the
-  // shared Isolate can point into the per-Isolate RO heap as the offsets are
-  // constant across Isolates.
+  // A shared Isolate is used to support JavaScript shared memory features
+  // across Isolates. These features require all of the following to hold in the
+  // build configuration:
   //
-  // When pointer compression is on with a shared cage or when pointer
-  // compression is off, a shared RO heap is required. Otherwise a shared
-  // allocation requested by a client Isolate could point into the client
-  // Isolate's RO space (e.g. an RO map) whose pages gets unmapped when it is
-  // disposed.
-  CHECK_IMPLIES(is_shared_, COMPRESS_POINTERS_IN_ISOLATE_CAGE_BOOL ||
-                                V8_SHARED_RO_HEAP_BOOL);
+  // 1. The RO space is shared, so e.g. immortal RO maps can be shared across
+  //   Isolates.
+  // 2. HeapObjects are shareable across Isolates, which requires either
+  //   pointers to be uncompressed (!COMPRESS_POINTER_BOOL), or that there is a
+  //   single virtual memory reservation shared by all Isolates in the process
+  //   for compressing pointers (COMPRESS_POINTERS_IN_SHARED_CAGE_BOOL).
+  CHECK_IMPLIES(is_shared_, V8_SHARED_RO_HEAP_BOOL &&
+                                (!COMPRESS_POINTERS_BOOL ||
+                                 COMPRESS_POINTERS_IN_SHARED_CAGE_BOOL));
 
 #define ISOLATE_INIT_EXECUTE(type, name, initial_value) \
   name##_ = (initial_value);

test/mjsunit/mjsunit.status

@@ -1801,4 +1801,9 @@
   'tzoffset-transition-moscow': [FAIL],
 }], # variant == google3_nociu
 
+# Tests that cannot run without JS shared memory
+['no_js_shared_memory', {
+  'shared-memory/*': [SKIP],
+}],  # 'no_js_shared_memory'
+
 ]

tools/testrunner/base_runner.py

@@ -192,6 +192,7 @@ class BuildConfig(object):
     self.lite_mode = build_config['v8_enable_lite_mode']
     self.pointer_compression = build_config['v8_enable_pointer_compression']
     self.pointer_compression_shared_cage = build_config['v8_enable_pointer_compression_shared_cage']
+    self.shared_ro_heap = build_config['v8_enable_shared_ro_heap']
     self.sandbox = build_config['v8_enable_sandbox']
     self.third_party_heap = build_config['v8_enable_third_party_heap']
     self.webassembly = build_config['v8_enable_webassembly']
@@ -732,6 +733,9 @@ class BaseTestRunner(object):
       "lite_mode": self.build_config.lite_mode,
       "pointer_compression": self.build_config.pointer_compression,
       "pointer_compression_shared_cage": self.build_config.pointer_compression_shared_cage,
+      "no_js_shared_memory": (not self.build_config.shared_ro_heap) or
+                             (self.build_config.pointer_compression and
+                              not self.build_config.pointer_compression_shared_cage),
       "sandbox": self.build_config.sandbox,
       "dict_property_const_tracking": self.build_config.dict_property_const_tracking,
     }

tools/unittests/run_tests_test.py

@@ -351,6 +351,7 @@ class SystemTest(unittest.TestCase):
           v8_enable_verify_csa=False, v8_enable_lite_mode=False,
           v8_enable_pointer_compression=False,
           v8_enable_pointer_compression_shared_cage=False,
+          v8_enable_shared_ro_heap=False,
           v8_enable_sandbox=False)
       result = run_tests(
           basedir,

tools/unittests/testdata/testroot1/v8_build_config.json

@@ -23,6 +23,7 @@
   "v8_enable_pointer_compression": true,
   "v8_enable_pointer_compression_shared_cage": true,
   "v8_enable_sandbox": false,
+  "v8_enable_shared_ro_heap": true,
   "v8_control_flow_integrity": false,
   "v8_enable_single_generation": false,
   "v8_enable_third_party_heap": false,

tools/unittests/testdata/testroot2/v8_build_config.json

@@ -23,6 +23,7 @@
   "v8_enable_pointer_compression": false,
   "v8_enable_pointer_compression_shared_cage": false,
   "v8_enable_sandbox": false,
+  "v8_enable_shared_ro_heap": false,
   "v8_control_flow_integrity": false,
   "v8_enable_single_generation": false,
   "v8_enable_third_party_heap": false,

tools/unittests/testdata/testroot3/v8_build_config.json

@@ -23,6 +23,7 @@
   "v8_enable_pointer_compression": true,
   "v8_enable_pointer_compression_shared_cage": true,
   "v8_enable_sandbox": false,
+  "v8_enable_shared_ro_heap": true,
   "v8_control_flow_integrity": false,
   "v8_enable_single_generation": false,
   "v8_enable_third_party_heap": false,