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[snapshot] Re-enable shared read-only heap with --stress-snapshot

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Disable the checksum comparison for the read-only snapshot when
--stress-snapshot is used, since it's possible that it would be
corrupted. This corruption is not important as the purpose of
stress-snapshot is not to produce a useable snapshot, but to test that
the serialization/deserialization does not fail for any given objects.

Since the --stress-snapshot flag's value is now used outside of d8,
this also moves it to flag-definitions.h.

Cq-Include-Trybots: luci.v8.try:v8_linux64_gc_stress_custom_snapshot_dbg_ng
Bug: v8:11750
Change-Id: Iedcf1cfb5afa5f16ac19a76820b62b5b93948f2c
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2882810
Commit-Queue: Dan Elphick <delphick@chromium.org>
Auto-Submit: Dan Elphick <delphick@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Marja Hölttä <marja@chromium.org>
Cr-Commit-Position: refs/heads/master@{#74480}
This commit is contained in:
Dan Elphick 2021-05-10 15:52:57 +01:00 committed by V8 LUCI CQ
parent e1ce9f40dd
commit f4a6c628c9
4 changed files with 24 additions and 22 deletions
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21
src/d8/d8.cc
View File

@ -3971,25 +3971,6 @@ bool Shell::SetOptions(int argc, char* argv[]) {
strcmp(argv[i], "--no-stress-opt") == 0) {
options.stress_opt = false;
argv[i] = nullptr;
} else if (strcmp(argv[i], "--stress-snapshot") == 0) {
options.stress_snapshot = true;
// Incremental marking is incompatible with the stress_snapshot mode;
// specifically, serialization may clear bytecode arrays from shared
// function infos which the MarkCompactCollector (running concurrently)
// may still need. See also https://crbug.com/v8/10882.
//
// We thus force the implication
//
// --stress-snapshot ~~> --no-incremental-marking
//
// Note: This is not an issue in production because we don't clear SFI's
// there (that only happens in mksnapshot and in --stress-snapshot mode).
i::FLAG_incremental_marking = false;
argv[i] = nullptr;
} else if (strcmp(argv[i], "--nostress-snapshot") == 0 ||
strcmp(argv[i], "--no-stress-snapshot") == 0) {
options.stress_snapshot = false;
argv[i] = nullptr;
} else if (strcmp(argv[i], "--noalways-opt") == 0 ||
strcmp(argv[i], "--no-always-opt") == 0) {
no_always_opt = true;
@ -4244,7 +4225,7 @@ int Shell::RunMain(Isolate* isolate, bool last_run) {
DisposeModuleEmbedderData(context);
}
WriteLcovData(isolate, options.lcov_file);
if (last_run && options.stress_snapshot) {
if (last_run && i::FLAG_stress_snapshot) {
static constexpr bool kClearRecompilableData = true;
i::Isolate* i_isolate = reinterpret_cast<i::Isolate*>(isolate);
i::Handle<i::Context> i_context = Utils::OpenHandle(*context);

1
src/d8/d8.h
View File

@ -362,7 +362,6 @@ class ShellOptions {
DisallowReassignment<bool> simulate_errors = {"simulate-errors", false};
DisallowReassignment<bool> stress_opt = {"stress-opt", false};
DisallowReassignment<int> stress_runs = {"stress-runs", 1};
DisallowReassignment<bool> stress_snapshot = {"stress-snapshot", false};
DisallowReassignment<bool> interactive_shell = {"shell", false};
bool test_shell = false;
DisallowReassignment<bool> expected_to_throw = {"throws", false};

11
src/flags/flag-definitions.h
View File

@ -377,6 +377,17 @@ DEFINE_BOOL(icu_timezone_data, true, "get information about timezones from ICU")
#define V8_SHARED_RO_HEAP_BOOL false
#endif
DEFINE_BOOL(stress_snapshot, false,
"disables sharing of the read-only heap for testing")
// Incremental marking is incompatible with the stress_snapshot mode;
// specifically, serialization may clear bytecode arrays from shared function
// infos which the MarkCompactCollector (running concurrently) may still need.
// See also https://crbug.com/v8/10882.
//
// Note: This is not an issue in production because we don't clear SFI's
// there (that only happens in mksnapshot and in --stress-snapshot mode).
DEFINE_NEG_IMPLICATION(stress_snapshot, incremental_marking)
DEFINE_BOOL(lite_mode, V8_LITE_BOOL,
"enables trade-off of performance for memory savings")

13
src/heap/read-only-spaces.cc
View File

@ -56,7 +56,18 @@ void ReadOnlyArtifacts::VerifyChecksum(SnapshotData* read_only_snapshot_data,
CHECK_WITH_MSG(snapshot_checksum,
"Attempt to create the read-only heap after already "
"creating from a snapshot.");
CHECK_EQ(read_only_blob_checksum_, snapshot_checksum);
if (!FLAG_stress_snapshot) {
// --stress-snapshot is only intended to check how well the
// serializer/deserializer copes with unexpected objects, and is not
// intended to test whether the newly deserialized Isolate would actually
// work since it serializes a currently running Isolate, which is not
// supported. As a result, it's possible that it will create a new
// read-only snapshot that is not compatible with the original one (for
// instance due to the string table being re-ordered). Since we won't
// acutally use that new Isoalte, we're ok with any potential corruption.
// See crbug.com/1043058.
CHECK_EQ(read_only_blob_checksum_, snapshot_checksum);
}
} else {
// If there's no checksum, then that means the read-only heap objects are
// being created.