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8361342: Shenandoah: Evacuation may assert on invalid mirror object after JDK-8340297 #26187

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8361342: Shenandoah: Evacuation may assert on invalid mirror object after JDK-8340297 #26187

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a9c3c58
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tstuefe Jul 8, 2025
3d07a9d
also fix ShenandoahVerifier
tstuefe Jul 8, 2025
e8d7c5a
Merge branch 'master' into JDK-8361342-Sheandoah-evacuation-asserts-o…
tstuefe Jul 9, 2025
4d23ef7
Merge branch 'master' into JDK-8361342-Sheandoah-evacuation-asserts-o…
tstuefe Jul 9, 2025
fba14a0
Also check array klass
tstuefe Jul 9, 2025
c33cf24
Alekseys additions
tstuefe Jul 10, 2025
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16 changes: 11 additions & 5 deletions src/hotspot/share/gc/shenandoah/shenandoahAsserts.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -77,6 +77,10 @@ void ShenandoahAsserts::print_obj(ShenandoahMessageBuffer& msg, oop obj) {
}
msg.append(" mark:%s\n", mw_ss.freeze());
msg.append(" region: %s", ss.freeze());
if (obj_klass == vmClasses::Class_klass()) {
msg.append(" mirrored klass: " PTR_FORMAT "\n", p2i(obj->metadata_field(java_lang_Class::klass_offset())));
msg.append(" mirrored array klass: " PTR_FORMAT "\n", p2i(obj->metadata_field(java_lang_Class::array_klass_offset())));
}
}

void ShenandoahAsserts::print_non_obj(ShenandoahMessageBuffer& msg, void* loc) {
Expand Down Expand Up @@ -268,20 +272,22 @@ void ShenandoahAsserts::assert_correct(void* interior_loc, oop obj, const char*
}

// Do additional checks for special objects: their fields can hold metadata as well.
// We want to check class loading/unloading did not corrupt them.
// We want to check class loading/unloading did not corrupt them. We can only reasonably
// trust the forwarded objects, as the from-space object can have the klasses effectively
// dead.

if (Universe::is_fully_initialized() && (obj_klass == vmClasses::Class_klass())) {
Metadata* klass = obj->metadata_field(java_lang_Class::klass_offset());
const Metadata* klass = fwd->metadata_field(java_lang_Class::klass_offset());
if (klass != nullptr && !Metaspace::contains(klass)) {
print_failure(_safe_all, obj, interior_loc, nullptr, "Shenandoah assert_correct failed",
"Instance class mirror should point to Metaspace",
"Mirrored instance class should point to Metaspace",
file, line);
}

Metadata* array_klass = obj->metadata_field(java_lang_Class::array_klass_offset());
const Metadata* array_klass = fwd->metadata_field(java_lang_Class::array_klass_offset());
if (array_klass != nullptr && !Metaspace::contains(array_klass)) {
print_failure(_safe_all, obj, interior_loc, nullptr, "Shenandoah assert_correct failed",
"Array class mirror should point to Metaspace",
"Mirrored array class should point to Metaspace",
file, line);
}
}
Expand Down
12 changes: 7 additions & 5 deletions src/hotspot/share/gc/shenandoah/shenandoahVerifier.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -244,18 +244,20 @@ class ShenandoahVerifyOopClosure : public BasicOopIterateClosure {
}

// Do additional checks for special objects: their fields can hold metadata as well.
// We want to check class loading/unloading did not corrupt them.
// We want to check class loading/unloading did not corrupt them. We can only reasonably
// trust the forwarded objects, as the from-space object can have the klasses effectively
// dead.

if (obj_klass == vmClasses::Class_klass()) {
Metadata* klass = obj->metadata_field(java_lang_Class::klass_offset());
const Metadata* klass = fwd->metadata_field(java_lang_Class::klass_offset());
check(ShenandoahAsserts::_safe_oop, obj,
klass == nullptr || Metaspace::contains(klass),
"Instance class mirror should point to Metaspace");
"Mirrored instance class should point to Metaspace");

Metadata* array_klass = obj->metadata_field(java_lang_Class::array_klass_offset());
const Metadata* array_klass = obj->metadata_field(java_lang_Class::array_klass_offset());
check(ShenandoahAsserts::_safe_oop, obj,
array_klass == nullptr || Metaspace::contains(array_klass),
"Array class mirror should point to Metaspace");
"Mirrored array class should point to Metaspace");
}

// ------------ obj and fwd are safe at this point --------------
Expand Down