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8269838: BasicTypeDataBase.findDynamicTypeForAddress(addr, basetype) can be simplified

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Reviewed-by: kevinw, sspitsyn
This commit is contained in:
Chris Plummer 2021-12-15 17:08:44 +00:00
parent 1f1db838ab
commit 7517c85da3
1 changed files with 8 additions and 36 deletions
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44
src/jdk.hotspot.agent/share/classes/sun/jvm/hotspot/types/basic/BasicTypeDataBase.java
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@ -175,7 +175,7 @@ public class BasicTypeDataBase implements TypeDataBase {
}
// This implementation should be suitably platform-independent; we
// search nearby memory for the vtbl value of the given type.
// search the first word for the vtbl value of the given type.
Address vtblAddr = vtblForType(type);
@ -231,12 +231,9 @@ public class BasicTypeDataBase implements TypeDataBase {
// switch to this logic but in the interests of stability it will
// be separate for the moment.
// Assuming that the base type is truly the first polymorphic type
// then the vtbl for all subclasss should be at several defined
// locations so only those locations will be checked. It's also
// required that the caller knows that the static type is at least
// baseType. See the notes in guessTypeForAddress for the logic of
// the locations searched.
// Assuming that the base type is truly the first polymorphic type,
// then the vtbl for all subclassses should be in the first word of
// the object.
Address loc1 = addr.getAddressAt(0);
@ -248,50 +245,25 @@ public class BasicTypeDataBase implements TypeDataBase {
}
}
Address loc2 = null;
Address loc3 = null;
long offset2 = baseType.getSize();
// I don't think this should be misaligned under any
// circumstances, but I'm not sure (FIXME: also not sure which
// way to go here, up or down -- assuming down)
offset2 = offset2 - (offset2 % getAddressSize()) - getAddressSize();
if (offset2 > 0) {
loc2 = addr.getAddressAt(offset2);
}
long offset3 = offset2 - getAddressSize();
if (offset3 > 0) {
loc3 = addr.getAddressAt(offset3);
}
Type loc2Match = null;
Type loc3Match = null;
for (Iterator iter = getTypes(); iter.hasNext(); ) {
Type type = (Type) iter.next();
Type superClass = type;
while (superClass != baseType && superClass != null) {
superClass = superClass.getSuperclass();
}
if (superClass == null) continue;
if (superClass == null) continue; // type is not a subclass of baseType
Address vtblAddr = vtblForType(type);
if (vtblAddr == null) {
// This occurs sometimes for intermediate types that are never
// instantiated.
// This occurs sometimes for intermediate types that are never instantiated.
if (DEBUG) {
System.err.println("null vtbl for " + type);
}
continue;
}
// Prefer loc1 match
if (vtblAddr.equals(loc1)) return type;
if (loc2 != null && loc2Match == null && vtblAddr.equals(loc2)) {
loc2Match = type;
}
if (loc3 != null && loc3Match == null && vtblAddr.equals(loc3)) {
loc3Match = type;
if (vtblAddr.equals(loc1)) {
return type;
}
}
if (loc2Match != null) return loc2Match;
if (loc3Match != null) return loc3Match;
return null;
}