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8383567: [lworld] VM.class_print_layout should use external class names #2375

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8383567: [lworld] VM.class_print_layout should use external class names #2375

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2bdaa63
change print_class_layout to use external class names
caspernorrbin Apr 29, 2026
c8df796
feedback fixes
caspernorrbin Apr 30, 2026
eb127d3
feedback
caspernorrbin May 4, 2026
6baa184
Merge branch 'lworld' into print_class_layout_external_names
caspernorrbin May 12, 2026
7a18def
indent fix
caspernorrbin May 12, 2026
d1ffe8a
merge miss
caspernorrbin May 12, 2026
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19 changes: 12 additions & 7 deletions src/hotspot/share/memory/heapInspection.cpp
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Original file line number Diff line number Diff line change
@@ -1,5 +1,5 @@
/*
* Copyright (c) 2002, 2025, Oracle and/or its affiliates. All rights reserved.
* Copyright (c) 2002, 2026, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
Expand Down Expand Up @@ -600,12 +600,17 @@ void PrintClassLayout::print_class_layout(outputStream* st, char* class_name) {
return;
}

Thread* THREAD = Thread::current();

Symbol* classname = SymbolTable::probe(class_name, (int)strlen(class_name));
ResourceMark rm;
char* normalized_name = NEW_RESOURCE_ARRAY(char, strlen(class_name) + 1);
strcpy(normalized_name, class_name);
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@dholmes-ora dholmes-ora May 1, 2026

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Do we have to make a copy here rather than modifying in place? The user-supplied string is already in a mutable C-heap allocated buffer, as processed by the DCmd framework. If we think it inappropriate to modify at this level perhaps we can push the conversion up into the DCmd framework itself?

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@fparain fparain May 1, 2026

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There's already a Symbol::as_klass_external_name(char* buf, int size) method to do the '/'s into '.'s conversion. Should this code be moved to a new Symbol::as_klass_internal_name(char* buf, int size) method?

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@caspernorrbin caspernorrbin May 4, 2026

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I kept it in the same location as of now, but removed the extra allocation. I don't think putting it in Symbol is the right place, because here we are just modifying a mutable char*. So the operation is not really on a symbol. But it could perhaps be moved to where we parse the DCmd instead, if you feel like it doesn't belong here.

for (char* p = normalized_name; *p != '\0'; p++) {
if (*p == '.') {
*p = '/';
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@dholmes-ora dholmes-ora May 1, 2026

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This should use JVM_SIGNATURE_DOT and JVM_SIGNATURE_SLASH - though it makes me cringe that we have to do this ad-hoc conversion.

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@caspernorrbin caspernorrbin May 4, 2026

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I didn't know these existed, but I swapped to use these now.

}
}
Symbol* classname = SymbolTable::probe(normalized_name, (int)strlen(normalized_name));

GrowableArray<Klass*>* klasses = new (mtServiceability) GrowableArray<Klass*>(100, mtServiceability);

FindClassByNameClosure fbnc(klasses, classname);
cit.iterate(&fbnc);

Expand All @@ -614,9 +619,9 @@ void PrintClassLayout::print_class_layout(outputStream* st, char* class_name) {
if (!klass->is_instance_klass()) continue; // Skip
InstanceKlass* ik = InstanceKlass::cast(klass);
int tab = 1;
st->print_cr("Class %s [@%s]:", klass->name()->as_C_string(),
klass->class_loader_data()->loader_name());
ResourceMark rm;
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@dholmes-ora dholmes-ora Apr 30, 2026

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You may still need this to limit the ResourceArea usage, otherwise you will be keeping all allocations from the complete loop alive.

st->print_cr("Class %s [@%s]:", klass->external_name(),
klass->class_loader_data()->loader_name());
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GrowableArray<FieldDesc>* fields = new (mtServiceability) GrowableArray<FieldDesc>(100, mtServiceability);
for (AllFieldStream fd(ik); !fd.done(); fd.next()) {
if (!fd.access_flags().is_static()) {
Expand Down
8 changes: 4 additions & 4 deletions test/hotspot/jtreg/runtime/valhalla/inlinetypes/ClassPrintLayoutDcmd.java
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Expand Up @@ -81,10 +81,10 @@ static void testCmd(String arg, int expectExitCode, String... expectStrings) thr
}

public static void main(String args[]) throws Exception {
testCmd("foo/bar", 0, "");
testCmd("foo.bar", 0, "");
testCmd("", 1, "IllegalArgumentException", "mandatory");
testCmd("java/lang/Object", 0, "java/lang/Object", "@bootstrap");
testCmd("java/lang/Class", 0, "java/lang/Class", "@bootstrap");
testCmd("runtime/valhalla/inlinetypes/ClassPrintLayoutDcmd$Line", 0, "@app", "p1", "p2");
testCmd("java.lang.Object", 0, "java.lang.Object", "@bootstrap");
testCmd("java.lang.Class", 0, "java.lang.Class", "@bootstrap");
testCmd("runtime.valhalla.inlinetypes.ClassPrintLayoutDcmd$Line", 0, "@app", "p1", "p2");
}
}