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LibJVM: Refactor the constant pool into a class
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The constant pool now has its own class ConstantPool.
Also the invidivual constants now have nicer accesors which lookup their
indices in the given constant pool.
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@noahhaasis
noahhaasis committed Dec 30, 2021
1 parent acea722 commit a6cad50
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Showing 4 changed files with 167 additions and 105 deletions.
6 changes: 6 additions & 0 deletions Userland/Libraries/LibJVM/CMakeLists.txt
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@@ -0,0 +1,6 @@
set(SOURCES
ClassFileParser.cpp
)

serenity_lib(LibJVM jvm)
target_link_libraries(LibJVM LibCore)
10 changes: 9 additions & 1 deletion Userland/Libraries/LibJVM/ClassFile.h
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Expand Up @@ -20,27 +20,35 @@ struct AttributeInfo {
u16 attribute_name_index;
u32 attribute_length;
u8 const* info;

ConstantPool::Utf8 attribute_name(ConstantPool const& constant_pool) const { return constant_pool.utf8_at(attribute_name_index); }
};

struct FieldInfo {
u16 access_flags;
u16 name_index;
u16 descriptor_index;
AK::FixedArray<AttributeInfo> attributes;

ConstantPool::Utf8 name(ConstantPool const& constant_pool) const { return constant_pool.utf8_at(name_index); }
ConstantPool::Utf8 descriptor(ConstantPool const& constant_pool) const { return constant_pool.utf8_at(descriptor_index); }
};

struct MethodInfo {
u16 access_flags;
u16 name_index;
u16 descriptor_index;
AK::FixedArray<AttributeInfo> attributes;

ConstantPool::Utf8 name(ConstantPool const& constant_pool) const { return constant_pool.utf8_at(name_index); }
ConstantPool::Utf8 descriptor(ConstantPool const& constant_pool) const { return constant_pool.utf8_at(descriptor_index); }
};

// https://docs.oracle.com/javase/specs/jvms/se7/html/jvms-4.html
struct ClassFile {
u16 minor_version;
u16 major_version;
FixedArray<ConstantPool::Constant> constant_pool;
ConstantPool constant_pool;
u16 access_flags;
ConstantPool::Class this_class;
AK::Optional<ConstantPool::Class> super_class;
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19 changes: 8 additions & 11 deletions Userland/Libraries/LibJVM/ClassFileParser.cpp
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Expand Up @@ -46,9 +46,9 @@ void ClassFileParser::parse_constant_pool()
{
u16 constant_pool_count = read_u16() - 1;

auto constant_pool = FixedArray<ConstantPool::Constant>(constant_pool_count);
m_classfile->constant_pool = constant_pool;
for (auto& constant : m_classfile->constant_pool)
auto constants = FixedArray<ConstantPool::Constant>(constant_pool_count);
m_classfile->constant_pool.set_constants(constants);
for (auto& constant : m_classfile->constant_pool.constants())
constant = parse_constant_info();
}

Expand All @@ -58,8 +58,7 @@ ConstantPool::Constant ClassFileParser::parse_constant_info()
switch (tag) {
case ConstantPool::Constant::Tag::Class: {
ConstantPool::Class class_constant;
[[maybe_unused]] u16 name_index = read_u16() - 1;
// class_constant.name = (Constant const*)(m_classfile->constant_pool.span().offset_pointer(name_index));
class_constant.name_index = read_u16() - 1;
return ConstantPool::Constant(class_constant);
}
case ConstantPool::Constant::Tag::Utf8: {
Expand Down Expand Up @@ -93,22 +92,20 @@ ConstantPool::Constant ClassFileParser::parse_constant_info()

void ClassFileParser::parse_class_references()
{
m_classfile->this_class = (m_classfile->constant_pool.span().offset_pointer(read_u16() - 1))->as_class();
m_classfile->this_class = m_classfile->constant_pool.class_at(read_u16() - 1);
u16 super_class_index = read_u16() - 1;
if (super_class_index == 0)
m_classfile->super_class = {};
else
m_classfile->super_class = m_classfile->constant_pool.span().offset_pointer(super_class_index)->as_class();
m_classfile->super_class = m_classfile->constant_pool.class_at(super_class_index);
}

void ClassFileParser::parse_interfaces()
{
u16 interfaces_count = read_u16();
auto interfaces = FixedArray<ConstantPool::Class>(interfaces_count);
for (auto& interface : interfaces) {
u16 interface_index = read_u16() - 1;
interface = m_classfile->constant_pool.span().offset_pointer(interface_index)->as_class();
}
for (auto& interface : interfaces)
interface = m_classfile->constant_pool.class_at(read_u16() - 1);

m_classfile->interfaces = interfaces;
}
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237 changes: 144 additions & 93 deletions Userland/Libraries/LibJVM/ConstantPool.h
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Expand Up @@ -11,130 +11,181 @@
namespace JVM {

// https://docs.oracle.com/javase/specs/jvms/se7/html/jvms-4.html#jvms-4.4
class ConstantPool {
public:
struct Utf8 {
u32 length;
u8 const* bytes;
};

namespace ConstantPool {

struct Utf8 {
u32 length;
u8 const* bytes;
};

struct Class {
u16 name_and_type_index;
};
struct NameAndType {
u16 name_index;
u16 descriptor_index;

struct Integer {
u32 bytes;
};
Utf8 name(ConstantPool const& constant_pool) const { return constant_pool.utf8_at(name_index); }
Utf8 descriptor(ConstantPool const& constant_pool) const { return constant_pool.utf8_at(descriptor_index); }
};

struct NameAndType {
u16 name_index;
u16 descriptor_index;
};
struct Class {
u16 name_index;

struct Methodref {
u16 class_index;
u16 name_and_type_index;
};
Utf8 name(ConstantPool const& constant_pool) const { return constant_pool.utf8_at(name_index); }
};

class Constant {
public:
enum Tag : u8 {
Class = 7,
Fieldref = 9,
Methodref = 10,
InterfaceMethodref = 11,
String = 8,
Integer = 3,
Float = 4,
Long = 5,
Double = 6,
NameAndType = 12,
Utf8 = 1,
MethodHandle = 15,
MethodType = 16,
Invokedynamic = 18,
struct Integer {
u32 bytes;
};

Constant() {};
struct Methodref {
u16 class_index;
u16 name_and_type_index;

Constant(struct Utf8 value)
: m_tag(Tag::Utf8)
{
m_value.as_utf8 = value;
};
Class class_info(ConstantPool const& constant_pool) const
{
return constant_pool.class_at(class_index);
}

Constant(struct Class value)
: m_tag(Tag::Class)
{
m_value.as_class = value;
NameAndType name_and_type(ConstantPool const& constant_pool) const
{
return constant_pool.name_and_type_at(name_and_type_index);
}
};

Constant(struct Integer value)
: m_tag(Tag::Integer)
{
m_value.as_integer = value;
class Constant {
public:
enum Tag : u8 {
Class = 7,
Fieldref = 9,
Methodref = 10,
InterfaceMethodref = 11,
String = 8,
Integer = 3,
Float = 4,
Long = 5,
Double = 6,
NameAndType = 12,
Utf8 = 1,
MethodHandle = 15,
MethodType = 16,
Invokedynamic = 18,
};

Constant() {};

Constant(struct Utf8 value)
: m_tag(Tag::Utf8)
{
m_value.as_utf8 = value;
};

Constant(struct Class value)
: m_tag(Tag::Class)
{
m_value.as_class = value;
};

Constant(struct Integer value)
: m_tag(Tag::Integer)
{
m_value.as_integer = value;
};

Constant(struct NameAndType value)
: m_tag(Tag::NameAndType)
{
m_value.as_name_and_type = value;
};

Constant(struct Methodref value)
: m_tag(Tag::Methodref)
{
m_value.as_methodref = value;
};

struct Utf8 as_utf8() const
{
VERIFY(is_utf8());
return m_value.as_utf8;
}

struct Class as_class() const
{
VERIFY(is_class());
return m_value.as_class;
}

struct Integer as_integer() const
{
VERIFY(is_integer());
return m_value.as_integer;
}

struct NameAndType as_name_and_type() const
{
VERIFY(is_name_and_type());
return m_value.as_name_and_type;
}

struct Methodref as_methodref() const
{
VERIFY(is_methodref());
return m_value.as_methodref;
}

bool is_utf8() const { return m_tag == Tag::Utf8; }
bool is_class() const { return m_tag == Tag::Class; }
bool is_integer() const { return m_tag == Tag::Integer; }
bool is_name_and_type() const { return m_tag == Tag::NameAndType; }
bool is_methodref() const { return m_tag == Tag::Methodref; }

private:
Tag m_tag;
union {
struct Utf8 as_utf8;
struct Class as_class;
struct Integer as_integer;
struct NameAndType as_name_and_type;
struct Methodref as_methodref;
} m_value;
};

Constant(struct NameAndType value)
: m_tag(Tag::NameAndType)
{
m_value.as_name_and_type = value;
};
ConstantPool() = default;

Constant(struct Methodref value)
: m_tag(Tag::Methodref)
{
m_value.as_methodref = value;
};
FixedArray<Constant>& constants() { return m_constants; }
void set_constants(FixedArray<Constant> constants) { m_constants = constants; }

struct Utf8 as_utf8() const
Utf8 utf8_at(unsigned index) const
{
VERIFY(is_utf8());
return m_value.as_utf8;
VERIFY(index < m_constants.size());
return m_constants[index].as_utf8();
}

struct Class as_class() const
Class class_at(unsigned index) const
{
VERIFY(is_class());
return m_value.as_class;
VERIFY(index < m_constants.size());
return m_constants[index].as_class();
}

struct Integer as_integer() const
Integer integer_at(unsigned index) const
{
VERIFY(is_integer());
return m_value.as_integer;
VERIFY(index < m_constants.size());
return m_constants[index].as_integer();
}

struct NameAndType as_name_and_type() const
NameAndType name_and_type_at(unsigned index) const
{
VERIFY(is_name_and_type());
return m_value.as_name_and_type;
VERIFY(index < m_constants.size());
return m_constants[index].as_name_and_type();
}

struct Methodref as_methodref() const
Methodref methodref_at(unsigned index) const
{
VERIFY(is_methodref());
return m_value.as_methodref;
VERIFY(index < m_constants.size());
return m_constants[index].as_methodref();
}

bool is_utf8() const { return m_tag == Tag::Utf8; }
bool is_class() const { return m_tag == Tag::Class; }
bool is_integer() const { return m_tag == Tag::Integer; }
bool is_name_and_type() const { return m_tag == Tag::NameAndType; }
bool is_methodref() const { return m_tag == Tag::Methodref; }

private:
Tag m_tag;
union {
struct Utf8 as_utf8;
struct Class as_class;
struct Integer as_integer;
struct NameAndType as_name_and_type;
struct Methodref as_methodref;
} m_value;
FixedArray<Constant> m_constants;
};

}

}

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