On Tue, 17 May 2022 12:38:55 GMT, Yasumasa Suenaga <ysuen...@openjdk.org> wrote:
>> src/hotspot/share/classfile/classFileParser.cpp line 5970:
>>
>>> 5968: PRAGMA_STRINGOP_OVERFLOW_IGNORED
>>> 5969: _cp->symbol_at_put(hidden_index, _class_name);
>>> 5970: PRAGMA_DIAG_POP
>>
>> I don't understand these warning suppressions for symbol_at_put (here and
>> elsewhere). I don't see any stringops here. What is the compiler
>> complaining about? (There's no mention of classfile stuff in the review
>> cover message.)
>
> Like the others, it is caused by `Array::at_put()`.
>
>
> In file included from
> /home/ysuenaga/github-forked/jdk/src/hotspot/share/oops/annotations.hpp:28,
> from
> /home/ysuenaga/github-forked/jdk/src/hotspot/share/oops/instanceKlass.hpp:29,
> from
> /home/ysuenaga/github-forked/jdk/src/hotspot/share/classfile/javaClasses.hpp:30,
> from
> /home/ysuenaga/github-forked/jdk/src/hotspot/share/precompiled/precompiled.hpp:35:
> In member function 'void Array<T>::at_put(int, const T&) [with T = unsigned
> char]',
> inlined from 'void ConstantPool::tag_at_put(int, jbyte)' at
> /home/ysuenaga/github-forked/jdk/src/hotspot/share/oops/constantPool.hpp:126:64,
> inlined from 'void ConstantPool::symbol_at_put(int, Symbol*)' at
> /home/ysuenaga/github-forked/jdk/src/hotspot/share/oops/constantPool.hpp:362:15,
> inlined from 'void
> ClassFileParser::mangle_hidden_class_name(InstanceKlass*)' at
> /home/ysuenaga/github-forked/jdk/src/hotspot/share/classfile/classFileParser.cpp:5966:21:
`Array<T>::_data` is a pseudo flexible array member. "Pseudo" because C++
doesn't have flexible array members. The compiler is completely justified in
complaining about the apparently out-of-bounds accesses.
There is a "well-known" (though moderately ugly) approach to doing flexible
array members in C++. Something like this:
T* data() {
return reinterpret_cast<T*>(
reinterpret_cast<char*>(this) + data_offset());
}
where `data_offset()` is new and private:
static size_t data_offset() {
return offset_of(Array, _data);
}
Use `data()` everywhere instead of using `_data` directly.
There are other places in HotSpot that use this kind of approach.
-------------
PR: https://git.openjdk.java.net/jdk/pull/8646
