On Sun, 9 Feb 2025 19:43:29 GMT, Vladimir Kozlov <[email protected]> wrote:
>> Remove virtual methods from CodeBlob and nmethod to simplify
>> saving/restoring in Leyden AOT cache. It avoids the need to patch hidden
>> VPTR pointer to class's virtual table.
>>
>> Added C++ static asserts to make sure no virtual methods are added in a
>> future.
>>
>> Fixed/cleaned SA code which process CodeBlob and its subclasses. Use
>> `CodeBlob::_kind` field value to determine the type of blob.
>>
>> Tested tier1-5, hs-tier6-rt (for JFR testing), stress, xcomp
>
> Vladimir Kozlov has updated the pull request incrementally with one
> additional commit since the last revision:
>
> Fix Zero and Minimal VM builds
src/hotspot/share/code/codeBlob.cpp line 58:
> 56: #include <type_traits>
> 57:
> 58: // Virtual methods are not allowed in code blobs to simplify caching
> compiled code.
Is it worth considering generating this code plus also some of the existing
code in the header using an iterator template macro? e.g.
#define CODEBLOBS_DO(do_codeblob_abstract, do_codeblob_nonleaf, \
do_codeblob_leaf) \
do_codeblob_abstract(CodeBlob) \
do_codeblob_leaf(nmethod, Nmethod, nmethod) \
do_codeblob_abstract(RuntimeBlob) \
do_codeblob_nonleaf(BufferBlob, Buffer, buffer) \
do_codeblob_leaf(AdapterBlob, Adapter, adapter) \
. . . \
do_codeblob_leaf(RuntimeStub, Runtime_Stub, runtime_stub) \
. . .
The macro arguments to the templates would themselves be macros:
do_codeblob_abstract(classname) // abstract, non-instantiable class
do_codeblob_nonleaf(classname, kindname, accessorname) // instantiable,
subclassable
do_codeblob_leaf(classname, kindname, accessorname) // instantiable,
non-subclassable
Using a template macro like this to generate the code below -- *plus also* some
of the code currently declared piecemeal in the header -- would guarantee all
cases are covered now and will remain so later so when the macro is updated. I
think it would probably also allow case handling code in AOT cache code to be
generated.
So, we would generate the code here as follows
#define EMPTY1(classname)
#define EMPTY3(classname, kindname, accessorname)
#define assert_nonvirtual_leaf(classname, kindname, accessorname) \
static_assert(!std::is_polymorphic<classname>::value, \
"no virtual methods are allowed in " # classname );
CODEBLOBS_DO(empty1, empty3, assert_nonvirtual_leaf)
#undef assert_nonvirtual_leaf
Likewise in codeBlob.hpp we could generate `enum CodeBlobKind` to cover all the
non-abstract classes and likewise generate the accessor methods `is_nmethod()`,
`is_buffer_blob()` in class `CodeBlob` which allow the kind to be tested.
#define codekind_enum_tag(classname, kindname, accessorname) \
kindname,
enum CodeBlobKind : u1 {
None,
CODEBLOBS_DO(empty1, codekind_enum_tag, codekind_enum_tag)
Number_Of_Kinds
};
#define is_codeblob_define(classname, kindname, accessorname) \
void is_ # accessor_name () { return _kind == kindname; }
class CodeBlob {
. . .
CODEBLOBS_DO(empty1, is_codeblob_define, is_codeblob_define);
. . .
There may be other opportunities to use the iterator (e.g. in vmStructs.cpp?)
but this looks like a good start.
-------------
PR Review Comment: https://git.openjdk.org/jdk/pull/23533#discussion_r1948849392
