part1

VM_STRUCTS(GENERATE_NONSTATIC_VM_STRUCT_ENTRY, GENERATE_STATIC_VM_STRUCT_ENTRY, GENERATE_UNCHECKED_NONSTATIC_VM_STRUCT_ENTRY, GENERATE_NONSTATIC_VM_STRUCT_ENTRY, GENERATE_NONPRODUCT_NONSTATIC_VM_STRUCT_ENTRY, GENERATE_C1_NONSTATIC_VM_STRUCT_ENTRY, GENERATE_C2_NONSTATIC_VM_STRUCT_ENTRY, GENERATE_C1_UNCHECKED_STATIC_VM_STRUCT_ENTRY, GENERATE_C2_UNCHECKED_STATIC_VM_STRUCT_ENTRY)

part2

//-------------------------------------------------------------------------------- // VM_STRUCTS // // This list enumerates all of the fields the serviceability agent // needs to know about. Be sure to see also the type table below this one. // NOTE that there are platform-specific additions to this table in // vmStructs__.hpp. #define VM_STRUCTS(nonstatic_field, \ static_field, \ unchecked_nonstatic_field, \ volatile_nonstatic_field, \ nonproduct_nonstatic_field, \ c1_nonstatic_field, \ c2_nonstatic_field, \ unchecked_c1_static_field, \ unchecked_c2_static_field) \

is usually

#define type alias

But here we see

#define type ___

I underline it to mean nothing.

If you really just "bring people" to replace it, then there will be nothing above it. Even if you substitute all the parameters,
but#define type ___is Nothing.

How do you understand the above syntax?

Source code comes from jdk8.