Re: CUP/LEX has limitations

Scott Nicol <snicol@apk.net> wrote:
> I haven't used CUP/LEX, but I'm quite familiar with the "code too
> large" error in Java. Java has a limit of 64k code per method (you,
> like I, might be wondering what was being smoked when that decision
> was made).


This 64k code per method limit seems really accidental. In Java class
files, the actualy bytecode is stored in an attribute named 'Code'. This
attribute has a specified structure, as defined in JVM spec § 4.7.3,
which is as follows:


Code_attribute {
         u2 attribute_name_index;
         u4 attribute_length;
         u2 max_stack;
         u2 max_locals;
         u4 code_length;
         u1 code[code_length];
         u2 exception_table_length;
         { u2 start_pc;
         u2 end_pc;
         u2 handler_pc;
         u2 catch_type;
         } exception_table[exception_table_length];
         u2 attributes_count;
         attribute_info attributes[attributes_count];
}


So, in the attribute structure, there is four bytes allocated for the
length of the actual content (code_length). However, there is another
constraint at JVM spec § 4.8.1, which states that "The value of the
code_length item must be less than 65536."


If the specification was internally coherent, the type of code_length
would be u2, wouldn't it? With this structure, there's a huge
unnecessary overhead of two bytes per method in the class file. ;)


br,
Pietu Pohjalainen

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