Status update and lookahead

16 Oct 2020

Since the last status update (that is, within the last month) the following language features have been implemented:

* All operations and relations on basic types (save reals)

* The relation IN for integers and sets

* Global RECORD variables

* Global ARRAY variables - thei required adjustment of the addressing mode within the backend

* Compilation of a global proper PROCEDURE body

* Local procedure variable addressing

* Value parameters of basic types (save reals)

* Variable parameters of basic types (save reals)

* Value and variable parameters of structured types, including open and fixed arrays

* Standard procedure LEN applied to global and local arrays

* Procedure call statement

* All of the above covered with tests

I am now looking at implementing strings, [ccall] calling convention and some sort of static linking (into a host OS executable). These three features will make it possible to compile a “Hello world” program.

When that milestone is achieved, I will need to implement IF and WHILE statements, and from then on it would be possible to develop a proto-kernel for BlackBox/64 alongside with Herschel. In greater detail:

As the development of Herschel continues, it will become necessary to implement features dealing with dynamic memory. Testing these features requires a run-time environment. Normally, this environment is provided by the BB Kernel. But it is not available for 64bits! Instead of developing a special testing env for the purposes of Herschel testing and development, I am looking at starting with a proto-kernel and gradually developing it into a full-featured 64-bit BB kernel.

The first and most essential features to put in the proto-kernel are, well, trap handling and trap reporting. You do expect Herschel-compiled programs to crash while Herschel is under development, and post-mortem analysis is critical to removing errors in Herschel. So, there is a need for [ccall] support in order to make host OS calls to output to the console and to set up trap handling and signal callbacks. (to handle segmentation violation).

Once console output and trap/signal handling is implemented, the memory allocator (procedure NEW implementation) can be put into the proto-kernel. It will require libc’s malloc calls and maybe some others; most other processing is done within the kernel with a limited number of CP features. (Note that the garbage collector doesn’t need to be ported from 32bit kernel until the whole Herschel is finished.)

Thus, with a proto-kernel as described it will be possible to continue the testing and development of Herschel without the extra work of creating a special testing environment. Eventually, the proto-kernel will become the new BB 64-bit kernel by adding to it all the features that the kernel provides.