Your assembly is my domain-specific language


A few years ago I set out to write a clone of Sinclair BASIC as a domain-specific language (DSL) in Groovy. The end result was BINSIC, but it was much closer to an interpreter than a DSL: it turned out that strange ways that Groovy handled capitalised function/closure names meant that I could not match keywords at all and so interpretation became the only option (though there were DSL-like features lurking under the covers).

Now I have set out to write an interpreter for RISCV assembly and have written something which is much more like a DSL. My aim was to track the memory reference patterns of various real-time benchmarks running on RISCV systems – based on the disassembly generated by Spike, the RISCV emulator.

Getting that done requires tracking register state – because in true RISC fashion reads and writes are done not to immediates, but to addresses held in registers with immediates used as offsets.

To make this happen every (or at least every used) RISCV instruction is mapped to a closure and the operands treated as closure parameters. The closures are all inside the RegisterFile class so all can access the registers to keep the state updated. This makes it quite like a DSL but I make no claims for purity: every statement is passed through a regular expression based interpreter to separate out the parameters: if nothing else that eliminates a lot of boilerplate code that would have to be stuck inside the closures.

Memory is treated as a sparse array through a Groovy Map instance – with an address (64-bit Long) mapped to an 8-bit Byte.

The process isn’t perfect – a disassembly doesn’t given you the contents of initialised data, so an attempt to access those addresses is quite likely to raise an exception which needs to be trapped and the memory accounted for – by simply assigning zero to the address: it’s a kludge but it seems to work.

Computer scientists’ lousy citation style


I am reading this book: Soft Real-Time Systems: Predictability vs. Efficiency, and I am struck, once again, by the truly lousy style of publication reference that seem to be preferred by so many

Journal of the American Mathematical Society
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computer scientists,

The style used in the book appears to be that favoured by the American Mathematical Society – the so-called “authorship trigraph” – with references made up of letters from the author’s name followed by the last two figures of the year of original publication eg., [Bak91] which references in the bibliography:

[Bak91]        T.P. Baker. Stack-based scheduling of real-time processes. Journal of Real Time Systems, 3, 1991.

Now it is possible, if I were an expert in the field that I might recognise this reference, but it is far from helpful. When referencing papers written by multiple authors the system is hopeless – using the first letters of the first three authors and ignoring the rest, eg., [DGK^+02] is a real reference in the book to a paper with eight authors. I really doubt many people would get that straight away.

But at least this reference system contains slightly more than the IEEE‘s citation system, which demands papers are merely referenced by a bracketed number in the text, eg., [1].

These reference systems are so widely used that I worried that my own use of the Chicago system – which specifies author and year, eg., (Denning, 1970), would be frowned upon in Birkbeck – but a re read of the regulations showed their demand was for a consistent and well-recognised system.

The ACM, too, promote a sensible citation format eg., [Denning 1970].

Does this matter? Yes. I am sure many readers of these books and papers are students who are conducting literature reviews or similar exercises. Reading the original reference may often be important and having to flick back and forth to a bibliography to check the meaning of an incomprehensible reference is not calaculated to add to the sum of human happiness.

(I don’t have any real complaints about the book though – except that the translation is plainly a bit stilted – for instance, the first sentence of the book refers to real time systems being investigated “in the last years” – a fairly common mistake in syntax from non-English speakers and one that the editors really ought to have corrected. But the occasional infelicity of language does not detract from the book’s overall appeal.)