Dissassembly of Forth code words with 'see'

user_7544399 0
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I am preparing overall knowledge on building a Forth interpreter and want to disassemble some of the generic Forth code words such as +, -, *, etc.

My Gforth (I currently have version 0.7.3, installed on Ubuntu Linux) will allow me to disassemble colon definitions that I make with the command see, as well as the single code word .. But when I try it with other code words, see + or see /, I get an error that says, Code +, and then I'm not able to type in my terminal anymore, even when I press control-c.

I should be able to decompile/disassemble the code words, as shown by the Gforth manual: https://www.complang.tuwien.ac.at/forth/gforth/Docs-html/Decompilation-Tutorial.html

Has anyone else had this issue, and do you know how to fix it?

gforth forth
4 Answers

Most versions of SEE that I've seen are meant only for decompiling colon definitions. + and / and other arithmetic operations are usually written in assembly code and SEE doesn't know what to do with them. That's why you were getting the CODE error message: they're written in code, not Forth. There are several Forth implementations I've seen that have built in assemblers, but I don't think I've ever seen a dis-assembler. Your best bet for seeing the inner workings of + or / or other such words might be to use DUMP or another such word to get a list of the bytes in the word and either disassemble the word by hand or feed the data into an external disassembler. Or see if you can find the source code for your implementation or a similar one.

user_109770640

SEE is a word that has not a tightly controlled behaviour. It is a kind of best effort to show the code of a word X if invoked as

SEE X

It behaves slightly different according how difficult it is to do this. If you defined the word yourself in the session, you're pretty much guaranteed to get your code back. If it is a built in word, especially if it is a very elementary word like + , it is harder. It may look nothing much like the original definition, because of optimisation or compilation into machine code.

Specifically for gforth, if it gets hard gforth invokes the standard tools that are present on the system to analyse object files. So it may be necessary to install gdb and/or investigate how gforth tries to connect to it. For the concrete example of Ubuntu and gforth 0.7.3 Lutz Mueller gives a recipee.

.

user_13749750

I think SEE does it's job as designed. There are words in FORTH defined in machine code (often called as primitives) and also there is a possibility to define machine code via assembler by the user ie.: : MYCODE assembler memonics ;CODE

So the output of SEE shows not Code error, but that (ie.) + word was defined as machine code and one can see the disassembled mnenonics on the right of it's output.

user_155560200
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