On Sun, Aug 24, 2014 at 12:07 AM, Richard Stallman <r...@gnu.org> wrote:
> The research is all done. We just need to implement it.
>
> I would describe this as a domain for research, because it is
> far from clear whether it could possibly work in practice;
> if it could, it is not obvious how to make it work.
>
> It's not like writing an assembler, where we know it can work.
We don't actually know the assembler _does_ work. That's what I tried to
say. I didn't want to over-emphasise it, because I thought people might
already be bored of me banging on about it But apparently not! The problem
is the semantics of the whole GNU toolchain are inaccessible because they
depend 100% on the proprietary non-free tools that were used to build them.
This is important, so let me make a statement:
There is not one single line of GNU source code, the meaning
of which does not depend entirely on non-free proprietary
software.
The source code will not tell you what the software actually does. See
Thompson's 1984 Turing Award Speech
http://www.ece.cmu.edu/~ganger/712.fall02/papers/p761-thompson.pdf for the
details. I quote:
"The moral is obvious. You can't trust code that you did not
totally create yourself. (Especially code from companies
that employ people like me.) "
He works for Google now, doesn't he :-)
The trick Thompson demonstrates is what I call a _syntactic fixed-point_.
He basically makes a Y combinator of the C compiler, so that it takes in
its own source and outputs it again, but that does not mean that the source
it outputs is the source you read when you look at the source-distribution.
The solution is to establish a _semantic_ fixedpoint. But to do that we
need to be able to generate arbitrarily many essentially different working
implementations of the compiler, and make sure that the code it generates
when it compiles itself is the same, whatever the particular
implementation. So if we see that the version that we compiled into MS Word
BASIC produces the same binary executable as the JavaScript and COBOL
versions then we can have some more confidence that the semantics of the
GNU toolchain haven't been hijacked, ... yet.
Ian
