Thread: Compiler in C?

Originally Posted by laserlight

That would not be necessary at all. Remember, we are talking about what can be done, not what is typically done.

hmmm. okay. So you are saying the process of compiling the compiler takes care of this apparent paradox?

This sounds kind of like baking rye or sourdough, where you need some small piece of already made dough as an ingredient. I guess, as matsp says, the "primal compiler" was in asm...

Originally Posted by MK27

So you are saying the process of compiling the compiler takes care of this apparent paradox?

Yes.

As a side note, you might want to read Ken Thompson's Reflections on Trusting Trust.

Originally Posted by laserlight

As a side note, you might want to read Ken Thompson's Reflections on Trusting Trust.

Neat. But:

We install this binary as the official C. We can now remove the bugs from the source of the compiler and the new binary will reinsert the bugs whenever it is compiled. Of course, the login command will remain bugged with no trace in source anywhere.

Would that mean if you rebuilt the compiler, using the corrected (unbugged) source, and the (only available) bugged, pre-built compiler, that the new compiler would recognize that it is being re-built and insert this "Trojan Horse" code?

I guess so...

Originally Posted by MK27

Would that mean if you rebuilt the compiler, using the corrected (unbugged) source, and the (only available) bugged, pre-built compiler, that the new compiler would recognize that it is being re-built and insert this "Trojan Horse" code?

Yes.

Originally Posted by MK27

But surely, sir, there is a ton of __inline asm__ in there?

Not at all. I would be very surprised if there is more than a few lines of inline assembler in gcc (if any). It makes the compiler less portable for one thing (and although a compiler compiling for a certain target obviously needs to know the machine code of the target system, but that's not to say that you don't want a x86 compiler to work from a Sparc system, for example - if the compiler for x86 has x86 assembler in it, then it would not compile on a Sparc system.

Most of what compilers do is a load of string handling, binary trees, hash-tables and such.

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Mats