Re: [Unix-jun72] status on disassembler

Doug Merritt wrote: I'm confused. Those are both the same, aren't they? Isn't the simplest thing to do 2 passes and generate numeric labels as needed? i.e. L0001: br L0002 br L0001 L0002: That's ugly, but it's correct and will assemble so I'd start there. Once you have that, and you have all the code in memory as some sort of tree, it should be possible to make a pass an attempt to clean this up a little. Here's a snipped of real code, with the uninteresting parts turned into "..." badsys: ... mov $3f,u.namep ... br 1f ... br 2f 1: ... 2: br sysexit 3: <core\0\0> ------- badsys: ... mov $L0001,u.namep ... br L0002 ... br L0003 L0002: ... L0003: br sysexit L0001: <core\0\0> You should be able to scan the code and check for references to each location. Assume for a second you have an vector with one entry for each instruction location. You could then chain references off each element. With that information you could tell the "lifetime" of a label. i.e. at L0001 above you could look and decide that that no one else referenced it going forward. I would think that as you scanned that vector from beginning to end you could keep a count of active references, and use that to reset your local label number. Let's try it. badsys: 01 ... 02 mov $L0001,u.namep 03 ... 04 br L0002 05 ... 06 br L0003 L0002: 07 ... L0003: 08 br sysexit L0001: 09 <core\0\0> 10 01 02 uses L0001 +1 03 04 uses L0002 +2 05 06 uses L0003 +3 07 defines L0002 +2; look forward, no refs to L0002 so decrement 08 defines L0003 +1; look forward, no refs to L0003 so decrement 09 defines L0001 0; look forward, no refs to L0001 so decrement 10 I'm probably trivializing it, but I'm willing to put my money where my mouth is if you want me to take a look at your code. I think it has to be a 2 pass operation, however. I think this is true of any good disassembler; they are generally multiple pass. Deciding where the "data" is sometimes takes a little work, which can sometimes be a heuristic like "it looks like ascii and there is a reference to it", so having a tree of references generally helps. This is not unlike binary recompilation where you follow each possible code path to a terminal node. -brad