"Rodney M. Bates" <[EMAIL PROTECTED]> writes: > The following example C code and disassembly is compiled by gcc 3.4.3, > for i686. It uses two different invariants for what the value of > a static link is. Everywhere inside P, static link values are consistently > the same as base pointer (%ebp) register values for the same activation > record. A static link value is generated at 4c: in P, and used at > 22: in PInner2 and c: in PInner1. > > Everywhere inside similar function Q, static link values consistently point > 8 bytes higher than where the base register points. A value is generated at > d9: in Q and used at 7a: in Qinner2 and 64: in QInner1. > > From the examples I have looked at, it looks like it is correct translation, > and, expect for seeming strangeness, is not a problem for execution. > > However, I am working on an extended gdb-derived debugger that works, > in part, with code produced by a gcc-derived code generator for > Modula-3. So far, I can't find out, in the debugger, which invariant > is in use. I have the debugger correctly both generating and using > static links when evaluating user-typed expressions, using the first > invariant. I could easily change it to use the second invariant, but > obviously, that would fix some cases and break others. > > Is there a compelling reason for this difference? If not, I would like to > make it all use invariant one. Also, does anybody know where in gcc this > difference is happening? I poked around in the source for a couple of hours, > but didn't see anything obvious.
The static link pointer points to a part of the stack frame which includes the information required for the nested functions. The amount of information required changes depending on the code. Therefore, the static link pointer will not be a constant offset from the frame pointer. I don't believe that it is possible to change this while still handling calls between doubly nested functions, but maybe I just haven't thought about it hard enough. > BTW, this is using stabs. I know that is not very complete, but it would be > a lot more work than I want to do to change it. Stabs doesn't represent the static link pointer at all, so that is your problem. You should switch to DWARF. If that is impossible as you suggest, then I think your most profitable approach would be to enhance stabs somehow. Ian
