David Daney wrote: > Nigel Stephens wrote: > > > > > >David Daney wrote: > > > >>Atsushi Nemoto wrote: > >> > >>>On Thu, 27 Jul 2006 20:12:45 +0100, Thiemo Seufer <ths@xxxxxxxxxxxx> > >>>wrote: > >>> > >>>>IOW, binary analysis can't be expected to provide full accuracy, but > >>>>we can live with a reasonable approximation, I think. > >>> > >>> > >>> > >>>Yes, this is a starting point. > >>> > >>>The patch (and current mips get_wchan() implementation) tries to do is > >>>what I used to do to analyze stack dump by hand. > >>> > >>>1. Determine PC and SP. > >>>2. Disassemble a function containing the PC address. > >>>3. If the function is leaf, make use RA for new PC. > >> > >> > >>This was always the tricky part for me. How do you know if the > >>function is a leaf? > >> > > > >I think that if you cannot find a store instruction which saves RA to > >the stack -- either because it's a real leaf and there is no such store, > >or because the PC hasn't yet reached the store instruction -- then in > >both cases it can be treated as a leaf. > > Presumably you are walking the code back from the PC until you find the > prolog. How would you tell if you had gone past the beginning of a leaf > function? If you find a j $31 you might assume that it was the end of > the previous function. > > But that does not work if you are in a function that has multiple return > points. On encountering a j $31 you have no way of telling if you are > in a leaf function or a non-leaf function with multiple return points. ... or in a fragment of a single return function which was moved out of the hot path, after the return point. Thiemo
