On Sat, Jul 23, 2016 at 02:39:52PM +0900, Linus Torvalds wrote: > On Sat, Jul 23, 2016 at 2:35 PM, Josh Poimboeuf <jpoim...@redhat.com> wrote: > > > > While doing the scanning and printing, it does call the frame pointer > > unwinder in parallel, but like before, that's *only* used to determine > > whether a found address should be printed without a question mark. If > > the unwinder goes off the rails, the scanning and printing of text > > addresses goes on, undisturbed. > > > > The frame pointer unwinder code itself is quite careful not to > > dereference anything it shouldn't (though of course I welcome any review > > comments that find otherwise). > > So this was the bug the last time around we did unwinders - the code > would dereference the unwind tables, and the tables would be > corrupted. End result: recursive oops. > > And they were corrupted not even because of memory corruption, but > simply because they contained incorrect data, due to compiler bugs and > other issues. > > I have really bad memories from that time. Several years after the > fact. It took months to finally revert the crap, because the author > continued to insist that "this was the last bug" for several passes > through that thing. > > As they say, "Once burned, twice shy". But in this case, it's more > like "Four times burned, sixteen times as shy".
But that was DWARF, right? This is still just simple frame pointers. Don't think of it as a new unwinder. Think of it instead as a "gentle reshuffling of the existing code to vastly improve readability and maintenance." Yes, I would like to eventually propose a DWARF unwinder, which hopefully learns from the mistakes of previous attempts. But either way, I think this patch set stands on its own as a big improvement. -- Josh