On Fri, 24 May 2019 13:26:08 +0200 Peter Zijlstra <pet...@infradead.org> wrote:
> But but but but.. why not add all the required bits to the shadow stack > in the first place and do away with the array entirely? What required bits would that be? The pointer to the fgraph_ops, because we need that to pass to the calling function. > > So on ret, just keep POP'ing until either the stack is empty or the > entry is for another function. When we hit a fgraph_ops, how do we know if it was freed or not? We can't just blindly reference it. The idea of the array, is that we can maintain state in a single location of when the fgraph_ops is freed. If we return from a function, we have an index and a counter, and if the counter doesn't match with what's in the array, then we know that the fgraph_ops is no longer around and we just drop it. The reason for the array, is to keep track of if the fgraph_ops has been freed or not. Otherwise, when we unregister the fgraph_ops, we would need to search all shadow stacks, looking for it to unreference it. Believe me, I rather not have that array, but I couldn't come up with a better solution to handle freeing of fgraph_ops. -- Steve
