On Fri, Mar 1, 2019 at 5:29 PM Josh Poimboeuf <jpoimboe@xxxxxxxxxx> wrote: > > On Fri, Mar 01, 2019 at 10:24:18AM -0600, Josh Poimboeuf wrote: > > > Is there a reason why the top-level Makefile only sets > > > -fno-optimize-sibling-calls if CONFIG_FRAME_POINTER is set? > > > I suspect that this is just a historical thing, because reliable > > > unwinding didn't work without frame pointers until ORC came along. > > > I'm not quite sure how best to express "don't do tail optimization if > > > either frame pointers are used or ORC is used" in a Makefile, and > > > whether we want an indirection through Kconfig for that, so I'm not > > > doing anything about it in this series. > > > Can someone send a patch to deal with it properly? > > > > Why would sibling calls be a problem for ORC? Once a function does a > > sibling call, it has effectively returned and shouldn't show up on the > > stack trace anyway. > > Answering my own question, I guess some people might find it confusing > to have a caller skipped in the stack trace. But nobody has ever > complained about it. > > It's not a problem for livepatch since we only care about the return > path. Yeah, that's my concern. I understand that it's irrelevant for tooling that wants to understand what context a function is running in, but it might matter to a human trying to understand how a function was reached. In a theoretical worst case, a stack trace might skip directly from do_syscall_64() into some random helper function that received a bad pointer, and that might make debugging harder.
