On Mon, Jan 12, 2015 at 12:11 PM, Borislav Petkov <[email protected]> wrote: > On Mon, Jan 12, 2015 at 11:46:53AM -0800, Andy Lutomirski wrote: >> Dumb example: >> >> pushq_cfi $__KERNEL_DS /* ss */ >> >> This doesn't save anything that the unwinder would care about. > > And? The unwinder or whatever looks at that info simply ignores stuff it > is not interested in, no?
But CFI_REL_OFFSET $__KERNEL_DS, 0 probably isn't even well-formed and won't build. > >> Better example: >> >> pushq_cfi \child_rip /* rip */ >> CFI_REL_OFFSET rip,0 >> >> Doing this with a macro would need a fancier macro. > > I'd ask first whether we really need this at all. > >> Then there's crap like: >> >> pushq_cfi %rdi >> SCHEDULE_USER >> popq_cfi %rdi > > I guess we can add a gas regname argument optional and if it is set, use > it and if not, use the reg itself... Or something like that in the best > effort type of approach. > >> I would need to look a lot more carefully to figure out whether this >> would need CFI_REL_OFFSET. >> >> If we actually had a DWARF unwinder in the kernel, maybe we could have >> real test cases :-/ > > I don't think that's ever going to happen. > > I'd say we do the CFI annotation on a best effort basis but not > sacrifice readability in the process. If it can't be annotated, well, > tough luck. > This stuff is at least useful (in theory) for debugging with gdb. And I wouldn't mind an optional DWARF unwinder to get higher quality backtraces. Obviously any such thing would need to be quite robust. I think SuSE has one. > -- > Regards/Gruss, > Boris. > > Sent from a fat crate under my desk. Formatting is fine. > -- -- Andy Lutomirski AMA Capital Management, LLC -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
