On 03.08.2018 22:33, Nick Desaulniers wrote: > On Fri, Aug 3, 2018 at 12:09 PM John David Anglin <dave.anglin@xxxxxxxx> wrote: >> >> On 2018-08-03 2:11 PM, Nick Desaulniers wrote: >>> But the kernel uses the generic_THIS_IP_ *everywhere*, not parisc's >>> custom current_text_addr(). So if this did actually break unwinding, >>> you should have noticed by now. >> The unwind problem was noticed. > > So parisc is currently broken (doesn't unwind) due to the pervasive > use of _THIS_IP_ (generic C) throughout the kernel? I tested it on the 32bit kernel. The answer is: No. Unwinding works (with and without your patch). > If no, that implies this patch (generic C) causes no unwinding problems. correct. > If yes, that implies that the diff I posted later in this thread > (inline assembly) is preferable, and that parisc has bigger problems > (and probably needs to do rewrite the unwinding code to handle these > extra labels everywhere). > >> Patches were recently applied to gcc and binutils to try and fix it. >> The gcc patch moved >> branch tables to rodata so that the label at the head of the table >> wasn't in text. >> >> https://gcc.gnu.org/ml/gcc-patches/2018-07/msg01804.html >> https://sourceware.org/ml/binutils/2018-07/msg00474.html >> >> When I saw your suggested change, I realized there was another source of >> text labels >> that need linker relocations. > > Thank you for the links. > > On Fri, Aug 3, 2018 at 10:57 AM John David Anglin <dave.anglin@xxxxxxxx> wrote: >> The label breaks the unwind data, not the unwind code. So, localizing >> the use of >> current_text_addr() to the parisc unwind code doesn't help. > > Have you confirmed that applying my patch breaks *the ability to > unwind correctly*? I tested your patch (on 32bit). Your patch does not break anything. > It looks like return_address() is used in > ftrace_return_address(), so I assume you can boot a kernel with my > patch applied, and CONFIG_FTRACE=y, then run: > > $ sudo trace-cmd record -p function date > $ trace-cmd report | grep date- | less > > and see if the stacks aren't unwound or look messed up. I faced issues with trace-cmd, but calling ftracing functions manually worked. So, your patch is basically OK and doesn't break anything. But I agree with Dave that Andrew, that THIS_IP is ugly. Helge -- To unsubscribe from this list: send the line "unsubscribe linux-parisc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
