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? If no, that implies this patch (generic C) causes no unwinding problems. 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*? 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. -- Thanks, ~Nick Desaulniers -- 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
