Hi Steven, On Fri, Jul 24, 2020 at 02:34:57PM -0400, Steven Rostedt wrote: > On Fri, 24 Jul 2020 19:55:00 +0200 > Oscar Carter <oscar.carter@xxxxxxx> wrote: > > > > Which one of the above is this patch set for? > > > > This patch is the result of a warning obtained with the following: > > > > make allmodconfig ARCH=powerpc > > make ARCH=powerpc CROSS_COMPILE=powerpc-linux-gnu- -j4 > > > > And with the -Wcast-function-type enabled in the top level makefile. > > Looking into powerpc I found this: > > arch/powerpc/include/asm/ftrace.h: > > #ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS > #define ARCH_SUPPORTS_FTRACE_OPS 1 > #endif > > > arch/powerpc/Kconfig: > > select HAVE_DYNAMIC_FTRACE_WITH_REGS if MPROFILE_KERNEL > [..] > > config MPROFILE_KERNEL > depends on PPC64 && CPU_LITTLE_ENDIAN && FUNCTION_TRACER > def_bool $(success,$(srctree)/arch/powerpc/tools/gcc-check-mprofile-kernel.sh $(CC) -I$(srctree)/include -D__KERNEL__) > > So, it looks like you need to be 64bit PowerPC, Little Endian, and gcc > needs to support -mprofile. > > Otherwise, it falls back to the old way that does the type casting. > > If you are really concerned about this, I would recommend adding > support to the architecture you care about, and then this will no > longer be an issue. > > The funny part is, you can still add support for ftrace_ops, without > adding support for DYNAMIC_FTRACE_WITH_REGS, if you only care about not > having to do that typecast. I agree with you. I will try to add the support for ftrace_ops without adding support for DYNAMIC_FTRACE_WITH_REGS to the powerpc architecture. It's a great solution to allow a clean CFI build and so, protect this arch (powerpc) against attacks that try to modify the normal control flow. I take a look at the kernel documentation about port ftrace to other architectures [1] but it is out of date. If I try to do this I will need some help. Some info that point me to the right direction would be greatly appreciated. Some advice about what functions I will need to implement would be really helpfull. Or point me to the right piece of code that I can pick as base point. > My NAK still stands. I wont let an intrusive patch be added to the > ftrace core code to deal with an unsupported feature in an architecture. Don't worry. I agree with you and thanks for finding a better way to accomplish the initial purpose. > I would be will to add that linker trick to remove the warning. Or we > just use that warning as incentive to get architecture developers to > implement this feature ;-) In my opinion it would be better to leave the code as it an make the warning visible until this feature has been added. > -- Steve [1] https://www.kernel.org/doc/html/latest/trace/ftrace-design.html Thanks again, Oscar Carter
