Re: [PATCH v2 2/2] kernel/trace: Remove function callback casts
From: Steven Rostedt
Date: Fri Jul 24 2020 - 14:36:35 EST
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:
#define ARCH_SUPPORTS_FTRACE_OPS 1
select HAVE_DYNAMIC_FTRACE_WITH_REGS if 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.
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.
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 ;-)