From: Steven Rostedt <rostedt@goodmis.org>
To: Oscar Carter <oscar.carter@gmx.com>
Cc: Ingo Molnar <mingo@redhat.com>, Kees Cook <keescook@chromium.org>,
linux-kernel@vger.kernel.org,
kernel-hardening@lists.openwall.com, Jann Horn <jannh@google.com>
Subject: Re: [PATCH v2 2/2] kernel/trace: Remove function callback casts
Date: Fri, 24 Jul 2020 14:34:57 -0400 [thread overview]
Message-ID: <20200724143457.27755412@oasis.local.home> (raw)
In-Reply-To: <20200724175500.GD3123@ubuntu>
On Fri, 24 Jul 2020 19:55:00 +0200
Oscar Carter <oscar.carter@gmx.com> 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.
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 ;-)
-- Steve
next prev parent reply other threads:[~2020-07-24 18:35 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-19 15:50 [PATCH v2 0/2] kernel/trace: Remove function callback casts Oscar Carter
2020-07-19 15:50 ` [PATCH v2 1/2] kernel/trace: Prepare to remove " Oscar Carter
2020-07-19 15:50 ` [PATCH v2 2/2] kernel/trace: Remove " Oscar Carter
2020-07-21 18:05 ` Steven Rostedt
2020-07-24 16:19 ` Oscar Carter
2020-07-24 16:35 ` Steven Rostedt
2020-07-24 17:14 ` Oscar Carter
2020-07-24 17:24 ` Oscar Carter
2020-07-24 17:36 ` Steven Rostedt
2020-07-24 17:40 ` Steven Rostedt
2020-07-24 17:48 ` Steven Rostedt
2020-07-24 17:55 ` Oscar Carter
2020-07-24 18:34 ` Steven Rostedt [this message]
2020-07-25 15:09 ` Oscar Carter
2020-07-25 15:19 ` Oscar Carter
2020-07-26 15:52 ` Oscar Carter
2020-07-27 13:53 ` Steven Rostedt
2020-07-31 14:41 ` Oscar Carter
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