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SubjectRe: [PATCH v7 04/10] ppc64 ftrace_with_regs configuration variables
On Fri, 5 Feb 2016 15:05:17 +0100
Petr Mladek <pmladek@suse.com> wrote:

> On Mon 2016-01-25 16:29:54, Torsten Duwe wrote:
> > diff --git a/arch/powerpc/kernel/ftrace.c b/arch/powerpc/kernel/ftrace.c
> > index ef8b916..29b7014 100644
> > --- a/arch/powerpc/kernel/ftrace.c
> > +++ b/arch/powerpc/kernel/ftrace.c
> > @@ -28,6 +28,11 @@
> >
> >
> > #ifdef CONFIG_DYNAMIC_FTRACE
> > +#if defined(CONFIG_DYNAMIC_FTRACE_WITH_REGS) && defined(CONFIG_PPC64) && \
> > + !defined(CC_USING_MPROFILE_KERNEL)
> > +#error "DYNAMIC_FTRACE_WITH_REGS requires working -mprofile-kernel"
> > +#endif
>
> CONFIG_DYNAMIC_FTRACE_WITH_REGS is automatically enabled when
> both CONFIG_DYNAMIC_FTRACE and HAVE_DYNAMIC_FTRACE_WITH_REGS
> are enabled.
>
> Therefore it is not possible to build kernel with broken gcc
> and DYNAMIC_FTRACE.
>
> IMHO, we need to allow to explicitely disable DYNAMIC_FTRACE_WITH_REGS
> if the compiler is broken to get around this build error.
>
> We either need to define DYNAMIC_FTRACE_WITH_REGS as a proper
> bool with description, help text, ... Or we need a way to
> explicitely disable HAVE_DYNAMIC_FTRACE_WITH_REGS. Or something
> like this.
>

You mean something like this?

(not tested)

-- Steve

diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index e45db6b0d878..19377bacebfc 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -470,6 +470,19 @@ config DYNAMIC_FTRACE_WITH_REGS
def_bool y
depends on DYNAMIC_FTRACE
depends on HAVE_DYNAMIC_FTRACE_WITH_REGS
+ depends on !DISABLE_DYNAMIC_FTRACE_WITH_REGS
+
+config DISABLE_DYNAMIC_FTRACE_WITH_REGS
+ bool "Force build to not have function tracer pass in registers"
+ depends on DYNAMIC_FTRACE
+ depends on HAVE_DYNAMIC_FTRACE_WITH_REGS
+ help
+ If the architecture supports passing in registers to the function
+ tracer, then that is automatically enabled. But there may be some
+ compilers out there that are broken and cause this to fail.
+ This option makes the build think that the architecture does not
+ support the register passing and allows the build to work even
+ with compilers that do not support the feature.g

config FUNCTION_PROFILER
bool "Kernel function profiler"
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