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SubjectRe: [PATCH 3/5] kernel hacking: new config NO_AUTO_INLINE to disable compiler atuo-inline optimizations
On Tue, May 01, 2018 at 10:54:20AM -0400, Steven Rostedt wrote:
> On Tue, 1 May 2018 21:00:12 +0800
> changbin.du@intel.com wrote:
>
> > From: Changbin Du <changbin.du@intel.com>
> >
> > This patch add a new kernel hacking option NO_AUTO_INLINE. Selecting
> > this option will make compiler not auto-inline kernel functions. By
> > enabling this option, all the kernel functions (including static ones)
> > will not be optimized out except those marked as inline or always_inline.
> > This is useful when you are using ftrace to understand the control flow
> > of kernel code or tracing some static functions.
>
> I'm not against this patch, but it's up to others if this gets included
> or not.
>
> >
> > Signed-off-by: Changbin Du <changbin.du@intel.com>
> > Cc: Steven Rostedt <rostedt@goodmis.org>
> > ---
> > Makefile | 6 ++++++
> > lib/Kconfig.debug | 13 +++++++++++++
> > 2 files changed, 19 insertions(+)
> >
> > diff --git a/Makefile b/Makefile
> > index 619a85a..eb694f6 100644
> > --- a/Makefile
> > +++ b/Makefile
> > @@ -775,6 +775,12 @@ KBUILD_CFLAGS += $(call cc-option, -femit-struct-debug-baseonly) \
> > $(call cc-option,-fno-var-tracking)
> > endif
> >
> > +ifdef CONFIG_NO_AUTO_INLINE
> > +KBUILD_CFLAGS += $(call cc-option, -fno-inline-functions) \
> > + $(call cc-option, -fno-inline-small-functions) \
> > + $(call cc-option, -fno-inline-functions-called-once)
> > +endif
> > +
> > ifdef CONFIG_FUNCTION_TRACER
> > ifndef CC_FLAGS_FTRACE
> > CC_FLAGS_FTRACE := -pg
> > diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> > index c40c7b7..90f35ad 100644
> > --- a/lib/Kconfig.debug
> > +++ b/lib/Kconfig.debug
> > @@ -198,6 +198,19 @@ config GDB_SCRIPTS
> > instance. See Documentation/dev-tools/gdb-kernel-debugging.rst
> > for further details.
> >
> > +config NO_AUTO_INLINE
> > + bool "Disable compiler atuo-inline optimizations"
>
> typo: s/atuo/auto/
>
> > + default n
> > + help
> > + This will make compiler not auto-inline kernel functions for
> > + optimization. By enabling this option, all the kernel functions
> > + (including static ones) will not be optimized out except those
> > + marked as inline or always_inline. This is useful when you are
> > + using ftrace to understand the control flow of kernel code or
> > + tracing some static functions.
>
> Some grammar updates:
>
> This will prevent the compiler from optimizing the kernel by
> auto-inlining functions not marked with the inline keyword.
> With this option, only functions explicitly marked with
> "inline" will be inlined. This will allow the function tracer
> to trace more functions because it only traces functions that
> the compiler has not inlined.
>
> Enabling this function can help debugging a kernel if using
> the function tracer. But it can also change how the kernel
> works, because inlining functions may change the timing,
> which could make it difficult while debugging race conditions.
>

Thanks for your kind grammar updates. I will update them. :)

> > +
> > + Use only if you want to debug the kernel.
>
> The proper way to say the above is:
>
> If unsure, select N
>
Agree.

> -- Steve
>
> > +
> > config ENABLE_WARN_DEPRECATED
> > bool "Enable __deprecated logic"
> > default y
>


--
Thanks,
Changbin Du

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