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Date:   Mon, 10 Oct 2022 17:07:46 +0530
From:   "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>
Subject: Re: [PATCH v4 11/16] objtool: Add --mnop as an option to --mcount
To:     linuxppc-dev@lists.ozlabs.org,
        Sathvika Vasireddy <sv@linux.ibm.com>
Cc:     aik@ozlabs.ru, chenzhongjin@huawei.com,
        christophe.leroy@csgroup.eu, jpoimboe@redhat.com,
        linux-kernel@vger.kernel.org, mbenes@suse.cz, mingo@redhat.com,
        mpe@ellerman.id.au, npiggin@gmail.com, peterz@infradead.org,
        rostedt@goodmis.org
References: <20221002104240.1316480-1-sv@linux.ibm.com>
        <20221002104240.1316480-12-sv@linux.ibm.com>
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Sathvika Vasireddy wrote:
> Some architectures (powerpc) may not support ftrace locations being nop'e=
d
> out at build time. Introduce CONFIG_HAVE_OBJTOOL_NOP_MCOUNT for objtool, =
as
> a means for architectures to enable nop'ing of ftrace locations. Add --mn=
op
> as an option to objtool --mcount, to indicate support for the same.
>=20
> Also, make sure that --mnop can be passed as an option to objtool only wh=
en
> --mcount is passed.
>=20
> Signed-off-by: Sathvika Vasireddy <sv@linux.ibm.com>
> ---
>  Makefile                                |  4 +++-
>  arch/x86/Kconfig                        |  1 +
>  kernel/trace/Kconfig                    |  7 +++++++
>  scripts/Makefile.lib                    |  1 +
>  tools/objtool/builtin-check.c           | 14 ++++++++++++++
>  tools/objtool/check.c                   | 19 ++++++++++---------
>  tools/objtool/include/objtool/builtin.h |  1 +
>  7 files changed, 37 insertions(+), 10 deletions(-)
>=20
> diff --git a/Makefile b/Makefile
> index a5e9d9388649..b2230ad14748 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -857,7 +857,9 @@ ifdef CONFIG_FTRACE_MCOUNT_USE_CC
>    endif
>  endif
>  ifdef CONFIG_FTRACE_MCOUNT_USE_OBJTOOL
> -  CC_FLAGS_USING	+=3D -DCC_USING_NOP_MCOUNT
> +  ifdef CONFIG_HAVE_OBJTOOL_NOP_MCOUNT
> +    CC_FLAGS_USING	+=3D -DCC_USING_NOP_MCOUNT
> +  endif
>  endif
>  ifdef CONFIG_FTRACE_MCOUNT_USE_RECORDMCOUNT
>    ifdef CONFIG_HAVE_C_RECORDMCOUNT
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index f9920f1341c8..2a79a05c4402 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -189,6 +189,7 @@ config X86
>  	select HAVE_CONTEXT_TRACKING_USER_OFFSTACK	if HAVE_CONTEXT_TRACKING_USE=
R
>  	select HAVE_C_RECORDMCOUNT
>  	select HAVE_OBJTOOL_MCOUNT		if HAVE_OBJTOOL
> +	select HAVE_OBJTOOL_NOP_MCOUNT		if HAVE_OBJTOOL_MCOUNT
>  	select HAVE_BUILDTIME_MCOUNT_SORT
>  	select HAVE_DEBUG_KMEMLEAK
>  	select HAVE_DMA_CONTIGUOUS
> diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
> index 1052126bdca2..9c696cb24756 100644
> --- a/kernel/trace/Kconfig
> +++ b/kernel/trace/Kconfig
> @@ -76,6 +76,13 @@ config HAVE_OBJTOOL_MCOUNT
>  	help
>  	  Arch supports objtool --mcount
>=20
> +config HAVE_OBJTOOL_NOP_MCOUNT
> +	bool
> +	help
> +	  Arch supports the objtool options --mcount with --mnop.
> +	  An architecture can select this if it wants to enable nop'ing
> +	  of ftrace locations.
> +
>  config HAVE_C_RECORDMCOUNT
>  	bool
>  	help
> diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
> index 3fb6a99e78c4..ce14e3b8577f 100644
> --- a/scripts/Makefile.lib
> +++ b/scripts/Makefile.lib
> @@ -234,6 +234,7 @@ objtool_args =3D								\
>  	$(if $(CONFIG_HAVE_NOINSTR_HACK), --hacks=3Dnoinstr)		\
>  	$(if $(CONFIG_X86_KERNEL_IBT), --ibt)				\
>  	$(if $(CONFIG_FTRACE_MCOUNT_USE_OBJTOOL), --mcount)		\
> +	$(if $(CONFIG_HAVE_OBJTOOL_NOP_MCOUNT), --mnop)                 \

This still won't help: for instance, if CONFIG_FTRACE itself is=20
disabled. I think we should make this depend on=20
CONFIG_FTRACE_MCOUNT_USE_OBJTOOL. The below change works for me:

diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index 54d2d6451bdacc..fd3f55a1fdb7bb 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -245,8 +245,8 @@ objtool_args =3D                                       =
                       \
        $(if $(CONFIG_HAVE_JUMP_LABEL_HACK), --hacks=3Djump_label)        \
        $(if $(CONFIG_HAVE_NOINSTR_HACK), --hacks=3Dnoinstr)              \
        $(if $(CONFIG_X86_KERNEL_IBT), --ibt)                           \
-       $(if $(CONFIG_FTRACE_MCOUNT_USE_OBJTOOL), --mcount)             \
-       $(if $(CONFIG_HAVE_OBJTOOL_NOP_MCOUNT), --mnop)                 \
+        $(if $(CONFIG_FTRACE_MCOUNT_USE_OBJTOOL),                       \
+             $(if $(CONFIG_HAVE_OBJTOOL_NOP_MCOUNT), --mcount --mnop, --mc=
ount)) \
        $(if $(CONFIG_UNWINDER_ORC), --orc)                             \
        $(if $(CONFIG_RETPOLINE), --retpoline)                          \
        $(if $(CONFIG_RETHUNK), --rethunk)                              \


- Naveen