Re: [PATCH v4 11/16] objtool: Add --mnop as an option to --mcount

Naveen N. Rao
2022-10-10T11:38:22Z

Sathvika Vasireddy wrote:
> Some architectures (powerpc) may not support ftrace locations being nop'ed
> 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 --mnop
> as an option to objtool --mcount, to indicate support for the same.
>
> Also, make sure that --mnop can be passed as an option to objtool only when
> --mcount is passed.
>
> 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(-)
>
> 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 += -DCC_USING_NOP_MCOUNT
> + ifdef CONFIG_HAVE_OBJTOOL_NOP_MCOUNT
> + CC_FLAGS_USING += -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_USER
> 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
>
> +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 = \
> $(if $(CONFIG_HAVE_NOINSTR_HACK), --hacks=noinstr) \
> $(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
disabled. I think we should make this depend on
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 = \
$(if $(CONFIG_HAVE_JUMP_LABEL_HACK), --hacks=jump_label) \
$(if $(CONFIG_HAVE_NOINSTR_HACK), --hacks=noinstr) \
$(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, --mcount)) \
$(if $(CONFIG_UNWINDER_ORC), --orc) \
$(if $(CONFIG_RETPOLINE), --retpoline) \
$(if $(CONFIG_RETHUNK), --rethunk) \

- Naveen