Re: [RFC PATCH 1/4] objtool: Add --mnop as an option to --mcount

[Christophe Leroy]

Le 23/05/2022 à 19:55, Sathvika Vasireddy a écrit :
> Architectures can select HAVE_NOP_MCOUNT if they choose
> to nop out mcount call sites. If that config option is
> selected, then --mnop is passed as an option to objtool,
> along with --mcount.
> 

Is there a reason not to nop out mcount call sites on powerpc as well ?

> Also, make sure that --mnop can be passed as an option
> to objtool only when --mcount is passed.
> 
> Signed-off-by: Sathvika Vasireddy <sv@xxxxxxxxxxxxx>
> ---
>   Makefile                                |  4 +++-
>   arch/x86/Kconfig                        |  1 +
>   scripts/Makefile.build                  |  1 +
>   tools/objtool/builtin-check.c           | 14 ++++++++++++++
>   tools/objtool/check.c                   | 19 ++++++++++---------
>   tools/objtool/include/objtool/builtin.h |  1 +
>   6 files changed, 30 insertions(+), 10 deletions(-)
> 
> diff --git a/Makefile b/Makefile
> index 250707647359..acaf88e3c694 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -851,7 +851,9 @@ ifdef CONFIG_FTRACE_MCOUNT_USE_CC
>     endif
>   endif
>   ifdef CONFIG_FTRACE_MCOUNT_USE_OBJTOOL
> -  CC_FLAGS_USING	+= -DCC_USING_NOP_MCOUNT
> +  ifdef CONFIG_HAVE_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 1847d6e974a1..4a41bfb644f0 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -189,6 +189,7 @@ config X86
>   	select HAVE_CONTEXT_TRACKING_OFFSTACK	if HAVE_CONTEXT_TRACKING
>   	select HAVE_C_RECORDMCOUNT
>   	select HAVE_OBJTOOL_MCOUNT		if HAVE_OBJTOOL
> +	select HAVE_NOP_MCOUNT			if HAVE_OBJTOOL_MCOUNT
>   	select HAVE_BUILDTIME_MCOUNT_SORT
>   	select HAVE_DEBUG_KMEMLEAK
>   	select HAVE_DMA_CONTIGUOUS
> diff --git a/scripts/Makefile.build b/scripts/Makefile.build
> index ac8167227bc0..2e0c3f9c1459 100644
> --- a/scripts/Makefile.build
> +++ b/scripts/Makefile.build
> @@ -231,6 +231,7 @@ 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_NOP_MCOUNT), --mnop)				\
>   	$(if $(CONFIG_UNWINDER_ORC), --orc)				\
>   	$(if $(CONFIG_RETPOLINE), --retpoline)				\
>   	$(if $(CONFIG_SLS), --sls)					\
> diff --git a/tools/objtool/builtin-check.c b/tools/objtool/builtin-check.c
> index f4c3a5091737..b05e2108c0c3 100644
> --- a/tools/objtool/builtin-check.c
> +++ b/tools/objtool/builtin-check.c
> @@ -80,6 +80,7 @@ const struct option check_options[] = {
>   	OPT_BOOLEAN(0, "dry-run", &opts.dryrun, "don't write modifications"),
>   	OPT_BOOLEAN(0, "link", &opts.link, "object is a linked object"),
>   	OPT_BOOLEAN(0, "module", &opts.module, "object is part of a kernel module"),
> +	OPT_BOOLEAN(0, "mnop", &opts.mnop, "nop out mcount call sites"),
>   	OPT_BOOLEAN(0, "no-unreachable", &opts.no_unreachable, "skip 'unreachable instruction' warnings"),
>   	OPT_BOOLEAN(0, "sec-address", &opts.sec_address, "print section addresses in warnings"),
>   	OPT_BOOLEAN(0, "stats", &opts.stats, "print statistics"),
> @@ -142,6 +143,16 @@ static bool opts_valid(void)
>   	return false;
>   }
>   
> +static bool mnop_opts_valid(void)
> +{
> +	if (opts.mnop && !opts.mcount) {
> +		ERROR("--mnop requires --mcount");
> +		return false;
> +	}
> +
> +	return true;
> +}
> +
>   static bool link_opts_valid(struct objtool_file *file)
>   {
>   	if (opts.link)
> @@ -185,6 +196,9 @@ int objtool_run(int argc, const char **argv)
>   	if (!file)
>   		return 1;
>   
> +	if (!mnop_opts_valid())
> +		return 1;
> +
>   	if (!link_opts_valid(file))
>   		return 1;
>   
> diff --git a/tools/objtool/check.c b/tools/objtool/check.c
> index 190b2f6e360a..056302d58e23 100644
> --- a/tools/objtool/check.c
> +++ b/tools/objtool/check.c
> @@ -1175,17 +1175,18 @@ static void annotate_call_site(struct objtool_file *file,
>   	if (opts.mcount && sym->fentry) {
>   		if (sibling)
>   			WARN_FUNC("Tail call to __fentry__ !?!?", insn->sec, insn->offset);
> +		if (opts.mnop) {
> +			if (reloc) {
> +				reloc->type = R_NONE;
> +				elf_write_reloc(file->elf, reloc);
> +			}
>   
> -		if (reloc) {
> -			reloc->type = R_NONE;
> -			elf_write_reloc(file->elf, reloc);
> -		}
> -
> -		elf_write_insn(file->elf, insn->sec,
> -			       insn->offset, insn->len,
> -			       arch_nop_insn(insn->len));
> +			elf_write_insn(file->elf, insn->sec,
> +				       insn->offset, insn->len,
> +				       arch_nop_insn(insn->len));
>   
> -		insn->type = INSN_NOP;
> +			insn->type = INSN_NOP;
> +		}
>   
>   		list_add_tail(&insn->call_node, &file->mcount_loc_list);
>   		return;
> diff --git a/tools/objtool/include/objtool/builtin.h b/tools/objtool/include/objtool/builtin.h
> index 280ea18b7f2b..71ed3152a18e 100644
> --- a/tools/objtool/include/objtool/builtin.h
> +++ b/tools/objtool/include/objtool/builtin.h
> @@ -29,6 +29,7 @@ struct opts {
>   	bool backup;
>   	bool dryrun;
>   	bool link;
> +	bool mnop;
>   	bool module;
>   	bool no_unreachable;
>   	bool sec_address;