Re: [PATCH] powerpc: Fail build if using recordmcount with binutils v2.37

[Michael Ellerman <mpe@ellerman.id.au>]

Naveen N Rao <naveen@kernel.org> writes:
> binutils v2.37 drops unused section symbols, which prevents recordmcount
> from capturing mcount locations in sections that have no non-weak
> symbols. This results in a build failure with a message such as:
> 	Cannot find symbol for section 12: .text.perf_callchain_kernel.
> 	kernel/events/callchain.o: failed
>
> The change to binutils was reverted for v2.38, so this behavior is
> specific to binutils v2.37:
> https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=c09c8b42021180eee9495bd50d8b35e683d3901b
>
> Objtool is able to cope with such sections, so this issue is specific to
> recordmcount.
>
> Fail the build and print a warning if binutils v2.37 is detected and if
> we are using recordmcount.
>
> Cc: stable@vger.kernel.org
> Suggested-by: Joel Stanley <joel@jms.id.au>
> Signed-off-by: Naveen N Rao <naveen@kernel.org>
> ---
>  arch/powerpc/Makefile | 8 ++++++++
>  1 file changed, 8 insertions(+)
>
> diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile
> index dca73f673d7046..f0540c1f1377c8 100644
> --- a/arch/powerpc/Makefile
> +++ b/arch/powerpc/Makefile
> @@ -409,3 +409,11 @@ checkbin:
>  		echo -n '*** Please use a different binutils version.' ; \
>  		false ; \
>  	fi
> +	@if test "x${CONFIG_FTRACE_MCOUNT_USE_RECORDMCOUNT}" = "xy" -a \
> +		"x${CONFIG_LD_IS_BFD}" = "xy" -a \
> +		"x$(call ld-ifversion, -eq, 23700, y)" = "xy" ; then \
> +		echo -n '*** binutils 2.37 drops unused section symbols, which recordmcount ' ; \
> +		echo 'is unable to handle.' ; \
> +		echo '*** Please use a different binutils version.' ; \
> +		false ; \
> +	fi

Thanks for doing this.

Masahiro wanted to remove ld-ifversion, he suggested to just check
CONFIG_LD_VERSION directly instead. Mind doing a v2 with that change?

https://lore.kernel.org/all/CAK7LNAQWtDHOs=K+qznt5U1WiDv86tChkj4zOer4wtVRB974OA@mail.gmail.com/

cheers