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

[Naveen N Rao <naveen@kernel.org>]

Michael Ellerman wrote:
> 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/

I have posted a v2 with just that change. Let me know if you are 
planning to pick up Masahiro's patch above and if you want me to base my 
changes atop that (just have to add back archprepare/checkbin).


- Naveen