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Subject: Re: [PATCH v2 2/2] powerpc: Enable kcov
To: Daniel Axtens <dja@axtens.net>, linuxppc-dev@lists.ozlabs.org
References: <20190211002002.26038-1-andrew.donnellan@au1.ibm.com>
 <20190211002002.26038-2-andrew.donnellan@au1.ibm.com>
 <87o9772ih2.fsf@dja-thinkpad.axtens.net>
From: Andrew Donnellan <andrew.donnellan@au1.ibm.com>
Date: Wed, 20 Feb 2019 15:47:27 +1100
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On 20/2/19 3:26 pm, Daniel Axtens wrote:
> I needed the following diff to get this booting on a T4240RDB:
> 
> diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile
> index 961f44eabb65..fbe9894d6305 100644
> --- a/arch/powerpc/kernel/Makefile
> +++ b/arch/powerpc/kernel/Makefile
> @@ -3,6 +3,10 @@
>   # Makefile for the linux kernel.
>   #
>   
> +KCOV_INSTRUMENT_cputable.o := n
> +KCOV_INSTRUMENT_setup_64.o := n
> +KCOV_INSTRUMENT_paca.o := n
> +
>   CFLAGS_ptrace.o                += -DUTS_MACHINE='"$(UTS_MACHINE)"'
>   
>   # Disable clang warning for using setjmp without setjmp.h header
> diff --git a/arch/powerpc/mm/Makefile b/arch/powerpc/mm/Makefile
> index f965fc33a8b7..0140e7e12c29 100644
> --- a/arch/powerpc/mm/Makefile
> +++ b/arch/powerpc/mm/Makefile
> @@ -5,6 +5,9 @@
>   
>   ccflags-$(CONFIG_PPC64)        := $(NO_MINIMAL_TOC)
>   
> +KCOV_INSTRUMENT_tlb_nohash.o := n
> +KCOV_INSTRUMENT_fsl_booke_mmu.o := n
> +
>   CFLAGS_REMOVE_slb.o = $(CC_FLAGS_FTRACE)
>   
>   obj-y                          := fault.o mem.o pgtable.o mmap.o \
> 
> 
> The change to kernel/ is required to get the kernel to even begin to
> boot, and the change to mm/ is required to successfully set up SMP. I'm
> not sure preciesly why they cause issues.

Thanks for testing this - I'll roll this into v3.

> 
> I was then able to run kcovtrace and the results seem to make sense. >
> Perhaps in the future some further stuff should be trimmed down to make
> the coverage results less noisy (restore_math is probably not telling us
> anything interesting, for example), but certainly this is a great start.

I think syzkaller (as the main kcov consumer) can probably cope...

> 
> With those changes,
> Tested-by: Daniel Axtens <dja@axtens.net> # e6500


-- 
Andrew Donnellan              OzLabs, ADL Canberra
andrew.donnellan@au1.ibm.com  IBM Australia Limited