Subject: Re: [PATCH v2 2/2] powerpc: Enable kcov

From: Daniel Axtens <[email-masked]>
Date: Wed, 20 Feb 2019 15:26:33 +1100

Hi Andrew,

> kcov provides kernel coverage data that's useful for fuzzing tools like
> syzkaller.
>
> Wire up kcov support on powerpc. Disable kcov instrumentation on the same
> files where we currently disable gcov and UBSan instrumentation.
>
> Signed-off-by: Andrew Donnellan <[email-masked]>
> Acked-by: Dmitry Vyukov <[email-masked]>

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.

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.

With those changes,
Tested-by: Daniel Axtens <[email-masked]> # e6500

Regards,

> ---
>  arch/powerpc/Kconfig                | 1 +
>  arch/powerpc/kernel/Makefile        | 7 ++++++-
>  arch/powerpc/kernel/trace/Makefile  | 3 ++-
>  arch/powerpc/kernel/vdso32/Makefile | 1 +
>  arch/powerpc/kernel/vdso64/Makefile | 1 +
>  arch/powerpc/xmon/Makefile          | 1 +
>  6 files changed, 12 insertions(+), 2 deletions(-)
>
> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> index 2890d36eb531..d3698dae0e60 100644
> --- a/arch/powerpc/Kconfig
> +++ b/arch/powerpc/Kconfig
> @@ -134,6 +134,7 @@ config PPC
>  	select ARCH_HAS_ELF_RANDOMIZE
>  	select ARCH_HAS_FORTIFY_SOURCE
>  	select ARCH_HAS_GCOV_PROFILE_ALL
> +	select ARCH_HAS_KCOV
>  	select ARCH_HAS_PHYS_TO_DMA
>  	select ARCH_HAS_PMEM_API                if PPC64
>  	select ARCH_HAS_PTE_SPECIAL
> diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile
> index cb7f0bb9ee71..961f44eabb65 100644
> --- a/arch/powerpc/kernel/Makefile
> +++ b/arch/powerpc/kernel/Makefile
> @@ -142,16 +142,21 @@ endif
>  obj-$(CONFIG_EPAPR_PARAVIRT)	+= epapr_paravirt.o epapr_hcalls.o
>  obj-$(CONFIG_KVM_GUEST)		+= kvm.o kvm_emul.o
>  
> -# Disable GCOV & sanitizers in odd or sensitive code
> +# Disable GCOV, KCOV & sanitizers in odd or sensitive code
>  GCOV_PROFILE_prom_init.o := n
> +KCOV_INSTRUMENT_prom_init.o := n
>  UBSAN_SANITIZE_prom_init.o := n
>  GCOV_PROFILE_machine_kexec_64.o := n
> +KCOV_INSTRUMENT_machine_kexec_64.o := n
>  UBSAN_SANITIZE_machine_kexec_64.o := n
>  GCOV_PROFILE_machine_kexec_32.o := n
> +KCOV_INSTRUMENT_machine_kexec_32.o := n
>  UBSAN_SANITIZE_machine_kexec_32.o := n
>  GCOV_PROFILE_kprobes.o := n
> +KCOV_INSTRUMENT_kprobes.o := n
>  UBSAN_SANITIZE_kprobes.o := n
>  GCOV_PROFILE_kprobes-ftrace.o := n
> +KCOV_INSTRUMENT_kprobes-ftrace.o := n
>  UBSAN_SANITIZE_kprobes-ftrace.o := n
>  UBSAN_SANITIZE_vdso.o := n
>  
> diff --git a/arch/powerpc/kernel/trace/Makefile b/arch/powerpc/kernel/trace/Makefile
> index b1725ad3e13d..858503775c58 100644
> --- a/arch/powerpc/kernel/trace/Makefile
> +++ b/arch/powerpc/kernel/trace/Makefile
> @@ -23,6 +23,7 @@ obj-$(CONFIG_TRACING)			+= trace_clock.o
>  obj-$(CONFIG_PPC64)			+= $(obj64-y)
>  obj-$(CONFIG_PPC32)			+= $(obj32-y)
>  
> -# Disable GCOV & sanitizers in odd or sensitive code
> +# Disable GCOV, KCOV & sanitizers in odd or sensitive code
>  GCOV_PROFILE_ftrace.o := n
> +KCOV_INSTRUMENT_ftrace.o := n
>  UBSAN_SANITIZE_ftrace.o := n
> diff --git a/arch/powerpc/kernel/vdso32/Makefile b/arch/powerpc/kernel/vdso32/Makefile
> index 50112d4473bb..ce199f6e4256 100644
> --- a/arch/powerpc/kernel/vdso32/Makefile
> +++ b/arch/powerpc/kernel/vdso32/Makefile
> @@ -23,6 +23,7 @@ targets := $(obj-vdso32) vdso32.so vdso32.so.dbg
>  obj-vdso32 := $(addprefix $(obj)/, $(obj-vdso32))
>  
>  GCOV_PROFILE := n
> +KCOV_INSTRUMENT := n
>  UBSAN_SANITIZE := n
>  
>  ccflags-y := -shared -fno-common -fno-builtin
> diff --git a/arch/powerpc/kernel/vdso64/Makefile b/arch/powerpc/kernel/vdso64/Makefile
> index 69cecb346269..28e7d112aa2f 100644
> --- a/arch/powerpc/kernel/vdso64/Makefile
> +++ b/arch/powerpc/kernel/vdso64/Makefile
> @@ -9,6 +9,7 @@ targets := $(obj-vdso64) vdso64.so vdso64.so.dbg
>  obj-vdso64 := $(addprefix $(obj)/, $(obj-vdso64))
>  
>  GCOV_PROFILE := n
> +KCOV_INSTRUMENT := n
>  UBSAN_SANITIZE := n
>  
>  ccflags-y := -shared -fno-common -fno-builtin
> diff --git a/arch/powerpc/xmon/Makefile b/arch/powerpc/xmon/Makefile
> index 878f9c1d3615..3050f9323254 100644
> --- a/arch/powerpc/xmon/Makefile
> +++ b/arch/powerpc/xmon/Makefile
> @@ -5,6 +5,7 @@
>  subdir-ccflags-y := $(call cc-disable-warning, builtin-requires-header)
>  
>  GCOV_PROFILE := n
> +KCOV_INSTRUMENT := n
>  UBSAN_SANITIZE := n
>  
>  # Disable ftrace for the entire directory
> -- 
> 2.11.0