Re: [uml-devel] [PATCH] um: Fix kcov crash before kernel is started.

[Anton Ivanov]

On 14/10/17 09:05, Richard Weinberger wrote:
> Am Samstag, 14. Oktober 2017, 00:00:25 CEST schrieb Thomas Meyer:
>> UMLs current_thread_info() unconditionally assumes that the top of the stack
>> contains the thread_info structure.
>> Prevent kcov from using invalid curent_thread_info() data by disable
>> instrumentation of early startup code.
>>
>> Signed-off-by: Thomas Meyer 
>> ---
>>  arch/um/kernel/skas/Makefile | 2 ++
>>  lib/Makefile | 4 
>>  2 files changed, 6 insertions(+)
>>
>> diff --git a/arch/um/kernel/skas/Makefile b/arch/um/kernel/skas/Makefile
>> index 0b76d8869c94..df3aedb974a2 100644
>> --- a/arch/um/kernel/skas/Makefile
>> +++ b/arch/um/kernel/skas/Makefile
>> @@ -3,6 +3,8 @@
>>  # Licensed under the GPL
>>  #
>>
>> +KCOV_INSTRUMENT:= n
> So, you disable kconv for the whole SKAS code?
> That's a bit broad. ;-\

It is a part of UML which most of us approach with a distinct feeling of
dread. At least I do.

It may be worth it to do that in first instance and then try to narrow
down sections which can have it later on :)

A.

>
>>  obj-y := clone.o mmu.o process.o syscall.o uaccess.o
>>
>>  # clone.o is in the stub, so it can't be built with profiling
>> diff --git a/lib/Makefile b/lib/Makefile
>> index dafa79613fb4..18319ad5daab 100644
>> --- a/lib/Makefile
>> +++ b/lib/Makefile
>> @@ -16,6 +16,10 @@ KCOV_INSTRUMENT_list_debug.o := n
>>  KCOV_INSTRUMENT_debugobjects.o := n
>>  KCOV_INSTRUMENT_dynamic_debug.o := n
>>
>> +ifdef CONFIG_UML
>> +KCOV_INSTRUMENT_cmdline.o := n
>> +endif
>> +
> huh? Why do we need an exception for UML here?
>
> Thanks,
> //richard
>
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Re: [uml-devel] [PATCH] um: Fix kcov crash before kernel is started.

[Richard Weinberger]

Am Samstag, 14. Oktober 2017, 00:00:25 CEST schrieb Thomas Meyer:
> UMLs current_thread_info() unconditionally assumes that the top of the stack
> contains the thread_info structure.
> Prevent kcov from using invalid curent_thread_info() data by disable
> instrumentation of early startup code.
> 
> Signed-off-by: Thomas Meyer 
> ---
>  arch/um/kernel/skas/Makefile | 2 ++
>  lib/Makefile | 4 
>  2 files changed, 6 insertions(+)
> 
> diff --git a/arch/um/kernel/skas/Makefile b/arch/um/kernel/skas/Makefile
> index 0b76d8869c94..df3aedb974a2 100644
> --- a/arch/um/kernel/skas/Makefile
> +++ b/arch/um/kernel/skas/Makefile
> @@ -3,6 +3,8 @@
>  # Licensed under the GPL
>  #
> 
> +KCOV_INSTRUMENT:= n

So, you disable kconv for the whole SKAS code?
That's a bit broad. ;-\

>  obj-y := clone.o mmu.o process.o syscall.o uaccess.o
> 
>  # clone.o is in the stub, so it can't be built with profiling
> diff --git a/lib/Makefile b/lib/Makefile
> index dafa79613fb4..18319ad5daab 100644
> --- a/lib/Makefile
> +++ b/lib/Makefile
> @@ -16,6 +16,10 @@ KCOV_INSTRUMENT_list_debug.o := n
>  KCOV_INSTRUMENT_debugobjects.o := n
>  KCOV_INSTRUMENT_dynamic_debug.o := n
> 
> +ifdef CONFIG_UML
> +KCOV_INSTRUMENT_cmdline.o := n
> +endif
> +

huh? Why do we need an exception for UML here?

Thanks,
//richard

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Re: [uml-devel] [PATCH] um: Fix kcov crash before kernel is started.

[Richard Weinberger]

Am Sonntag, 8. Oktober 2017, 12:31:58 CEST schrieb Thomas Meyer:
> UMLs current_thread_info() unconditionally assumes that the top of the stack
> contains the thread_info structure. But on UML the __sanitizer_cov_trace_pc
> function is called for *all* functions! This results in an early crash:
> 
> Prevent kcov from using invalid curent_thread_info() data by checking
> the system_state.
> 
> Signed-off-by: Thomas Meyer 
> ---
>  kernel/kcov.c | 6 ++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/kernel/kcov.c b/kernel/kcov.c
> index 3f693a0f6f3e..d601c0e956f6 100644
> --- a/kernel/kcov.c
> +++ b/kernel/kcov.c
> @@ -56,6 +56,12 @@ void notrace __sanitizer_cov_trace_pc(void)
>   struct task_struct *t;
>   enum kcov_mode mode;
> 
> +#ifdef CONFIG_UML
> + if(!(system_state == SYSTEM_SCHEDULING ||
> +  system_state == SYSTEM_RUNNING))
> + return;
> +#endif

Hmm, and why does it work on all other archs then?

Thanks,
//richard


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