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Subject: Re: [PATCH 2/2] riscv: Add KASAN support
To:     Nick Hu <nickhu@andestech.com>,
        Christoph Hellwig <hch@infradead.org>
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On 8/14/19 10:44 AM, Nick Hu wrote:

>>
>>> diff --git a/arch/riscv/kernel/vmlinux.lds.S b/arch/riscv/kernel/vmlinux.lds.S
>>> index 23cd1a9..9700980 100644
>>> --- a/arch/riscv/kernel/vmlinux.lds.S
>>> +++ b/arch/riscv/kernel/vmlinux.lds.S
>>> @@ -46,6 +46,7 @@ SECTIONS
>>>  		KPROBES_TEXT
>>>  		ENTRY_TEXT
>>>  		IRQENTRY_TEXT
>>> +		SOFTIRQENTRY_TEXT
>>
>> Hmm.  What is the relation to kasan here?  Maybe we should add this
>> separately with a good changelog?
>>
> There is a commit for it:
> 
> Author: Alexander Potapenko <glider@google.com>
> Date:   Fri Mar 25 14:22:05 2016 -0700
> 
>     arch, ftrace: for KASAN put hard/soft IRQ entries into separate sections
> 
>     KASAN needs to know whether the allocation happens in an IRQ handler.
>     This lets us strip everything below the IRQ entry point to reduce the
>     number of unique stack traces needed to be stored.
> 
>     Move the definition of __irq_entry to <linux/interrupt.h> so that the
>     users don't need to pull in <linux/ftrace.h>.  Also introduce the
>     __softirq_entry macro which is similar to __irq_entry, but puts the
>     corresponding functions to the .softirqentry.text section.
> 
> After reading the patch I understand that soft/hard IRQ entries should be
> separated for KASAN to work, but why?
> 

KASAN doesn't need soft/hard IRQ entries separated. KASAN wants to know the entry
point of IRQ (hard or soft) to filter out random non-irq part of the stacktrace before feeding it to
stack_depot_save. See filter_irq_stacks().