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Date:   Fri, 25 Mar 2022 13:46:29 -0700
From:   Andrew Morton <akpm@linux-foundation.org>
To:     andrey.konovalov@linux.dev
Cc:     Marco Elver <elver@google.com>,
        Alexander Potapenko <glider@google.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
        Andrey Konovalov <andreyknvl@gmail.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Andrey Ryabinin <ryabinin.a.a@gmail.com>,
        kasan-dev@googlegroups.com, Mark Rutland <mark.rutland@arm.com>,
        Vincenzo Frascino <vincenzo.frascino@arm.com>,
        Sami Tolvanen <samitolvanen@google.com>,
        Peter Collingbourne <pcc@google.com>,
        Evgenii Stepanov <eugenis@google.com>,
        Florian Mayer <fmayer@google.com>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org,
        Andrey Konovalov <andreyknvl@google.com>
Subject: Re: [PATCH v2 1/4] stacktrace: add interface based on shadow call
 stack
Message-Id: <20220325134629.99699c921bb8c8db413e8e35@linux-foundation.org>
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        <21e3e20ea58e242e3c82c19abbfe65b579e0e4b8.1648049113.git.andreyknvl@google.com>
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On Wed, 23 Mar 2022 16:32:52 +0100 andrey.konovalov@linux.dev wrote:

> From: Andrey Konovalov <andreyknvl@google.com>
> 
> Add a new interface stack_trace_save_shadow() for collecting stack traces
> by copying frames from the Shadow Call Stack.
> 
> Collecting stack traces this way is significantly faster: boot time
> of a defconfig build with KASAN enabled gets descreased by ~30%.
> 
> The few patches following this one add an implementation of
> stack_trace_save_shadow() for arm64.
> 
> The implementation of the added interface is not meant to use
> stack_trace_consume_fn to avoid making a function call for each
> collected frame to further improve performance.
> 
> ...
>
> @@ -108,4 +111,16 @@ static inline int stack_trace_save_tsk_reliable(struct task_struct *tsk,
>  }
>  #endif
>  
> +#if defined(CONFIG_STACKTRACE) && defined(CONFIG_HAVE_SHADOW_STACKTRACE)
> +int stack_trace_save_shadow(unsigned long *store, unsigned int size,
> +			    unsigned int skipnr);
> +#else
> +static inline int stack_trace_save_shadow(unsigned long *store,
> +					  unsigned int size,
> +					  unsigned int skipnr)
> +{
> +	return -ENOSYS;
> +}
> +#endif

checkpatch sayeth "WARNING: ENOSYS means 'invalid syscall nr' and
nothing else".

checkpatch also picked up a typo in a changelog.  Useful thing to run,
is checkpatch.