linux-kernel - Re: [PATCH v2 06/11] kcov: x86: introduce CONFIG_KCOV

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Message-ID: <20250627081146.GR1613200@noisy.programming.kicks-ass.net>
Date: Fri, 27 Jun 2025 10:11:46 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Alexander Potapenko <glider@...gle.com>
Cc: quic_jiangenj@...cinc.com, linux-kernel@...r.kernel.org,
	kasan-dev@...glegroups.com, x86@...nel.org,
	Aleksandr Nogikh <nogikh@...gle.com>,
	Andrey Konovalov <andreyknvl@...il.com>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Dmitry Vyukov <dvyukov@...gle.com>, Ingo Molnar <mingo@...hat.com>,
	Josh Poimboeuf <jpoimboe@...nel.org>,
	Marco Elver <elver@...gle.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v2 06/11] kcov: x86: introduce CONFIG_KCOV_UNIQUE

On Thu, Jun 26, 2025 at 03:41:53PM +0200, Alexander Potapenko wrote:
> The new config switches coverage instrumentation to using
>   __sanitizer_cov_trace_pc_guard(u32 *guard)
> instead of
>   __sanitizer_cov_trace_pc(void)
> 
> This relies on Clang's -fsanitize-coverage=trace-pc-guard flag [1].
> 
> Each callback receives a unique 32-bit guard variable residing in the
> __sancov_guards section. Those guards can be used by kcov to deduplicate
> the coverage on the fly.

This sounds like a *LOT* of data; how big is this for a typical kernel
build?