linux-kernel - [PATCH 0/5] kcov: PREEMPT

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Message-Id: <20210830172627.267989-1-bigeasy@linutronix.de>
Date:   Mon, 30 Aug 2021 19:26:22 +0200
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     kasan-dev@...glegroups.com, linux-kernel@...r.kernel.org
Cc:     Dmitry Vyukov <dvyukov@...gle.com>,
        Andrey Konovalov <andreyknvl@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Steven Rostedt <rostedt@...dmis.org>,
        Marco Elver <elver@...gle.com>,
        Clark Williams <williams@...hat.com>
Subject: [PATCH 0/5] kcov: PREEMPT_RT fixup + misc

The last patch in series is follow-up to address the PREEMPT_RT issue
within in kcov reported by Clark [0].
Patches 1-3 are smaller things that I noticed while staring at it.
Patch 4 is small change which makes replacement in #5 simpler / more
obvious.
I tested this with the three examples in the documentation folder and I
didn't notice higher latency with kcov enabled. Debug or not, I don't
see a reason to make the lock a raw_spin_lock_t annd it would complicate
memory allocation as mentioned in #5.

One thing I noticed and have no idea if this is right or not:
The code seems to mix long and uint64_t for the reported instruction
pointer / position in the buffer. For instance
__sanitizer_cov_trace_pc() refers to a 64bit pointer (in the comment)
while the area pointer itself is (long *). The problematic part is that
a 32bit application on a 64bit pointer will expect a four byte pointer
while kernel uses an eight byte pointer.

[0] https://lkml.kernel.org/r/20210809155909.333073de@theseus.lan

Sebastian