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From:   Dmitry Vyukov <dvyukov@gmail.com>
To:     akpm@linux-foundation.org
Cc:     Dmitry Vyukov <dvyukov@google.com>,
        Andrey Konovalov <andreyknvl@google.com>,
        kasan-dev@googlegroups.com, linux-kernel@vger.kernel.org
Subject: [PATCH] kcov: ignore fault-inject and stacktrace
Date:   Thu, 16 Jan 2020 12:14:49 +0100
Message-Id: <20200116111449.217744-1-dvyukov@gmail.com>
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Sender: linux-kernel-owner@vger.kernel.org
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From: Dmitry Vyukov <dvyukov@google.com>

Don't instrument 3 more files that contain debugging facilities and
produce large amounts of uninteresting coverage for every syscall.
The following snippets are sprinkled all over the place in kcov
traces in a debugging kernel. We already try to disable instrumentation
of stack unwinding code and of most debug facilities. I guess we
did not use fault-inject.c at the time, and stacktrace.c was somehow
missed (or something has changed in kernel/configs).
This change both speeds up kcov (kernel doesn't need to store these
PCs, user-space doesn't need to process them) and frees trace buffer
capacity for more useful coverage.

should_fail
lib/fault-inject.c:149
fail_dump
lib/fault-inject.c:45

stack_trace_save
kernel/stacktrace.c:124
stack_trace_consume_entry
kernel/stacktrace.c:86
stack_trace_consume_entry
kernel/stacktrace.c:89
... a hundred frames skipped ...
stack_trace_consume_entry
kernel/stacktrace.c:93
stack_trace_consume_entry
kernel/stacktrace.c:86

Signed-off-by: Dmitry Vyukov <dvyukov@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andrey Konovalov <andreyknvl@google.com>
Cc: kasan-dev@googlegroups.com
Cc: linux-kernel@vger.kernel.org
---
 kernel/Makefile | 1 +
 lib/Makefile    | 1 +
 mm/Makefile     | 1 +
 3 files changed, 3 insertions(+)

diff --git a/kernel/Makefile b/kernel/Makefile
index e5ffd8c002541..5d935b63f812a 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -30,6 +30,7 @@ KCSAN_SANITIZE_softirq.o = n
 # and produce insane amounts of uninteresting coverage.
 KCOV_INSTRUMENT_module.o := n
 KCOV_INSTRUMENT_extable.o := n
+KCOV_INSTRUMENT_stacktrace.o := n
 # Don't self-instrument.
 KCOV_INSTRUMENT_kcov.o := n
 KASAN_SANITIZE_kcov.o := n
diff --git a/lib/Makefile b/lib/Makefile
index 004a4642938af..6cd19bb3085c5 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -16,6 +16,7 @@ KCOV_INSTRUMENT_rbtree.o := n
 KCOV_INSTRUMENT_list_debug.o := n
 KCOV_INSTRUMENT_debugobjects.o := n
 KCOV_INSTRUMENT_dynamic_debug.o := n
+KCOV_INSTRUMENT_fault-inject.o := n
 
 # Early boot use of cmdline, don't instrument it
 ifdef CONFIG_AMD_MEM_ENCRYPT
diff --git a/mm/Makefile b/mm/Makefile
index 3c53198835479..c9696f3ec8408 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -28,6 +28,7 @@ KCOV_INSTRUMENT_kmemleak.o := n
 KCOV_INSTRUMENT_memcontrol.o := n
 KCOV_INSTRUMENT_mmzone.o := n
 KCOV_INSTRUMENT_vmstat.o := n
+KCOV_INSTRUMENT_failslab.o := n
 
 CFLAGS_init-mm.o += $(call cc-disable-warning, override-init)
 CFLAGS_init-mm.o += $(call cc-disable-warning, initializer-overrides)
-- 
2.25.0.rc1.283.g88dfdc4193-goog