linux-kernel - [PATCH RESEND v1 1/1] x86/kernel: Increase kcov coverage under arch/x86/kernel folder

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Date:   Mon, 31 Jul 2023 11:04:18 +0800
From:   Pengfei Xu <pengfei.xu@...el.com>
To:     dvyukov@...gle.com, nogikh@...gle.com, linux-kernel@...r.kernel.org
Cc:     Pengfei Xu <pengfei.xu@...el.com>, Heng Su <heng.su@...el.com>,
        syzkaller@...glegroups.com, keescook@...gle.com, mingo@...e.hu,
        Mehta Sohil <sohil.mehta@...el.com>,
        kirill.shutemov@...ux.intel.com, akpm@...ux-foundation.org
Subject: [PATCH RESEND v1 1/1] x86/kernel: Increase kcov coverage under arch/x86/kernel folder

Currently kcov instrument is disabled for object files under arch/x86/kernel
folder.
For object files under arch/x86/kernel, actually just disabling the kcov
instrument of files:"head32.o or head64.o and sev.o" could achieve
successful booting and provide kcov coverage for object files that do not
disable kcov instrument.
The additional kcov coverage collected from arch/x86/kernel folder helps
kernel fuzzing efforts to find bugs.

Link to related improvement discussion is below:
https://groups.google.com/g/syzkaller/c/Dsl-RYGCqs8/m/x-tfpTyFBAAJ
Related ticket is as follow:
https://bugzilla.kernel.org/show_bug.cgi?id=198443

Reviewed-by: Dmitry Vyukov <dvyukov@...gle.com>
Tested-by: Dmitry Vyukov <dvyukov@...gle.com>
Signed-off-by: Pengfei Xu <pengfei.xu@...el.com>
---
 arch/x86/kernel/Makefile | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index 4070a01c11b7..00df34c263cc 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -33,11 +33,10 @@ KCSAN_SANITIZE := n
 KMSAN_SANITIZE_head$(BITS).o				:= n
 KMSAN_SANITIZE_nmi.o					:= n
 
-# If instrumentation of this dir is enabled, boot hangs during first second.
-# Probably could be more selective here, but note that files related to irqs,
-# boot, dumpstack/stacktrace, etc are either non-interesting or can lead to
-# non-deterministic coverage.
-KCOV_INSTRUMENT		:= n
+# If instrumentation of the following files is enabled, boot hangs during
+# first second.
+KCOV_INSTRUMENT_head$(BITS).o				:= n
+KCOV_INSTRUMENT_sev.o					:= n
 
 CFLAGS_irq.o := -I $(srctree)/$(src)/../include/asm/trace
 
-- 
2.31.1