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From: Alexander Bulekov <alxndr@bu.edu>
To: qemu-devel@nongnu.org
Cc: Alexander Bulekov <alxndr@bu.edu>, f4bug@amsat.org
Subject: [PATCH 2/4] fuzz: add an instrumentation filter
Date: Thu, 17 Jun 2021 15:53:51 -0400	[thread overview]
Message-ID: <20210617195353.284082-3-alxndr@bu.edu> (raw)
In-Reply-To: <20210617195353.284082-1-alxndr@bu.edu>

By default, -fsanitize=fuzzer instruments all code with coverage
information. However, this means that libfuzzer will track coverage over
hundreds of source files that are unrelated to virtual-devices. This
means that libfuzzer will optimize inputs for coverage observed in timer
code, memory APIs etc. This slows down the fuzzer and stores many inputs
that are not relevant to the actual virtual-devices.

With this change, clang will only instrument a subset of the compiled
code, that is directly related to virtual-devices.

Signed-off-by: Alexander Bulekov <alxndr@bu.edu>
---
 configure | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/configure b/configure
index debd50c085..40412bcfcf 100755
--- a/configure
+++ b/configure
@@ -6089,6 +6089,10 @@ if test "$fuzzing" = "yes" ; then
   # If LIB_FUZZING_ENGINE is set, assume we are running on OSS-Fuzz, and the
   # needed CFLAGS have already been provided
   if test -z "${LIB_FUZZING_ENGINE+xxx}" ; then
+    # Specify a filter to only instrument code that is directly related to
+    # virtual-devices.
+	QEMU_CFLAGS="$QEMU_CFLAGS -fsanitize-coverage-allowlist=$source_path/scripts/oss-fuzz/instrumentation-filter"
+
     # Add CFLAGS to tell clang to add fuzzer-related instrumentation to all the
     # compiled code.
     QEMU_CFLAGS="$QEMU_CFLAGS -fsanitize=fuzzer-no-link"
-- 
2.28.0



  parent reply	other threads:[~2021-06-17 19:56 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-17 19:53 [PATCH 0/4] Miscellaneous fuzzer changes Alexander Bulekov
2021-06-17 19:53 ` [PATCH 1/4] fuzz: adjust timeout to allow for longer inputs Alexander Bulekov
2021-06-17 19:53 ` Alexander Bulekov [this message]
2021-06-18  7:20   ` [PATCH 2/4] fuzz: add an instrumentation filter Philippe Mathieu-Daudé
2021-06-17 19:53 ` [PATCH 3/4] fuzz: fix the AC97 generic-fuzzer config Alexander Bulekov
2021-06-17 19:53 ` [PATCH 4/4] fuzz: fix the ES1370 " Alexander Bulekov

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