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envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Received-SPF: pass client-ip=40.107.93.119; envelope-from=alxndr@bu.edu; helo=NAM10-DM6-obe.outbound.protection.outlook.com X-Spam_score_int: -8 X-Spam_score: -0.9 X-Spam_bar: / X-Spam_report: (-0.9 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, HK_RANDOM_ENVFROM=0.001, HK_RANDOM_FROM=0.998, MSGID_FROM_MTA_HEADER=0.001, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=no autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Paolo Bonzini , Darren Kenny , Alexander Bulekov Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" X-ZohoMail-DKIM: pass (identity @bushare.onmicrosoft.com) X-ZM-MESSAGEID: 1626188710607100001 Content-Type: text/plain; charset="utf-8" By default, -fsanitize=3Dfuzzer 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 versions that support the "-fsanitize-coverage-allowlist" will only instrument a subset of the compiled code, that is directly related to virtual-devices. Signed-off-by: Alexander Bulekov Reviewed-by: Darren Kenny --- configure | 28 +++++++++++++++---- .../oss-fuzz/instrumentation-filter-template | 15 ++++++++++ 2 files changed, 37 insertions(+), 6 deletions(-) create mode 100644 scripts/oss-fuzz/instrumentation-filter-template diff --git a/configure b/configure index e799d908a3..99d6182af9 100755 --- a/configure +++ b/configure @@ -4943,13 +4943,21 @@ fi =20 ########################################## # checks for fuzzer -if test "$fuzzing" =3D "yes" && test -z "${LIB_FUZZING_ENGINE+xxx}"; then +if test "$fuzzing" =3D "yes" ; then write_c_fuzzer_skeleton - if compile_prog "$CPU_CFLAGS -Werror -fsanitize=3Dfuzzer" ""; then - have_fuzzer=3Dyes - else - error_exit "Your compiler doesn't support -fsanitize=3Dfuzzer" - exit 1 + if test -z "${LIB_FUZZING_ENGINE+xxx}"; then + if compile_prog "$CPU_CFLAGS -Werror -fsanitize=3Dfuzzer" ""; then + have_fuzzer=3Dyes + else + error_exit "Your compiler doesn't support -fsanitize=3Dfuzzer" + exit 1 + fi + fi + + have_clang_coverage_filter=3Dno + echo > $TMPTXT + if compile_prog "$CPU_CFLAGS -Werror -fsanitize=3Dfuzzer -fsanitize-cove= rage-allowlist=3D$TMPTXT" ""; then + have_clang_coverage_filter=3Dyes fi fi =20 @@ -5843,6 +5851,14 @@ if test "$fuzzing" =3D "yes" ; then else FUZZ_EXE_LDFLAGS=3D"$LIB_FUZZING_ENGINE" fi + + # Specify a filter to only instrument code that is directly related to + # virtual-devices. + if test "$have_clang_coverage_filter" =3D "yes" ; then + cp "$source_path/scripts/oss-fuzz/instrumentation-filter-template" \ + instrumentation-filter + QEMU_CFLAGS=3D"$QEMU_CFLAGS -fsanitize-coverage-allowlist=3Dinstrument= ation-filter" + fi fi =20 if test "$plugins" =3D "yes" ; then diff --git a/scripts/oss-fuzz/instrumentation-filter-template b/scripts/oss= -fuzz/instrumentation-filter-template new file mode 100644 index 0000000000..76d2b6139a --- /dev/null +++ b/scripts/oss-fuzz/instrumentation-filter-template @@ -0,0 +1,15 @@ +# Code that we actually want the fuzzer to target +# See: https://clang.llvm.org/docs/SanitizerCoverage.html#disabling-instru= mentation-without-source-modification +# +src:*/hw/* +src:*/include/hw/* +src:*/slirp/* +src:*/net/* + +# We don't care about coverage over fuzzer-specific code, however we should +# instrument the fuzzer entry-point so libFuzzer always sees at least some +# coverage - otherwise it will exit after the first input +src:*/tests/qtest/fuzz/fuzz.c + +# Enable instrumentation for all functions in those files +fun:* --=20 2.28.0