Upgrade fuzzers to LIB_FUZZING_ENGINE

And check that LIB_FUZZING_ENGINE is set during configure.

Because:
1. It's easier to build locally this way (you don't need to build or hack a
libFuzzingEngine.a - instead you can just specify
LIB_FUZZING_ENGINE=-fsanitize=fuzzer to produce a valid build).
2. Using -lFuzzingEngine is deprecated [1] for various reasons [2].

The old behaviour can be emulated if desired by setting
LIB_FUZZING_ENGINE=-lFuzzingEngine .

This patch was tested as follows:
- Building LO within oss-fuzz via:
python infra/helper.py build_fuzzers --sanitizer address libreoffice </path/to/patched-libreoffice-core>
python infra/helper.py check_build libreoffice
- Building LO fuzzers standalone via:
export CC="clang-11"
export CXX="clang++-11 -stdlib=libc++"
export CFLAGS="-fsanitize=address -fsanitize-address-use-after-scope -fsanitize=fuzzer-no-link -DFUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION"
export CXXFLAGS="$CFLAGS -stdlib=libc++"
export LDFLAGS="$CFLAGS -Wl,--compress-debug-sections,zlib -lpthread"
export LIB_FUZZING_ENGINE=-fsanitize=fuzzer
./autogen.sh --with-distro=LibreOfficeOssFuzz  --with-system-libxml
make fuzzers
(--with-system-libxml only appears to be needed because of issues
specific to my build environment/Suse 15.2. I'm invoking clang-11 simply
because that's the most modern clang I have installed, plain clang should
also work on most sufficiently modern systems).

[1]
https://github.com/google/oss-fuzz/blob/481280c65048fd12fb2141b9225af511a9ef7ed2/infra/presubmit.py#L46
[2] https://github.com/google/oss-fuzz/issues/2164

Change-Id: Iddb577c30a39620e72372ef6c2d3fda67f8aabdf
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/111691
Tested-by: Jenkins
Tested-by: Caolán McNamara <caolanm@redhat.com>
Reviewed-by: Caolán McNamara <caolanm@redhat.com>

1 files changed, 4 insertions, 0 deletions

diff --git a/configure.ac b/configure.ac
index 9e0085370d2b..90b0cf01633b 100644
--- a/configure.ac
+++ b/configure.ac
@@ -10396,11 +10396,15 @@ AC_MSG_CHECKING([whether to enable fuzzers])
 if test "$enable_fuzzers" != yes; then
     AC_MSG_RESULT([no])
 else
+    if test $LIB_FUZZING_ENGINE == ""; then
+      AC_MSG_ERROR(['LIB_FUZZING_ENGINE' must be set when using --enable-fuzzers. Examples include '-fsanitize=fuzzer'.])
+    fi
     AC_MSG_RESULT([yes])
     ENABLE_FUZZERS="TRUE"
     AC_DEFINE([ENABLE_FUZZERS],1)
     BUILD_TYPE="$BUILD_TYPE FUZZERS"
 fi
+AC_SUBST(LIB_FUZZING_ENGINE)
 AC_SUBST(ENABLE_FUZZERS)
 
 dnl ===================================================================