fuzz: add oss-fuzz build-script

It is neater to keep this in the QEMU repo, since any change that
requires an update to the oss-fuzz build configuration, can make the
necessary changes in the same series.

Suggested-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Alexander Bulekov <alxndr@bu.edu>
Reviewed-by: Darren Kenny <darren.kenny@oracle.com>
Message-Id: <20200612055145.12101-1-alxndr@bu.edu>
Signed-off-by: Thomas Huth <thuth@redhat.com>

MAINTAINERS

@@ -2339,6 +2339,7 @@ R: Bandan Das <bsd@redhat.com>
 R: Stefan Hajnoczi <stefanha@redhat.com>
 S: Maintained
 F: tests/qtest/fuzz/
+F: scripts/oss-fuzz/
 
 Register API
 M: Alistair Francis <alistair@alistair23.me>

scripts/oss-fuzz/build.sh

@@ -0,0 +1,105 @@
+#!/bin/sh -e
+#
+# OSS-Fuzz build script. See:
+# https://google.github.io/oss-fuzz/getting-started/new-project-guide/#buildsh
+#
+# The file is consumed by:
+# https://github.com/google/oss-fuzz/blob/master/projects/qemu/Dockerfiles
+#
+# This code is licensed under the GPL version 2 or later.  See
+# the COPYING file in the top-level directory.
+#
+
+# build project
+# e.g.
+# ./autogen.sh
+# ./configure
+# make -j$(nproc) all
+
+# build fuzzers
+# e.g.
+# $CXX $CXXFLAGS -std=c++11 -Iinclude \
+#     /path/to/name_of_fuzzer.cc -o $OUT/name_of_fuzzer \
+#     $LIB_FUZZING_ENGINE /path/to/library.a
+
+fatal () {
+    echo "Error : ${*}, exiting."
+    exit 1
+}
+
+OSS_FUZZ_BUILD_DIR="./build-oss-fuzz/"
+
+# There seems to be a bug in clang-11 (used for builds on oss-fuzz) :
+#   accel/tcg/cputlb.o: In function `load_memop':
+#   accel/tcg/cputlb.c:1505: undefined reference to `qemu_build_not_reached'
+#
+# When building with optimization, the compiler is expected to prove that the
+# statement cannot be reached, and remove it. For some reason clang-11 doesn't
+# remove it, resulting in an unresolved reference to qemu_build_not_reached
+# Undefine the __OPTIMIZE__ macro which compiler.h relies on to choose whether
+# to " #define qemu_build_not_reached()  g_assert_not_reached() "
+EXTRA_CFLAGS="$CFLAGS -U __OPTIMIZE__"
+
+if ! { [ -e "./COPYING" ] &&
+   [ -e "./MAINTAINERS" ] &&
+   [ -e "./Makefile" ] &&
+   [ -e "./docs" ] &&
+   [ -e "./VERSION" ] &&
+   [ -e "./linux-user" ] &&
+   [ -e "./softmmu" ];} ; then
+    fatal "Please run the script from the top of the QEMU tree"
+fi
+
+mkdir -p $OSS_FUZZ_BUILD_DIR || fatal "mkdir $OSS_FUZZ_BUILD_DIR failed"
+cd $OSS_FUZZ_BUILD_DIR || fatal "cd $OSS_FUZZ_BUILD_DIR failed"
+
+
+if [ -z ${LIB_FUZZING_ENGINE+x} ]; then
+    LIB_FUZZING_ENGINE="-fsanitize=fuzzer"
+fi
+
+if [ -z ${OUT+x} ]; then
+    DEST_DIR=$(realpath "./DEST_DIR")
+else
+    DEST_DIR=$OUT
+fi
+
+mkdir -p "$DEST_DIR/lib/"  # Copy the shared libraries here
+
+# Build once to get the list of dynamic lib paths, and copy them over
+../configure --disable-werror --cc="$CC" --cxx="$CXX" \
+    --extra-cflags="$EXTRA_CFLAGS"
+
+if ! make CONFIG_FUZZ=y CFLAGS="$LIB_FUZZING_ENGINE" "-j$(nproc)" \
+    i386-softmmu/fuzz; then
+    fatal "Build failed. Please specify a compiler with fuzzing support"\
+          "using the \$CC and \$CXX environemnt variables, or specify a"\
+          "\$LIB_FUZZING_ENGINE compatible with your compiler"\
+          "\nFor example: CC=clang CXX=clang++ $0"
+fi
+
+for i in $(ldd ./i386-softmmu/qemu-fuzz-i386 | cut -f3 -d' '); do
+    cp "$i" "$DEST_DIR/lib/"
+done
+rm ./i386-softmmu/qemu-fuzz-i386
+
+# Build a second time to build the final binary with correct rpath
+../configure --bindir="$DEST_DIR" --datadir="$DEST_DIR/data/" --disable-werror \
+    --cc="$CC" --cxx="$CXX" --extra-cflags="$EXTRA_CFLAGS" \
+    --extra-ldflags="-Wl,-rpath,'\$\$ORIGIN/lib'"
+make CONFIG_FUZZ=y CFLAGS="$LIB_FUZZING_ENGINE" "-j$(nproc)" i386-softmmu/fuzz
+
+# Copy over the datadir
+cp  -r ../pc-bios/ "$DEST_DIR/pc-bios"
+
+# Run the fuzzer with no arguments, to print the help-string and get the list
+# of available fuzz-targets. Copy over the qemu-fuzz-i386, naming it according
+# to each available fuzz target (See 05509c8e6d fuzz: select fuzz target using
+# executable name)
+for target in $(./i386-softmmu/qemu-fuzz-i386 | awk '$1 ~ /\*/  {print $2}');
+do
+    cp ./i386-softmmu/qemu-fuzz-i386 "$DEST_DIR/qemu-fuzz-i386-target-$target"
+done
+
+echo "Done. The fuzzers are located in $DEST_DIR"
+exit 0