[PULL 44/46] fuzz: Add support for custom fuzzing library

[Paolo Bonzini <pbonzini@redhat.com>]

From: Alexander Bulekov <alxndr@bu.edu>

On oss-fuzz, we must use the LIB_FUZZING_ENGINE and CFLAGS environment
variables, rather than -fsanitize=fuzzer. With this change, when
LIB_FUZZING_ENGINE is set, the --enable-fuzzing configure option will
use that environment variable during the linking stage, rather than
-fsanitize=fuzzer

Signed-off-by: Alexander Bulekov <alxndr@bu.edu>
Message-Id: <20200902173652.307222-3-alxndr@bu.edu>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 configure                    | 12 ++++++++++--
 tests/qtest/fuzz/meson.build |  4 ++--
 2 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/configure b/configure
index c71bceb8e8..d3495e107f 100755
--- a/configure
+++ b/configure
@@ -6023,7 +6023,7 @@ fi
 
 ##########################################
 # checks for fuzzer
-if test "$fuzzing" = "yes" ; then
+if test "$fuzzing" = "yes" && test -z "${LIB_FUZZING_ENGINE+xxx}"; then
   write_c_fuzzer_skeleton
   if compile_prog "$CPU_CFLAGS -Werror -fsanitize=fuzzer" ""; then
     have_fuzzer=yes
@@ -7291,7 +7291,14 @@ if test "$have_mlockall" = "yes" ; then
   echo "HAVE_MLOCKALL=y" >> $config_host_mak
 fi
 if test "$fuzzing" = "yes" ; then
-  QEMU_CFLAGS="$QEMU_CFLAGS -fsanitize=fuzzer-no-link"
+  # If LIB_FUZZING_ENGINE is set, assume we are running on OSS-Fuzz, and the
+  # needed CFLAGS have already been provided
+  if test -z "${LIB_FUZZING_ENGINE+xxx}" ; then
+    QEMU_CFLAGS="$QEMU_CFLAGS -fsanitize=fuzzer-no-link"
+    FUZZ_EXE_LDFLAGS="-fsanitize=fuzzer"
+  else
+    FUZZ_EXE_LDFLAGS="$LIB_FUZZING_ENGINE"
+  fi
 fi
 
 if test "$plugins" = "yes" ; then
@@ -7392,6 +7399,7 @@ fi
 if test "$fuzzing" != "no"; then
     echo "CONFIG_FUZZ=y" >> $config_host_mak
 fi
+echo "FUZZ_EXE_LDFLAGS=$FUZZ_EXE_LDFLAGS" >> $config_host_mak
 
 if test "$edk2_blobs" = "yes" ; then
   echo "DECOMPRESS_EDK2_BLOBS=y" >> $config_host_mak
diff --git a/tests/qtest/fuzz/meson.build b/tests/qtest/fuzz/meson.build
index bcc393828e..b31ace7d5a 100644
--- a/tests/qtest/fuzz/meson.build
+++ b/tests/qtest/fuzz/meson.build
@@ -7,8 +7,8 @@ specific_fuzz_ss.add(when: 'CONFIG_VIRTIO_NET', if_true: files('virtio_net_fuzz.
 specific_fuzz_ss.add(when: 'CONFIG_VIRTIO_SCSI', if_true: files('virtio_scsi_fuzz.c'))
 
 fork_fuzz = declare_dependency(
-  link_args: ['-fsanitize=fuzzer',
-              '-Wl,-wrap,qtest_inb',
+  link_args: config_host['FUZZ_EXE_LDFLAGS'].split() +
+             ['-Wl,-wrap,qtest_inb',
               '-Wl,-wrap,qtest_inw',
               '-Wl,-wrap,qtest_inl',
               '-Wl,-wrap,qtest_outb',
-- 
2.26.2