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Re: [PATCH v2] configure: fix --enable-fuzzing linker failures

From: Thomas Huth
Subject: Re: [PATCH v2] configure: fix --enable-fuzzing linker failures
Date: Mon, 22 Feb 2021 06:44:30 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.0

On 21/02/2021 18.45, Alexander Bulekov wrote:
With --enable-fuzzing, QEMU_CFLAGS include -fsanitize=fuzzer-no-link.
This should allow us to build non-fuzzer binaries using objects
instrumented for fuzzing. However, to do that, we also need to link with
-fsanitize=fuzzer-no-link. We were not doing that.

Reported-by: Li Qiang <liq3ea@163.com>,
Signed-off-by: Alexander Bulekov <alxndr@bu.edu>
v2: Fix a mistake in the added QEMU_LDFLAGS line

  configure | 10 ++++++++++
  1 file changed, 10 insertions(+)

diff --git a/configure b/configure
index a79b3746d4..19f2b88589 100755
--- a/configure
+++ b/configure
@@ -6096,7 +6096,17 @@ 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
+    # Add CFLAGS to tell clang to add fuzzer-related instrumentation to all the
+    # compiled code.
      QEMU_CFLAGS="$QEMU_CFLAGS -fsanitize=fuzzer-no-link"
+    # To build non-fuzzer binaries with --enable-fuzzing, link everything with
+    # fsanitize=fuzzer-no-link. Otherwise, the linker will be unable to bind
+    # the fuzzer-related callbacks added by instrumentation.
+    QEMU_LDFLAGS="$QEMU_LDFLAGS -fsanitize=fuzzer-no-link"
+    # For the actual fuzzer binaries, we need to link against the libfuzzer
+    # library. Provide the flags for doing this in FUZZ_EXE_LDFLAGS. The meson
+    # rule for the fuzzer adds these to the link_args. They need to be
+    # configurable, to support OSS-Fuzz

Reviewed-by: Thomas Huth <thuth@redhat.com>

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