Merge remote-tracking branch 'remotes/bonzini-gitlab/tags/for-upstream' into staging

* add --enable/--disable-libgio to configure (Denis)
* small fixes (Pavel, myself)
* fuzzing update (Alexander)

# gpg: Signature made Tue 16 Mar 2021 18:30:38 GMT
# gpg:                using RSA key F13338574B662389866C7682BFFBD25F78C7AE83
# gpg:                issuer "pbonzini@redhat.com"
# gpg: Good signature from "Paolo Bonzini <bonzini@gnu.org>" [full]
# gpg:                 aka "Paolo Bonzini <pbonzini@redhat.com>" [full]
# Primary key fingerprint: 46F5 9FBD 57D6 12E7 BFD4  E2F7 7E15 100C CD36 69B1
#      Subkey fingerprint: F133 3857 4B66 2389 866C  7682 BFFB D25F 78C7 AE83

* remotes/bonzini-gitlab/tags/for-upstream:
  qemu-timer: allow freeing a NULL timer
  hw/i8254: fix vmstate load
  scsi: fix sense code for EREMOTEIO
  Revert "accel: kvm: Add aligment assert for kvm_log_clear_one_slot"
  configure: add option to explicitly enable/disable libgio
  fuzz: move some DMA hooks
  fuzz: configure a sparse-mem device, by default
  memory: add a sparse memory device for fuzzing
  fuzz: add a am53c974 generic-fuzzer config
  fuzz: add instructions for building reproducers
  fuzz: add a script to build reproducers
  fuzz: don't leave orphan llvm-symbolizers around
  fuzz: fix the pro100 generic-fuzzer config
  MAINTAINERS: Cover fuzzer reproducer tests within 'Device Fuzzing'
  tests/qtest: Only run fuzz-virtio-scsi when virtio-scsi is available
  tests/qtest: Only run fuzz-megasas-test if megasas device is available

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

1 files changed, 56 insertions, 0 deletions

diff --git a/docs/devel/fuzzing.rst b/docs/devel/fuzzing.rst
index 97797c4f8c..2749bb9bed 100644
--- a/docs/devel/fuzzing.rst
+++ b/docs/devel/fuzzing.rst
@@ -210,6 +210,62 @@ Build details:
 - The script responsible for building the fuzzers can be found in the
   QEMU source tree at ``scripts/oss-fuzz/build.sh``
 
+Building Crash Reproducers
+-----------------------------------------
+When we find a crash, we should try to create an independent reproducer, that
+can be used on a non-fuzzer build of QEMU. This filters out any potential
+false-positives, and improves the debugging experience for developers.
+Here are the steps for building a reproducer for a crash found by the
+generic-fuzz target.
+
+- Ensure the crash reproduces::
+
+    qemu-fuzz-i386 --fuzz-target... ./crash-...
+
+- Gather the QTest output for the crash::
+
+    QEMU_FUZZ_TIMEOUT=0 QTEST_LOG=1 FUZZ_SERIALIZE_QTEST=1 \
+    qemu-fuzz-i386 --fuzz-target... ./crash-... &> /tmp/trace
+
+- Reorder and clean-up the resulting trace::
+
+    scripts/oss-fuzz/reorder_fuzzer_qtest_trace.py /tmp/trace > /tmp/reproducer
+
+- Get the arguments needed to start qemu, and provide a path to qemu::
+
+    less /tmp/trace # The args should be logged at the top of this file
+    export QEMU_ARGS="-machine ..."
+    export QEMU_PATH="path/to/qemu-system"
+
+- Ensure the crash reproduces in qemu-system::
+
+    $QEMU_PATH $QEMU_ARGS -qtest stdio < /tmp/reproducer
+
+- From the crash output, obtain some string that identifies the crash. This
+  can be a line in the stack-trace, for example::
+
+    export CRASH_TOKEN="hw/usb/hcd-xhci.c:1865"
+
+- Minimize the reproducer::
+
+    scripts/oss-fuzz/minimize_qtest_trace.py -M1 -M2 \
+      /tmp/reproducer /tmp/reproducer-minimized
+
+- Confirm that the minimized reproducer still crashes::
+
+    $QEMU_PATH $QEMU_ARGS -qtest stdio < /tmp/reproducer-minimized
+
+- Create a one-liner reproducer that can be sent over email::
+
+    ./scripts/oss-fuzz/output_reproducer.py -bash /tmp/reproducer-minimized
+
+- Output the C source code for a test case that will reproduce the bug::
+
+    ./scripts/oss-fuzz/output_reproducer.py -owner "John Smith <john@smith.com>"\
+      -name "test_function_name" /tmp/reproducer-minimized
+
+- Report the bug and send a patch with the C reproducer upstream
+
 Implementation Details / Fuzzer Lifecycle
 -----------------------------------------