Re: [PATCH 10/10] docs/fuzz: remove mentions of fork-based fuzzing

From: Darren Kenny <darren.kenny@oracle.com>
To: Alexander Bulekov <alxndr@bu.edu>, qemu-devel@nongnu.org
Cc: Alexander Bulekov <alxndr@bu.edu>,
	Stefan Hajnoczi <stefanha@redhat.com>,
	Bandan Das <bsd@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>,
	Thomas Huth <thuth@redhat.com>, Qiuhao Li <Qiuhao.Li@outlook.com>
Subject: Re: [PATCH 10/10] docs/fuzz: remove mentions of fork-based fuzzing
Date: Mon, 13 Feb 2023 14:48:37 +0000	[thread overview]
Message-ID: <m24jrpr58a.fsf@oracle.com> (raw)
In-Reply-To: <20230205042951.3570008-11-alxndr@bu.edu>

On Saturday, 2023-02-04 at 23:29:51 -05, Alexander Bulekov wrote:
> Signed-off-by: Alexander Bulekov <alxndr@bu.edu>

Reviewed-by: Darren Kenny <darren.kenny@oracle.com>

Thanks,

Darren.

> ---
>  docs/devel/fuzzing.rst | 22 ++--------------------
>  1 file changed, 2 insertions(+), 20 deletions(-)
>
> diff --git a/docs/devel/fuzzing.rst b/docs/devel/fuzzing.rst
> index 715330c856..3bfcb33fc4 100644
> --- a/docs/devel/fuzzing.rst
> +++ b/docs/devel/fuzzing.rst
> @@ -19,11 +19,6 @@ responsibility to ensure that state is reset between fuzzing-runs.
>  Building the fuzzers
>  --------------------
>  
> -*NOTE*: If possible, build a 32-bit binary. When forking, the 32-bit fuzzer is
> -much faster, since the page-map has a smaller size. This is due to the fact that
> -AddressSanitizer maps ~20TB of memory, as part of its detection. This results
> -in a large page-map, and a much slower ``fork()``.
> -
>  To build the fuzzers, install a recent version of clang:
>  Configure with (substitute the clang binaries with the version you installed).
>  Here, enable-sanitizers, is optional but it allows us to reliably detect bugs
> @@ -296,10 +291,9 @@ input. It is also responsible for manually calling ``main_loop_wait`` to ensure
>  that bottom halves are executed and any cleanup required before the next input.
>  
>  Since the same process is reused for many fuzzing runs, QEMU state needs to
> -be reset at the end of each run. There are currently two implemented
> -options for resetting state:
> +be reset at the end of each run. For example, this can be done by rebooting the
> +VM, after each run.
>  
> -- Reboot the guest between runs.
>    - *Pros*: Straightforward and fast for simple fuzz targets.
>  
>    - *Cons*: Depending on the device, does not reset all device state. If the
> @@ -308,15 +302,3 @@ options for resetting state:
>      reboot.
>  
>    - *Example target*: ``i440fx-qtest-reboot-fuzz``
> -
> -- Run each test case in a separate forked process and copy the coverage
> -   information back to the parent. This is fairly similar to AFL's "deferred"
> -   fork-server mode [3]
> -
> -  - *Pros*: Relatively fast. Devices only need to be initialized once. No need to
> -    do slow reboots or vmloads.
> -
> -  - *Cons*: Not officially supported by libfuzzer. Does not work well for
> -     devices that rely on dedicated threads.
> -
> -  - *Example target*: ``virtio-net-fork-fuzz``
> -- 
> 2.39.0