Re: [PATCH 01/14] fuzz/x86_emulate: Remove redundant AFL hook

From: George Dunlap <george.dunlap@citrix.com>
To: Andrew Cooper <andrew.cooper3@citrix.com>,
	xen-devel <xen-devel@lists.xenproject.org>
Cc: Ian Jackson <ian.jackson@citrix.com>,
	Wei Liu <wei.liu2@citrix.com>, Jan Beulich <jbeulich@suse.com>
Subject: Re: [PATCH 01/14] fuzz/x86_emulate: Remove redundant AFL hook
Date: Thu, 14 Sep 2017 16:26:22 +0100	[thread overview]
Message-ID: <CAFLBxZa8fRkwrmx-FLNVzuHcS8rfB4vxMnNGzVcwj5Qx4MNx9A@mail.gmail.com> (raw)
In-Reply-To: <9fcd6e90-6b62-fdf1-7569-2f44b75b33e7@citrix.com>

Ping?

I realize this isn't a  major feature but it would be nice to get it
in for 4.10.

 -George

On Mon, Aug 28, 2017 at 11:34 AM, George Dunlap
<george.dunlap@citrix.com> wrote:
> On 08/25/2017 06:37 PM, Andrew Cooper wrote:
>> On 25/08/17 17:43, George Dunlap wrote:
>>> You don't need __AFL_INIT if you have __AFL_LOOP.
>>>
>>> Signed-off-by: George Dunlap <george.dunlap@citrix.com>
>>
>> Really?  Is that covered in any documentation?
>>
>> I got the contrary impression from whichever version of AFL I was using
>> when I put this in, and a quick look over the afl-fuzz source doesn't
>> appear to equate them in any way.
>
> The documentation does seem a bit hazy on the subject.  However:
>
> 1. It clear from the documentation [1] that both of them work *only* in
> llvm mode (i.e., when compiled with afl-clang-fast).  In particular the
> last paragraph of section 4: "afl-gcc or afl-clang will
> *not* generate a deferred-initialization binary".
>
> 2. The documentation does seem to speak of them as separate 'modes'
> (Section 5, "Note that as with the previous mode, ...")
>
> 3. Empirically speaking, persistent mode works fine with __AFL_LOOP()
> and no __AFL_INIT() (for me anyway).
>
>  -George
>
> [1] https://github.com/mirrorer/afl/tree/master/llvm_mode
>
>>
>> ~Andrew
>>
>>> ---
>>> CC: Ian Jackson <ian.jackson@citrix.com>
>>> CC: Wei Liu <wei.liu2@citrix.com>
>>> CC: Andrew Cooper <andrew.cooper3@citrix.com>
>>> CC: Jan Beulich <jbeulich@suse.com>
>>> ---
>>>  tools/fuzz/x86_instruction_emulator/afl-harness.c | 2 --
>>>  1 file changed, 2 deletions(-)
>>>
>>> diff --git a/tools/fuzz/x86_instruction_emulator/afl-harness.c b/tools/fuzz/x86_instruction_emulator/afl-harness.c
>>> index 154869336a..1a79ff228e 100644
>>> --- a/tools/fuzz/x86_instruction_emulator/afl-harness.c
>>> +++ b/tools/fuzz/x86_instruction_emulator/afl-harness.c
>>> @@ -63,8 +63,6 @@ int main(int argc, char **argv)
>>>          exit(-1);
>>>
>>>  #ifdef __AFL_HAVE_MANUAL_CONTROL
>>> -    __AFL_INIT();
>>> -
>>>      while ( __AFL_LOOP(1000) )
>>>  #endif
>>>      {
>>
>
>
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