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

[George Dunlap <george.dunlap@xxxxxxxxxx>]

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@xxxxxxxxxx>
> 
> 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@xxxxxxxxxx>
>> CC: Wei Liu <wei.liu2@xxxxxxxxxx>
>> CC: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
>> CC: Jan Beulich <jbeulich@xxxxxxxx>
>> ---
>>  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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