[llvm] r254558 - Libfuzzer: do not pass null into user function

[Mike Aizatsky via llvm-commits]

We don't want to enforce this contract on user fuzzer functions. While some
people find it reasonable, other prefer to add assert(ptr) to their code.


On Wed, Dec 2, 2015 at 9:39 PM David Blaikie <dblaikie at gmail.com> wrote:

> I think maybe this came up in the code review, but I'm still confused:
>
> Why is it significant to make the Data pointer non-null if the size is
> zero? The implementation shouldn't care what value the Data pointer has if
> it's been told that it points to zero valid bytes, no?
>
>
> On Wed, Dec 2, 2015 at 2:43 PM, Mike Aizatsky via llvm-commits <
> llvm-commits at lists.llvm.org> wrote:
>
>> Author: aizatsky
>> Date: Wed Dec  2 16:43:53 2015
>> New Revision: 254558
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=254558&view=rev
>> Log:
>> Libfuzzer: do not pass null into user function
>>
>> Differential Revision: http://reviews.llvm.org/D15098
>>
>> Modified:
>>     llvm/trunk/lib/Fuzzer/FuzzerLoop.cpp
>>     llvm/trunk/lib/Fuzzer/test/SimpleTest.cpp
>>
>> Modified: llvm/trunk/lib/Fuzzer/FuzzerLoop.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Fuzzer/FuzzerLoop.cpp?rev=254558&r1=254557&r2=254558&view=diff
>>
>> ==============================================================================
>> --- llvm/trunk/lib/Fuzzer/FuzzerLoop.cpp (original)
>> +++ llvm/trunk/lib/Fuzzer/FuzzerLoop.cpp Wed Dec  2 16:43:53 2015
>> @@ -238,7 +238,11 @@ void Fuzzer::RunOneAndUpdateCorpus(Unit
>>  }
>>
>>  void Fuzzer::ExecuteCallback(const Unit &U) {
>> -  int Res = USF.TargetFunction(U.data(), U.size());
>> +  const uint8_t *Data = U.data();
>> +  uint8_t EmptyData;
>> +  if (!Data)
>> +    Data = &EmptyData;
>> +  int Res = USF.TargetFunction(Data, U.size());
>>    (void)Res;
>>    assert(Res == 0);
>>  }
>>
>> Modified: llvm/trunk/lib/Fuzzer/test/SimpleTest.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Fuzzer/test/SimpleTest.cpp?rev=254558&r1=254557&r2=254558&view=diff
>>
>> ==============================================================================
>> --- llvm/trunk/lib/Fuzzer/test/SimpleTest.cpp (original)
>> +++ llvm/trunk/lib/Fuzzer/test/SimpleTest.cpp Wed Dec  2 16:43:53 2015
>> @@ -1,4 +1,5 @@
>>  // Simple test for a fuzzer. The fuzzer must find the string "Hi!".
>> +#include <assert.h>
>>  #include <cstdint>
>>  #include <cstdlib>
>>  #include <cstddef>
>> @@ -7,6 +8,7 @@
>>  static volatile int Sink;
>>
>>  extern "C" int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size) {
>> +  assert(Data);
>>    if (Size > 0 && Data[0] == 'H') {
>>      Sink = 1;
>>      if (Size > 1 && Data[1] == 'i') {
>>
>>
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>>
>
>
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