Re: [PATCH] tag: avoid NULL pointer arithmetic

> On Sun, Oct 01, 2017 at 04:45:13PM +0200, René Scharfe wrote:
> 
>> lookup_blob() etc. can return NULL if the referenced object isn't of the
>> expected type.  In theory it's wrong to reference the object member in
>> that case.  In practice it's OK because it's located at offset 0 for all
>> types, so the pointer arithmetic (NULL + 0) is optimized out by the
>> compiler.  The issue is reported by Clang's AddressSanitizer, though.
>>
>> Avoid the ASan error by casting the results of the lookup functions to
>> struct object pointers.  That works fine with NULL pointers as well.  We
>> already rely on the object member being first in all object types in
>> other places in the code.
> 
> Out of curiosity, did you have to do anything to coax this out of ASan
> (e.g., a specific version)?  I've been running it pretty regularly and
> didn't see this one (I did switch from clang to gcc a month or two ago,
> but this code is pretty old, I think).