Re: [Valgrind-users] about memory error

[Xiaopi <liu...@gm...>]

Thank you for the reply.
Looks like there is API for this, after google with your suggestion.
But I still don't quite understand.
Are u meaning that if we write more bytes than the malloc usable size, it is corrupted for the ptr?

Thanks,



2013-7-16，18:32，vijay nag <vi...@gm...> 

> On Tue, Jul 16, 2013 at 3:53 PM, Xiaopi Liu <liu...@gm...> wrote:
>> Dear all,
>> 
>> 
>> I have see this error/crash in an existing large code base.
>> Just cannot identify the exact crash point, even using valgrind.
>> Can someone help point out what exactly this crash/error means?
>> 
>> Does it necessarily related to malloc/free operation?
>> By this I mean,  if only new/delete op is used, will I still see the same
>> error?
>> Any general background on the possible cause for this?
>> 
>> 
>> *** glibc detected *** .: free(): invalid next size (fast)
>> 
>> --
>> 
>> 
>> Best wishes!
>> Sincerely yours, LIU
>> 
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> It could either be corruption or double free error. Mostly the
> malloc_usable_size is corrupted here.
> You can get the malloc_usable_size the following way.
> 
> malloc_usable_size(ptr)
> {
>   char * p = (char*)ptr;
>   size = *(p -4);
>    if (size & 2) {
>      blockSize =  (size & ~3) - 2*4;
>    } else {
>       blockSize = (size & ~3) -4;
>   }
> }