Re: [Valgrind-users] Invalid read well inside a block alloc'd

[Paul-Antoine A. <li...@de...>]

Le 14/01/2020 à 20:01, Tom Hughes a écrit :
> On 14/01/2020 18:55, Paul-Antoine Arras wrote:
>> Le 14/01/2020 à 19:51, Tom Hughes a écrit :
>>> On 14/01/2020 16:53, Paul-Antoine Arras wrote:
>>>
>> [...]
>>>> I struggle to understand how a read into a block of properly alloc'd 
>>>> memory can be invalid, given that the application doesn't use client 
>>>> requests.
>> [...]
>>>> How can a block of dynamically-allocated memory be marked 
>>>> unaddressable without having been freed?
>>>
>>> By using the VALGRIND_MAKE_MEM_NOACCESS macro.
>>>
>>
>> Sure, but as I mentioned in my message, the application code does not 
>> use client requests.
> 
> Using it as a thread stack could also do it, though it looks a
> bit small for that, or some sort or whacky stack pointer stunts
> that lead to valgrind thinking it's part of the stack.
> 

That's interesting. The block in question is not a thread stack but a 
regular struct. However, at other places the code does play with 
manually-allocated thread stacks, hence stack pointer switches that 
might confuse Valgrind.

Can you see a way to confirm this conjecture? In other words, how can I 
ensure this is a legitimate false positive?

Many thanks,
-- 
Paul-Antoine Arras