Re: Use of valgrind with microthreading

Hi Shachar,

On Fri, Aug 14, 2020 at 06:35:14PM +0300, Shachar Shemesh wrote:
> I am writing my own C++ microthreading library. At the very first switch, I
> get the following message from Valgrind:
> 
> ==15122== Warning: client switching stacks?  SP change: 0x1ffeffe788 -->
> 0x75d0f80
> ==15122==          to suppress, use: --max-stackframe=137298630664 or
> greater
> 
> 
> I understand that valgrind needs to know where the stack starts and ends. I
> am wondering whether is any way I can tell it that information. Since I'm
> writing the library, what I was thinking was compiling the library with a
> special flag saying "you're running with valgrind", and then have my library
> call a valgrind function that says "This is the new stack range, this is the
> old one".
>  
> Is there such a thing? If so, how do I interface with it?

Yes, there is such a thing. The valgrind client request mechanism:
https://valgrind.org/docs/manual/manual-core-adv.html#manual-core-adv.clientreq

It does have various VALGRIND_STACK_* macros to signal use of user
threads/stacks. But note that the documentations says:
Warning: Unfortunately, this client request is unreliable and best avoided.
Unfortunately I don't know why that is, or what alternative mechanisms there are.

Cheers,

Mark