basic question about using configUSE_NEWLIB_REENTRANT 1

sagi2097 wrote on Thursday, March 13, 2014:

Hello I have a question regarding the use of configUSE_NEWLIB_REENTRANT. Let me tell you first, that I have not used it before, so I am not familiar with all the details. All I understand is that it embedds a struct compatible with reent.h in the TCB so one does not have to allocate and point to that struct manually. Correct me if I am wrong here…
Now the question: Suppose a simple case where I would like to use reentrancy features, so i set configUSE_NEWLIB_REENTRANT to 1. In a task lets say that all I do is use sprintf in the reentrant version :_sprintf_r. This version demands as second argument a pointer to the reent struct. what is the correct way to use this version of sprintf in this case? dig out the reent pointer from TCB and pass it by hand? Something like _sprintf_r(buff,pxTCB->xNewLib_reent,"…"); ??
Maybe what I write irrelevant … but I could use an example to get started.
Thank You


rtel wrote on Thursday, March 13, 2014:

As far as I know, if you are using newlib, then you should be able to just use the normal library functions and the kernel takes care of ensuring the reent structure is set correctly for whichever task is running at that time. I’m not familiar with functions that end in _r, but if they are asking you to use the reent structure manually then you should be able to pass _impure_ptr, which will be pointing to the correct reent structure - don’t try obtaining it from the TCB as that would require code changes. Try googling _impure_ptr.

I suspect the functions you are using are not intended to be called directly, but indirectly from the standard library functions, but as noted in the comments where the reent manipulation is implemented in the code, I don’t use this functionality myself so can give a very authoritative answer without checking google myself.