Re: impure_data never reclaimed (unless you add the required cleanup code)

[Fabian Vogt <fabian@ritter-vogt.de>]

Hi,

Am Samstag, 5. Dezember 2020, 16:48:57 CET schrieb Dave Nadler:
> Hi Fabian - Yes, that is correct, you need that cleanup code.
> However, you must also allocate (and clean up) the reentrancy structure 
> for each task/thread.
> FreeRTOS correctly does this on task/thread creation and cleanup (with 
> #define configUSE_NEWLIB_REENTRANT  1).
> Hope that helps!

While searching for more info about this I found your related thread on this ML
from some time ago, but I think it's not the same situation.

newlib/libc/reent/impure.c has:
static struct _reent __ATTRIBUTE_IMPURE_DATA__ impure_data = _REENT_INIT (impure_data);
struct _reent *__ATTRIBUTE_IMPURE_PTR__ _impure_ptr = &impure_data;

So the struct for the main (without thread support, the only) thread is
allocated statically by newlib.

It would be possible to do it like FreeRTOS and just allocate a new struct for
_impure_ptr for the main thread, but that would leave impure_data unused and
thus waste space and need more code on top.

Cheers,
Fabian

> Best Regards, ,Dave
> 
> On 12/5/2020 9:27 AM, Fabian Vogt wrote:
> > Hi,
> >
> > I'm using newlib as libc on top of an OS which provides malloc and free.
> > Threads aren't supported, but programs can be started and stopped. The used
> > heap is shared between all programs, so leaked memory is lost forever. Thus
> > it is important that after a clean exit, every allocation was properly freed.
> >
> > Currently this simple program leaks three allocations though:
> >
> > #include <stdio.h>
> > int main()
> > {
> >      setbuf(stdout, NULL); // This would be properly freed, avoid distraction
> >      printf("This is 0.5 as a float: %f\n", 0.5f);
> > }
> >
> > Those are from Balloc, which allocates a list also for later use.
> > FWICT, _reclaim_reent takes care of freeing the list and its contents, but:
> > - _reclaim_reent is never called for _impure_ptr (== &impure_data)
> > - _reclaim_reent does nothing if impure_ptr is passed
> >
> > Is the OS glue code supposed to do something like this in _exit?
> >
> >      struct _reent *global_reent = _impure_ptr;
> >      _impure_ptr = NULL;
> >      _reclaim_reent(global_reent);
> >
> > With that the leaks are gone, but it seems a bit odd to me.
> >
> > Thanks,
> > Fabian