Re: [PATCH] Delete default __getreent() implementation

[Corinna Vinschen <vinschen at redhat dot com>]

On Nov  7 11:12, Craig Howland wrote:
> On 11/07/2017 10:03 AM, Corinna Vinschen wrote:
> > On Nov  7 12:53, Sebastian Huber wrote:
> > > Systems defining  __DYNAMIC_REENT__ have to provide a proper
> > > implementation of __getreent().  Do not include a default implementation
> > > to avoid a potential link time issue (real vs. default implementation of
> > > __getreent()).
> > Ok, please push (without the kill_r removal).
> > 
> > 
> > Thanks,
> > Corinna
> > 
> Hold on a minute!  This patch is making assumptions that are not necessarily
> true, and will break backwards compatibility.  Quoting from reent.h:
> 
>  "Dynamic reentrancy is specified by the __DYNAMIC_REENT__ flag. This
>    flag denotes setting up a macro to replace _REENT with a function call
>    to __getreent().  This function needs to be implemented by the platform
>    and it is meant to return the reentrancy structure for the current
>    thread."
> 
> While this text has an implied expectation that the platform is intended to
> supply the function, this implication is not true because there is a default
> implementation--one that really does work.  And given it is there by
> default, people have likely just used it.  In fact, I have an implementation
> from 10 years ago that does use the default implementation.  (The task
> switch is very simple, just re-assigning the value of impure_ptr.)  While I
> do not presently have plans to change from the old Newlib used in that
> project, it is an obvious example of breakage if I were to need to update
> that application to a Newlib version in which this change had been made.  It
> is easy to envision that others have done the same thing.
> 
> I suggest that at a minimum the contents of getreent.c should be kept.  This
> keeps a starting point for people who are needing to supply such a
> function.  (Leaving it out of the library stops the link problem which is
> the stated goal of the patch.)  But I think it needs to go further, and this
> patch should not be done in this form because of the cited
> backwards-compatibility reasons.  If something were to be done it should be
> a configure flag to leave it out of the library.
> 
> Craig

Good point.


Corinna

-- 
Corinna Vinschen
Cygwin Maintainer
Red Hat

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