Re: [PATCH, ARM] Don't use __thumb2__ to select _REENT_SMALL

[Jeff Johnston <jjohnstn at redhat dot com>]

Paul Brook wrote:
> On Tuesday 02 June 2009, Paul Brook wrote:
>   
> > > Yes, this leaks out into user code -- at least it does for me.  Try
> > > building the standard arm-eabi multilib tools and then running the gcc
> > > testsuite with -mcpu=cortex-a8 and -mthumb.  Programs such as
> > > gcc.c-torture/exectute/fprintf-1.c will then fail.
> > >
> > > The definition of stdout is:
> > > #define stdout  (_REENT->_stdout)
> > >       
> > In my sources this field lives at the same location in both cases.
> >     
>
> Further investigation indicates upstream newlib is missing the following 
> patch.
>
> 2009-06-02  Paul Brook  <paul@codesourcery.com>
>
> 	newlib/
> 	* libc/include/sys/reent.h (_reent): Adjust _REENT_SMALL to be binary
> 	compatible with normal layout
>
>   
This would require changing the initialization macro in kind or else 
there will be trouble.  I'm not thrilled with leaving two gaps in the 
struct for 16-bit platforms, but there are now 2 unused fields since 
Corinna revamped locale support.  If the unpaired int that is caused by 
the errno move was put below and the unused fields were removed, I could 
certainly live with that as the struct gets smaller and there is one 
left-over int anyway.  Might as well be errno.

That said, I agree with Richard's point.  If the thumb2 flag is not a 
proper check for a platform that requires a small reent struct, then it 
shouldn't be used as such.

Perhaps a staggered approach can be used.  Make the reent change now as 
a stop-gap and work on changing the compiler so that a proper check can 
be made for when reent small should really be used and a proper multilib 
is created.  For now, put a comment in that the thumb2 check is wrong 
and needs to be changed.

Seem reasonable?

-- Jeff J.
> Index: newlib/libc/include/sys/reent.h
> ===================================================================
> --- newlib/libc/include/sys/reent.h	(revision 159552)
> +++ newlib/libc/include/sys/reent.h	(revision 159553)
> @@ -344,14 +344,15 @@ struct _misc_reent
>   * ports with 16-bit int's but 32-bit pointers, align nicely.  */
>  struct _reent
>  {
> +  /* As an exception to the above put _errno first for binary
> +     compatibility with non _REENT_SMALL targets.  */
> +  int _errno;			/* local copy of errno */
>  
>    /* FILE is a big struct and may change over time.  To try to achieve binary
>       compatibility with future versions, put stdin,stdout,stderr here.
>       These are pointers into member __sf defined below.  */
>    __FILE *_stdin, *_stdout, *_stderr;	/* XXX */
>  
> -  int _errno;			/* local copy of errno */
> -
>    int  _inc;			/* used by tmpnam */
>  
>    char *_emergency;
>
>