* Broken getchar() and putchar() macros?
@ 2017-08-02 11:36 Sebastian Huber
2017-08-02 12:37 ` Corinna Vinschen
0 siblings, 1 reply; 2+ messages in thread
From: Sebastian Huber @ 2017-08-02 11:36 UTC (permalink / raw)
To: Newlib
Hello,
we have via <stdio.h>
#define getchar() getc(stdin)
#define putchar(x) putc(x, stdout)
which is
#ifndef __CYGWIN__
#ifndef lint
#define getc(fp) __sgetc_r(_REENT, fp)
#define putc(x, fp) __sputc_r(_REENT, x, fp)
#endif /* lint */
#endif /* __CYGWIN__ */
#endif /* __cplusplus */
which is mostly
#define __sgetc_r(__ptr, __p) __sgetc_raw_r(__ptr, __p)
#define __sputc_r(__ptr, __c, __p) __sputc_raw_r(__ptr, __c, __p)
which is
/*
* The __sfoo macros are here so that we can
* define function versions in the C library.
*/
#define __sgetc_raw_r(__ptr, __f) (--(__f)->_r < 0 ?
__srget_r(__ptr, __f) : (int)(*(__f)->_p++))
_ELIDABLE_INLINE int __sputc_r(struct _reent *_ptr, int _c, FILE *_p) {
#ifdef __SCLE
if ((_p->_flags & __SCLE) && _c == '\n')
__sputc_r (_ptr, '\r', _p);
#endif
if (--_p->_w >= 0 || (_p->_w >= _p->_lbfsize && (char)_c != '\n'))
return (*_p->_p++ = _c);
else
return (__swbuf_r(_ptr, _c, _p));
}
which modifies FILE members without protection of the FILE lock!
We also have via <stdio.h>:
int _EXFUN(getchar, (void));
int _EXFUN(putchar, (int));
Which are defined in using #undef putchar and #undef getchar:
libc/stdio/putchar.c
libc/stdio/getchar.c
These function use the FILE lock eventually.
What is the purpose of these macros? We had some crashes, due to an
invalid FILE::_w value during concurrent output to stdout.
--
Sebastian Huber, embedded brains GmbH
Address : Dornierstr. 4, D-82178 Puchheim, Germany
Phone : +49 89 189 47 41-16
Fax : +49 89 189 47 41-09
E-Mail : sebastian.huber@embedded-brains.de
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Diese Nachricht ist keine geschäftliche Mitteilung im Sinne des EHUG.
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: Broken getchar() and putchar() macros?
2017-08-02 11:36 Broken getchar() and putchar() macros? Sebastian Huber
@ 2017-08-02 12:37 ` Corinna Vinschen
0 siblings, 0 replies; 2+ messages in thread
From: Corinna Vinschen @ 2017-08-02 12:37 UTC (permalink / raw)
To: newlib
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On Aug 2 13:36, Sebastian Huber wrote:
> Hello,
>
> we have via <stdio.h>
>
> #define getchar() getc(stdin)
> #define putchar(x) putc(x, stdout)
>
> which is
>
> #ifndef __CYGWIN__
> #ifndef lint
> #define getc(fp) __sgetc_r(_REENT, fp)
> #define putc(x, fp) __sputc_r(_REENT, x, fp)
> #endif /* lint */
> #endif /* __CYGWIN__ */
> #endif /* __cplusplus */
>
> which is mostly
>
> #define __sgetc_r(__ptr, __p) __sgetc_raw_r(__ptr, __p)
>
> #define __sputc_r(__ptr, __c, __p) __sputc_raw_r(__ptr, __c, __p)
>
> which is
>
> /*
> * The __sfoo macros are here so that we can
> * define function versions in the C library.
> */
> #define __sgetc_raw_r(__ptr, __f) (--(__f)->_r < 0 ? __srget_r(__ptr,
> __f) : (int)(*(__f)->_p++))
>
> _ELIDABLE_INLINE int __sputc_r(struct _reent *_ptr, int _c, FILE *_p) {
> #ifdef __SCLE
> if ((_p->_flags & __SCLE) && _c == '\n')
> __sputc_r (_ptr, '\r', _p);
> #endif
> if (--_p->_w >= 0 || (_p->_w >= _p->_lbfsize && (char)_c != '\n'))
> return (*_p->_p++ = _c);
> else
> return (__swbuf_r(_ptr, _c, _p));
> }
>
> which modifies FILE members without protection of the FILE lock!
> [...]
> What is the purpose of these macros?
If you search for them in newlib, you'll notice that the macros are used
from a couple of places in libc/stdio.
The fact that they are directly called on non-Cygwin platforms is probably
historical, as usual. They are reentrant. As such, and under the
assumption that we're on embedded platforms without preemptive
multi-tasking, the macros work nicely and are faster than the function
calls.
I can think of four ways to solve this:
1. Just add RTEMS to the exceptions, same as Cygwin.
2. Replace
#define getc(fp) __sgetc_r(_REENT, fp)
#define putc(x, fp) __sputc_r(_REENT, x, fp)
with
#define getc_unlocked(fp) __sgetc_r(_REENT, fp)
#define putc_unlocked(x, fp) __sputc_r(_REENT, x, fp)
and let getc/putc simply call the functions.
3. Add a newlib setting to sys/config.h and use that in stdio.h, rather
than excluding targets explicitely. Best is probably an opt-in
config.
4. Move the macros to libc/stdio/local.h and don't use them from
user space at all. This may be a bit harsh on some embedded
targets, but actually I don't know. Most targets have space
constraints and a function would be more prudent then, I guess.
Corinna
--
Corinna Vinschen
Cygwin Maintainer
Red Hat
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