Broken getchar() and putchar() macros?

Sebastian Huber sebastian.huber@embedded-brains.de
Wed Aug 2 11:36:00 GMT 2017


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
PGP     : Public key available on request.

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