[src/trunk]: src/lib/libc/stdio restore change from rev 1.23 "Avoid undefined...

[jdolecek <jdolecek%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/1d5733311823
branches:  trunk
changeset: 959302:1d5733311823
user:      jdolecek <jdolecek%NetBSD.org@localhost>
date:      Sun Feb 07 15:54:09 2021 +0000

description:
restore change from rev 1.23 "Avoid undefined behavior in fread(3)", mistakely
removed as part __SNBF optimization

diffstat:

 lib/libc/stdio/fread.c |  12 ++++++++----
 1 files changed, 8 insertions(+), 4 deletions(-)

diffs (46 lines):

diff -r 9a0cae0526d4 -r 1d5733311823 lib/libc/stdio/fread.c
--- a/lib/libc/stdio/fread.c    Sun Feb 07 15:51:11 2021 +0000
+++ b/lib/libc/stdio/fread.c    Sun Feb 07 15:54:09 2021 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: fread.c,v 1.25 2021/02/01 17:50:53 jdolecek Exp $      */
+/*     $NetBSD: fread.c,v 1.26 2021/02/07 15:54:09 jdolecek Exp $      */
 
 /*-
  * Copyright (c) 1990, 1993
@@ -37,7 +37,7 @@
 #if 0
 static char sccsid[] = "@(#)fread.c    8.2 (Berkeley) 12/11/93";
 #else
-__RCSID("$NetBSD: fread.c,v 1.25 2021/02/01 17:50:53 jdolecek Exp $");
+__RCSID("$NetBSD: fread.c,v 1.26 2021/02/07 15:54:09 jdolecek Exp $");
 #endif
 #endif /* LIBC_SCCS and not lint */
 
@@ -81,8 +81,6 @@
        _DIAGASSERT(buf != NULL);
 
        FLOCKFILE(fp);
-       if (fp->_r < 0)
-               fp->_r = 0;
        total = resid;
        p = buf;
 
@@ -115,12 +113,18 @@
                return (count);
        }
 
+       if (fp->_r <= 0) {
+               /* Nothing to read on enter, refill the buffers. */
+               goto refill;
+       }
+
        while (resid > (size_t)(r = fp->_r)) {
                (void)memcpy(p, fp->_p, (size_t)r);
                fp->_p += r;
                /* fp->_r = 0 ... done in __srefill */
                p += r;
                resid -= r;
+refill:
                if (__srefill(fp)) {
                        /* no more input: return partial result */
                        FUNLOCKFILE(fp);