From: Kaz Kylheku <920-082-4242@kylheku.com>
To: cygwin@cygwin.com
Subject: Re: Problem with line buffering and getc function on 1.7.33.
Date: Sun, 13 Mar 2016 00:37:00 -0000 [thread overview]
Message-ID: <ebae78105462dee607c99bc191f797fc@mail.kylheku.com> (raw)
In-Reply-To: <20160312222921.GD3567@calimero.vinschen.de>
On 12.03.2016 14:29, Corinna Vinschen wrote:
> On Mar 12 20:39, Corinna Vinschen wrote:
>> On Mar 11 16:05, Kaz Kylheku wrote:
>> > We can reproduce the problem with just file streams using
>> > a much simpler program:
>> >
>> > #include <stdio.h>
>> >
>> > int main(void)
>> > {
>> > FILE *out = fopen("file", "w+");
>> > setvbuf(out, (char *) NULL, _IOLBF, 0);
>> > getc(out);
>> > clearerr(out);
>> > fseek(out, 0, SEEK_SET);
>> > putc('a', out);
>> > putc('b', out);
>> > putc('c', out);
>> > putc('d', out);
>> > putc('e', out);
>> > putc('\n', out);
>> > fclose(out);
>> > return 0;
>> > }
>> >
>> > The contents of file end up being "\n": one empty
>> > line, instead of "abcde\n":
>> >
>> > $ cat file
>> >
>> > $
>>
>> Thanks for the testcase. I can reproduce the issue and I see where
>> the
>> problem occurs, but I'm still puzzled. Comparing the code in our
>> newlib
>> C library with its BSD counterparts, I could swear the same behaviour
>> happens on OpenBSD as well. If not (which needs testing), I wonder
>> why
>> and where newlib's actually different. Right now I don't see the
>> difference.
>
> I do now. Basically it's setvbuf screwing up the internal flags in the
> FILE structure. I took the liberty to update newlib's setvbuf to the
> OpenBSD version locally and I'm going to apply my patches to newlib
> soon. I'll provide a new 2.5.0 test release of Cygwin with this patch
> tomorrow or early next week.
Indeed, I thought it would have something to do with the
stream->_flags, because when I single-stepped over the getc(stream)
line (necessary for the problem to repro, IIRC) the only apparent state
change in the stream was to the _flags member:
(gdb) n
8 getc(out);
(gdb) p *out
$2 = {_p = 0x80039c28 "", _r = 0, _w = 0, _flags = -30575, _file = 3,
_bf = {
^^^^^^^^^^^^^^^^
_base = 0x80039c28 "", _size = 1024}, _lbfsize = -1024, _data = 0x0,
_cookie = 0x80039a30, _read = 0x61164cb0 <__sread>,
_write = 0x61164f30 <__swrite64>, _seek = 0x61164e50 <__sseek>,
_close = 0x61164ea0 <__sclose>, _ub = {_base = 0x0, _size = 0}, _up =
0x0,
_ur = 0, _ubuf = "\000\000", _nbuf = "", _lb = {_base = 0x0, _size =
0},
_blksize = 0, _flags2 = 0, _offset = 0, _seek64 = 0x61164ed0
<__sseek64>,
_lock = 0x80039bf8, _mbstate = {__count = 0, __value = {__wch = 0,
__wchb = "\000\000\000"}}}
(gdb) n
9 clearerr(out);
(gdb) p *out
$3 = {_p = 0x80039c28 "", _r = 0, _w = 0, _flags = -22347, _file = 3,
_bf = {
^^^^^^^^^^^^^^^^^^
_base = 0x80039c28 "", _size = 1024}, _lbfsize = -1024, _data = 0x0,
_cookie = 0x80039a30, _read = 0x61164cb0 <__sread>,
_write = 0x61164f30 <__swrite64>, _seek = 0x61164e50 <__sseek>,
_close = 0x61164ea0 <__sclose>, _ub = {_base = 0x0, _size = 0}, _up =
0x0,
_ur = 0, _ubuf = "\000\000", _nbuf = "", _lb = {_base = 0x0, _size =
0},
_blksize = 0, _flags2 = 0, _offset = 0, _seek64 = 0x61164ed0
<__sseek64>,
_lock = 0x80039bf8, _mbstate = {__count = 0, __value = {__wch = 0,
__wchb = "\000\000\000"}}}
--
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next prev parent reply other threads:[~2016-03-13 0:37 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-03-11 21:57 Kaz Kylheku
2016-03-11 22:14 ` Marco Atzeri
2016-03-12 0:05 ` Kaz Kylheku
2016-03-12 19:39 ` Corinna Vinschen
2016-03-12 22:29 ` Corinna Vinschen
2016-03-13 0:37 ` Kaz Kylheku [this message]
2016-03-13 10:47 ` Corinna Vinschen
2016-03-13 0:41 ` Kaz Kylheku
2016-03-13 11:06 ` Corinna Vinschen
2016-03-13 11:37 ` Corinna Vinschen
-- strict thread matches above, loose matches on Subject: below --
2016-03-11 19:17 Kaz Kylheku
2016-03-11 20:09 ` Yaakov Selkowitz
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