[Bug 56837] New: Bad file pointer after a file write in appending mode

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WineHQ Bugzilla

14 Jun 2024 14 Jun '24

8:22 p.m.

https://bugs.winehq.org/show_bug.cgi?id=56837

Bug ID: 56837 Summary: Bad file pointer after a file write in appending mode Product: Wine Version: unspecified Hardware: x86-64 OS: Linux Status: UNCONFIRMED Severity: normal Priority: P2 Component: -unknown Assignee: wine-bugs@winehq.org Reporter: sldev@free.fr Distribution: Other

Created attachment 76648 --> https://bugs.winehq.org/attachment.cgi?id=76648 bug-demo program and its source file

When writing for append into a file, Wine returns a bad ftell() file pointer unless a fflush() is performed before querying with ftell().

See the bug-demo program (run it under bare metal Windows, then under Wine).

This bug has existed like forever (Wine 6 and newer, for sure).

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WineHQ Bugzilla

17 Jun 17 Jun

11:54 p.m.

New subject: [Bug 56837] Bad file pointer after a file write in appending mode

https://bugs.winehq.org/show_bug.cgi?id=56837

Fabian Maurer dark.shadow4@web.de changed:

What |Removed |Added ---------------------------------------------------------------------------- CC| |dark.shadow4@web.de

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WineHQ Bugzilla

22 Mar 22 Mar

1:53 p.m.

New subject: [Bug 56837] Bad file pointer after a file write in appending mode

https://bugs.winehq.org/show_bug.cgi?id=56837

reserv0@yahoo.com changed:

What |Removed |Added ---------------------------------------------------------------------------- CC| |reserv0@yahoo.com

--- Comment #1 from reserv0@yahoo.com --- *BUMP*

Is anyone looking into this?

This bug causes cache files corruptions with some applications and is pretty serious, since it breaks a very basic underlying standard C library call.

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WineHQ Bugzilla

9:42 p.m.

New subject: [Bug 56837] Bad file pointer after a file write in appending mode

https://bugs.winehq.org/show_bug.cgi?id=56837

Austin English austinenglish@gmail.com changed:

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WineHQ Bugzilla

23 Mar 23 Mar

9:43 a.m.

New subject: [Bug 56837] Bad file pointer after a file write in appending mode

https://bugs.winehq.org/show_bug.cgi?id=56837

--- Comment #2 from Dmitry Timoshkov dmitry@baikal.ru --- Created attachment 78272 --> https://bugs.winehq.org/attachment.cgi?id=78272 patch

This patch makes the attached test work in Wine.

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WineHQ Bugzilla

9:44 a.m.

New subject: [Bug 56837] Bad file pointer after a file write in appending mode

https://bugs.winehq.org/show_bug.cgi?id=56837

Dmitry Timoshkov dmitry@baikal.ru changed:

What |Removed |Added ---------------------------------------------------------------------------- CC| |piotr.caban@gmail.com

--- Comment #3 from Dmitry Timoshkov dmitry@baikal.ru --- Adding Piotr, probably he has an opinion on this.

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WineHQ Bugzilla

9:46 a.m.

New subject: [Bug 56837] Bad file pointer after a file write in appending mode

https://bugs.winehq.org/show_bug.cgi?id=56837

--- Comment #4 from Dmitry Timoshkov dmitry@baikal.ru --- Created attachment 78273 --> https://bugs.winehq.org/attachment.cgi?id=78273 Modified test with more traces

Modified test adds traces to compare FILE and fd backend behaviour.

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WineHQ Bugzilla

9:47 a.m.

New subject: [Bug 56837] Bad file pointer after a file write in appending mode

https://bugs.winehq.org/show_bug.cgi?id=56837

Dmitry Timoshkov dmitry@baikal.ru changed:

--- Comment #5 from Dmitry Timoshkov dmitry@baikal.ru --- Confirming.

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WineHQ Bugzilla

9:48 a.m.

New subject: [Bug 56837] Bad file pointer after a file write in appending mode

https://bugs.winehq.org/show_bug.cgi?id=56837

Dmitry Timoshkov dmitry@baikal.ru changed:

--- Comment #6 from Dmitry Timoshkov dmitry@baikal.ru --- Created attachment 78274 --> https://bugs.winehq.org/attachment.cgi?id=78274 patch

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WineHQ Bugzilla

24 Mar 24 Mar

8:55 a.m.

New subject: [Bug 56837] Bad file pointer after a file write in appending mode

https://bugs.winehq.org/show_bug.cgi?id=56837

--- Comment #7 from sldev sldev@free.fr --- Yup, the proposed patch does fix the issue, thank you ! :-)

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WineHQ Bugzilla

10:23 a.m.

New subject: [Bug 56837] Bad file pointer after a file write in appending mode

https://bugs.winehq.org/show_bug.cgi?id=56837

Piotr Caban piotr.caban@gmail.com changed:

What |Removed |Added ---------------------------------------------------------------------------- Component|-unknown |msvcrt

--- Comment #8 from Piotr Caban piotr.caban@gmail.com --- I have created MR that should fix the bug: https://gitlab.winehq.org/wine/wine/-/merge_requests/7651

It's based on Dmitry's patch but moves seek to _flsbuf function.

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WineHQ Bugzilla

3:33 p.m.

New subject: [Bug 56837] Bad file pointer after a file write in appending mode

https://bugs.winehq.org/show_bug.cgi?id=56837

--- Comment #9 from sldev sldev@free.fr --- (In reply to Piotr Caban from comment #8)

...

I have created MR that should fix the bug: https://gitlab.winehq.org/wine/wine/-/merge_requests/7651

It's based on Dmitry's patch but moves seek to _flsbuf function.

Err, no, this is not a correct fix for the issue at hand. The problem was that the write happened at the start of the file instead of at the end, while the file was opened in append mode (with no lseek() call used at all: see the bug-demo sources).

The suggested patch ( https://bugs.winehq.org/attachment.cgi?id=78274 ) is exactly what we need and what restores the normal behaviour of fwrite() in append mode.

Instead, https://gitlab.winehq.org/wine/wine/-/merge_requests/7651 addresses only an issue with _lseek(), which won't fix our issue.

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WineHQ Bugzilla

3:38 p.m.

New subject: [Bug 56837] Bad file pointer after a file write in appending mode

https://bugs.winehq.org/show_bug.cgi?id=56837

--- Comment #10 from Piotr Caban piotr.caban@gmail.com --- I don't understand what's wrong, could you please describe it in more detail? I have verified that both test application output and file content is the same as on Windows.

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WineHQ Bugzilla

3:45 p.m.

New subject: [Bug 56837] Bad file pointer after a file write in appending mode

https://bugs.winehq.org/show_bug.cgi?id=56837

--- Comment #11 from Dmitry Timoshkov dmitry@baikal.ru --- (In reply to Piotr Caban from comment #10)

...

I don't understand what's wrong, could you please describe it in more detail? I have verified that both test application output and file content is the same as on Windows.

I can confirm that with the proposed MR 7651 attached test shows same result under Wine as observed under Windows.

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WineHQ Bugzilla

5:36 p.m.

New subject: [Bug 56837] Bad file pointer after a file write in appending mode

https://bugs.winehq.org/show_bug.cgi?id=56837

--- Comment #12 from sldev sldev@free.fr --- (In reply to Piotr Caban from comment #10)

...

I don't understand what's wrong, could you please describe it in more detail? I have verified that both test application output and file content is the same as on Windows.

(In reply to Dmitry Timoshkov from comment #11)

...

(In reply to Piotr Caban from comment #10)

...
I don't understand what's wrong, could you please describe it in more detail? I have verified that both test application output and file content is the same as on Windows.

I can confirm that with the proposed MR 7651 attached test shows same result under Wine as observed under Windows.

Hmm... Maybe, *if* _flsbuf() is *systematically* called during fwrite() ?... I must admit I did not look at the surrounding code and I'm not familiar with Wine at a source code level... But the first patch looked "safer" to me, since the file pointer was set just before the actual write to the file.

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WineHQ Bugzilla

5:47 p.m.

New subject: [Bug 56837] Bad file pointer after a file write in appending mode

https://bugs.winehq.org/show_bug.cgi?id=56837

--- Comment #13 from Piotr Caban piotr.caban@gmail.com --- The actual write to the file happens in _write function (not in fwrite). _write calls _lseek before writing to the file. So we're only trying to fix value returned by ftell/tell. The position where data is written to the file is not changed by any of these patches.

It's possible to find where seek is happening. I have written some tests to confirm it should not happen in every call to fwrite. I didn't add them to the patch because I don't think it shows anything useful - I have added flsbuf() tests instead.

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WineHQ Bugzilla

25 Mar 25 Mar

9:02 a.m.

New subject: [Bug 56837] Bad file pointer after a file write in appending mode

https://bugs.winehq.org/show_bug.cgi?id=56837

Dmitry Timoshkov dmitry@baikal.ru changed:

--- Comment #14 from Dmitry Timoshkov dmitry@baikal.ru --- This should be fixed by a165fd43dc4c115d9e9ca0cc81739045ea5f5fe5.

If the problem persists please feel free to reopen.

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WineHQ Bugzilla

9:36 a.m.

New subject: [Bug 56837] Bad file pointer after a file write in appending mode

https://bugs.winehq.org/show_bug.cgi?id=56837

--- Comment #15 from sldev sldev@free.fr --- I just made a build (of Wine 10.2, because 10.3+ makes CEF crash, and I need the latter) with a165fd43dc4c115d9e9ca0cc81739045ea5f5fe5 applied, and I can confirm that this issue is fixed for the program I was seeing it happening with (and for the bug-demo program).

Thank you ! :-)

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