From: Florian Weimer <fweimer@redhat.com>
To: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Cc: "xuyang2018.jy@fujitsu.com" <xuyang2018.jy@fujitsu.com>,
Theodore Ts'o <tytso@mit.edu>,
"libc-alpha@sourceware.org" <libc-alpha@sourceware.org>,
"fstests@vger.kernel.org" <fstests@vger.kernel.org>
Subject: Re: [PATCH] src/ext4_resize.c: set errno to 0 before the strtoull call
Date: Tue, 18 Jan 2022 13:00:20 +0100 [thread overview]
Message-ID: <87h7a1jlt7.fsf@oldenburg.str.redhat.com> (raw)
In-Reply-To: <496a3521-5a0c-b3ae-29bb-02fd0056525b@linaro.org> (Adhemerval Zanella's message of "Tue, 18 Jan 2022 08:49:40 -0300")
* Adhemerval Zanella:
> On 18/01/2022 08:26, Florian Weimer wrote:
>> * Adhemerval Zanella:
>>
>>>
>>>
>>> On 18/01/2022 02:27, xuyang2018.jy--- via Libc-alpha wrote:
>>>> on 2022/1/18 11:56, Theodore Ts'o wrote:
>>>>> On Tue, Jan 18, 2022 at 02:43:26AM +0000, xuyang2018.jy@fujitsu.com wrote:
>>>>>>> You're right of course, but out of curiosity, which C library are you
>>>>>>> using?
>>>>>> I use glibc-2.34.
>>>>>
>>>>> Hmm, ok. I'm using glibc 2.31, and in this particular program, errno
>>>>> shouldn't have been set by any prior system call. I'm guessing maybe
>>>>> it was something in crt0 which ended up setting errno?
>>>> It maybe a glibc bug.
>>>> I cc glibc mailing list and see whether they have met this problem.
>>>>
>>>> @Florian
>>>>
>>>> Now, I use glibc-2.34 and run the following program[1] but the errno is
>>>> not 0 in the beginning. So is this a known bug on glibc-2.34(Theodore
>>>> doesn't meet this problem on glicb-2.31)?
>>>>
>>>> [1]https://git.kernel.org/pub/scm/fs/xfs/xfstests-dev.git/tree/src/ext4_resize.c
>>>
>>> The errno should be only set on a failure, no function shall set errno
>>> to 0 (it is a POSIX definition which glibc adheres). The application
>>> need to explicitly set errno to 0 before the function call to check if
>>> an error occurs.
>>
>> While this is true, I think errno should still be 0 at the start of the
>> program.
>
> I think this is a implementation detail, I am not aware that either C or
> POSIX now states it should initialized to any specific value (in fact,
> POSIX at Issue 5 [1] has removed the 'The value of errno is 0 at program
> start-up' on its description).
It would be nice to stay compatible with that.
> In any case, we set errno to be an uninitialized TLS variable. Unless we
> have a bug on .tbss initialization I think the issue is somewhere else.
I suspect it's some additional system call, which is why I requested
strace output.
Thanks,
Florian
next prev parent reply other threads:[~2022-01-18 12:00 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <1642405014-3287-1-git-send-email-xuyang2018.jy@fujitsu.com>
[not found] ` <YeYmzJG5M0y9BcMc@mit.edu>
[not found] ` <61E6298D.80006@fujitsu.com>
[not found] ` <YeY6Uh8I7RlsCicw@mit.edu>
2022-01-18 5:27 ` xuyang2018.jy
2022-01-18 11:23 ` Adhemerval Zanella
2022-01-18 11:26 ` Florian Weimer
2022-01-18 11:49 ` Adhemerval Zanella
2022-01-18 12:00 ` Florian Weimer [this message]
2022-01-18 12:04 ` Andreas Schwab
2022-01-18 12:26 ` Adhemerval Zanella
2022-01-18 14:02 ` Florian Weimer
2022-01-19 6:14 ` xuyang2018.jy
2022-01-19 7:19 ` xuyang2018.jy
2022-01-19 13:57 ` Cristian Rodríguez
2022-01-19 14:07 ` Cristian Rodríguez
2022-01-19 14:50 ` Andrew G. Morgan
2022-01-19 20:13 ` Theodore Ts'o
2022-01-18 14:22 ` Andreas Schwab
2022-01-18 14:29 ` H.J. Lu
2022-01-18 14:43 ` Yann Droneaud
2022-01-18 14:54 ` H.J. Lu
2022-01-18 15:30 ` Andreas Schwab
2022-01-19 2:07 ` xuyang2018.jy
2022-01-19 8:23 ` Andreas Schwab
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=87h7a1jlt7.fsf@oldenburg.str.redhat.com \
--to=fweimer@redhat.com \
--cc=adhemerval.zanella@linaro.org \
--cc=fstests@vger.kernel.org \
--cc=libc-alpha@sourceware.org \
--cc=tytso@mit.edu \
--cc=xuyang2018.jy@fujitsu.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).