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Date: Tue, 19 Jun 2012 22:10:11 -0600
From: Eric Blake <>
To: Rich Felker <>
CC:, Isaac Dunham <>,
        Paul Eggert <>,,
        Reuben Thomas <>
Subject: Re: Re: musl bugs found through gnulib

On 06/19/2012 09:04 PM, Rich Felker wrote:

>> Replacement of duplocale, because of
>>   checking whether duplocale(LC_GLOBAL_LOCALE) works... no
> POSIX does not specify any use of LC_GLOBAL_LOCALE except as an
> argument to uselocale. Is there a reason it's needed? Perhaps more
> importantly, is the replacement when libc doesn't provide this
> functionality bloated/painful?

Unfortunately, you are out of date.  POSIX _does_ require
duplocale(LC_GLOBAL_LOCALE) to work:

    If the locobj argument is LC_GLOBAL_LOCALE, duplocale() shall
    create a new locale object containing a copy of the global locale
    determined by the setlocale() function.

    The behavior is undefined if the locobj argument is not a valid
    locale object handle.

  After line 24978 add a new paragraph to APPLICATION USAGE:

    The duplocale() function can also be used in conjunction with
    uselocale((locale_t)0). This returns the locale in effect for
    the calling thread, but can have the value LC_GLOBAL_LOCALE.
    Passing LC_GLOBAL_LOCALE to functions such as isalnum_l()
    results in undefined behavior, but applications can convert
    it into a usable locale object by using duplocale().

>> test-fcntl.c:382: assertion failed
>> FAIL: test-fcntl
> This is caused by the fact that the F_GETOWN fcntl on Linux is broken;
> there's no way to distinguish error returns from non-error negative
> return values. So we never set errno when calling F_GETOWN and assume
> the return value is not an error. There's a new-ish Linux-specific
> F_GETOWN_EX we could use when it's available, but the fallback code
> would still fail just like it does now, because it's a fundamental
> limitation in the API.

Yes, Linux 2.6.32 introduced F_GETOWN_EX for precisely this reason, and
you should be using it.

>> test-grantpt.c:34: assertion failed
>> FAIL: test-grantpt
> This is an invalid test. POSIX specifies this function "may fail", not
> "shall fail", and since the function is inherently a no-op, it would
> be idiotic to make it perform a syscall to check the validity of the
> file descriptor...

This is one of the cases where gnulib prefers to emulate the shall fail
semantics of glibc, as they are more useful to program around.

>> test-ptsname_r.c:118: assertion failed
>> FAIL: test-ptsname_r
> It's testing that ptsname_r both sets errno and returns the error
> code, and that they're the same. Since this function is nonstandard,
> there's no spec for it, so perhaps this is desirable; I was assuming
> it should return -1 on failure.

There _is_ a proposed standard for it now:

which requires only the return value to be 0 or an errno value, and not
that errno be set.  gnulib should only be checking for a valid return value.

>> test-strerror_r.c:118: assertion failed
>> FAIL: test-strerror_r
> This test is looking for a null terminator at the n-1 position of the
> buffer if strerror_r fails with ERANGE (buffer too small). I don't see
> anywhere the function is specified to write to the buffer AT ALL on
> failure, so this test seems invalid.

This is a case where POSIX is rather weak, but where quality of
implementation demands that the most useful interface is one that
provides the most information back to the user.  glibc had a number of
bugs that were fixed in this area to improve QoI, and gnulib now prefers
to rely on those improvements.

Eric Blake    +1-919-301-3266
Libvirt virtualization library

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