[Bug libc/10110] Separate __STDC_* predefines from features.h

[Bug libc/10110] Separate __STDC_* predefines from features.h

[jsm28 at gcc dot gnu.org]

http://sourceware.org/bugzilla/show_bug.cgi?id=10110

--- Comment #5 from joseph at codesourcery dot com <joseph at codesourcery dot com> 2010-06-04 14:41:34 UTC ---
Subject: Re:  Separate __STDC_* predefines from features.h

On Tue, 1 Jun 2010, pasky at suse dot cz wrote:

> So this should be now marked as SUSPENDED, waiting for the gcc changes, right?

No, the GCC changes are waiting on glibc maintainer feedback - feedback on 
whether, given what I said, a libc change using a separate header only for 
__STDC_ISO_10646__ would be acceptable, or whether it will be required for 
GCC to extract the __STDC_ISO_10646__ value using fixincludes.  The basic 
GCC mechanism is needed in any case, but glibc maintainer feedback is 
awaited to determine what the next pair of patches should look like.



--- Comment #6 from Joseph Myers <jsm28 at gcc dot gnu.org> 2011-01-08 17:05:10 UTC ---
Similar use cases for the glibc change and compiler feature also apply for some
optional C1X predefines (these are quite like the use case for DFP
implementation).

* Supposing glibc does not initially when supporting C1X implement the optional
<threads.h> (which duplicates facilities already in POSIX, but with different
interfaces), __STDC_NO_THREADS__ should be predefined (for the whole
translation unit), but users should still be able to use an add-on or
third-party implementation of these functions which should be able to cause
this macro to be undefined (for the whole translation unit) when the -I option
pointing to its headers is passed.  And hardcoding knowledge in GCC that a
particular library feature is unsupported seems like a bad idea since it may
not always be unsupported.

* The optional Annex K (formerly TR 24731-1) will presumably also not be
implemented in glibc (in general those functions are of very dubious design and
utility), but again it should be possible for an add-on or separate
implementation to provide implementation of the functions and wrapper headers,
and to cause __STDC_LIB_EXT1__ to be defined when the appropriate -I option is
passed.

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[Bug libc/10110] Separate __STDC_* predefines from features.h

[drepper.fsp at gmail dot com]

http://sourceware.org/bugzilla/show_bug.cgi?id=10110

--- Comment #7 from Ulrich Drepper <drepper.fsp at gmail dot com> 2011-01-09 14:10:21 UTC ---
I've already said several times I don't want any complications.

If you update glibc you update gcc as well.  If you don't you can live with a
slightly out of date value for these irrelevant macros.  Just have the
configure script detect the value for the target system and add it to the specs
file.

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[Bug libc/10110] Separate __STDC_* predefines from features.h

[jsm28 at gcc dot gnu.org]

http://sourceware.org/bugzilla/show_bug.cgi?id=10110

Joseph Myers <jsm28 at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|SUSPENDED                   |RESOLVED
         Resolution|                            |FIXED

--- Comment #8 from Joseph Myers <jsm28 at gcc dot gnu.org> 2012-02-22 12:56:48 UTC ---
After discussion on libc-alpha this time around concluded that this change was
appropriate in principle, and then approved a revised/updated patch, that
updated patch has been committed.

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[Bug libc/10110] Separate __STDC_* predefines from features.h

[fweimer at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=10110

Florian Weimer <fweimer at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
              Flags|                            |security-

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[Bug libc/10110] New: Separate __STDC_* predefines from features.h

[jsm28 at gcc dot gnu dot org]

To support implementing the C99 requirement that the __STDC_* predefined
macros are constant throughout the translation unit (not undefined before
system headers are included and defined afterwards), glibc should put those
such macros it defines in a standalone header included from <features.h>
that is also suitable for the compiler to preinclude by default.

A glibc patch is at <http://sourceware.org/ml/libc-alpha/2009-04/txt00001.txt>
and I'll also attach it to this PR.  Note that this patch is very simple and
it should be clear that it is safe; it's the GCC patch included with the same
message <http://sourceware.org/ml/libc-alpha/2009-04/msg00005.html> that's
the more complicated side of implementing this C99 requirement.

-- 
           Summary: Separate __STDC_* predefines from features.h
           Product: glibc
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: libc
        AssignedTo: drepper at redhat dot com
        ReportedBy: jsm28 at gcc dot gnu dot org
                CC: glibc-bugs at sources dot redhat dot com


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[Bug libc/10110] Separate __STDC_* predefines from features.h

[jsm28 at gcc dot gnu dot org]

------- Additional Comments From jsm28 at gcc dot gnu dot org  2009-04-28 15:17 -------
Created an attachment (id=3913)
 --> (http://sourceware.org/bugzilla/attachment.cgi?id=3913&action=view)
glibc patch


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[Bug libc/10110] Separate __STDC_* predefines from features.h

[drepper at redhat dot com]

------- Additional Comments From drepper at redhat dot com  2009-06-16 15:31 -------
I don't like this super-complicated mechanism.  Just hardcode the values in gcc
(in the spec file or where else).  They must not change anywhere.  Then glibc
can be changed to not redefine them if they are already defined.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |WAITING


http://sourceware.org/bugzilla/show_bug.cgi?id=10110

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[Bug libc/10110] Separate __STDC_* predefines from features.h

[joseph at codesourcery dot com]

------- Additional Comments From joseph at codesourcery dot com  2009-06-16 16:20 -------
Subject: Re:  Separate __STDC_* predefines from features.h

On Tue, 16 Jun 2009, drepper at redhat dot com wrote:

> I don't like this super-complicated mechanism.  Just hardcode the values in gcc
> (in the spec file or where else).  They must not change anywhere.  Then glibc
> can be changed to not redefine them if they are already defined.

GCC could reasonably take responsibility for __STDC_IEC_559__ and 
__STDC_IEC_559_COMPLEX__, knowing that glibc implements the library parts 
of the requirements, and define a macro to indicate that it has taken 
responsibility for these macros.  (That would best be a separate macro, 
__IEC_559_MACROS_PREDEFINED__ or similar, since options such as 
-ffast-math mean the IEEE arithmetic requirements are not being followed 
and so these macros shouldn't actually be predefined when certain options 
are being used.)  But as I noted in the original patch submission this 
doesn't work so well for __STDC_ISO_10646__; that *should* change when 
glibc is updated for new versions of Unicode; I said:

    I strongly suspect that the value of __STDC_ISO_10646__ in glibc is
    out of date (the comment says Unicode 3.1 and the value is 200009L,
    but there have been subsequent changes updating glibc to Unicode 5).
    Updating this (in features.h before this patch or stdc-predef.h after
    it) is clearly independent of this patch.

I can implement a fixincludes-based approach, where the GCC build process 
extracts the value of __STDC_ISO_10646__ from the installed system headers 
(while determining __STDC_IEC_559__ and __STDC_IEC_559_COMPLEX__ directly 
based on the options passed to GCC); this would avoid glibc changes being 
needed, but make it more important to run the mkheaders script GCC 
installs to update the fixed headers when glibc is updated and an existing 
GCC installation is not rebuilt.  But the preinclusion mechanism in GCC is 
still needed for the use the DFP people wish to make of the GCC patch (I 
have confirmed they are interested in it), predefining __STDC_DEC_FP__ 
only when building with -I/usr/include/dfp to get DFP versions of headers 
(which include core glibc ones with #include_next); all the complexity 
goes in GCC (with some additional complexity to extract values at build 
time) and all you avoid is a small glibc patch to put some definitions in 
their own header.



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[Bug libc/10110] Separate __STDC_* predefines from features.h

[pasky at suse dot cz]

------- Additional Comments From pasky at suse dot cz  2010-06-01 03:58 -------
So this should be now marked as SUSPENDED, waiting for the gcc changes, right?

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|WAITING                     |SUSPENDED


http://sourceware.org/bugzilla/show_bug.cgi?id=10110

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