[Bug c++/51785] New: gets not anymore declared

[Bug c++/51785] New: gets not anymore declared

[drepper.fsp at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51785

             Bug #: 51785
           Summary: gets not anymore declared
    Classification: Unclassified
           Product: gcc
           Version: 4.6.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: drepper.fsp@gmail.com


glibc 2.15 and later don't declare gets anymore for ISO C11 mode and if
_GNU_SOURCE is defined.  This causes problems with the cstdio header which
unconditionally uses

using ::gets;


Something has to be done about this.  If you want glibc to define a macro to
signal that gets is not declared let me know.  Otherwise recognize __USE_GNU.

The problem still applies to the trunk.

[Bug c++/51785] gets not anymore declared

[marc.glisse at normalesup dot org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51785

Marc Glisse <marc.glisse at normalesup dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |marc.glisse at normalesup
                   |                            |dot org

--- Comment #1 from Marc Glisse <marc.glisse at normalesup dot org> 2012-01-07 19:05:28 UTC ---
I thought this was fixed in glibc:
http://sourceware.org/bugzilla/show_bug.cgi?id=13566
?

[Bug c++/51785] gets not anymore declared

[vries at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51785

vries at gcc dot gnu.org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |vries at gcc dot gnu.org

--- Comment #2 from vries at gcc dot gnu.org 2012-01-10 22:24:10 UTC ---
(In reply to comment #1)
> I thought this was fixed in glibc:
> http://sourceware.org/bugzilla/show_bug.cgi?id=13566
> ?

AFAIU GLIBC BZ #13528 was fixed, but there is a new checkin from Ulrich which 
breaks libstdc++ build in a similar way:
...
$ git show c3a87236702cb73be1dada3438bbd3c3934e83f8
commit c3a87236702cb73be1dada3438bbd3c3934e83f8
Author: Ulrich Drepper <drepper@gmail.com>
Date:   Sat Jan 7 10:41:00 2012 -0500

    Do not declare gets in _GNU_SOURCE mode at all

diff --git a/ChangeLog b/ChangeLog
index 8f9558c..f089e19 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,7 @@
 2012-01-07  Ulrich Drepper  <drepper@gmail.com>

+       * libio/stdio.h: Do not declare gets at all for _GNU_SOURCE.
+
        * elf/tst-unique3.cc: Add explicit declaration of gets.
        * elf/tst-unique3lib.cc: Likewise.
        * elf/tst-unique3lib2.cc: Likewise.
diff --git a/libio/stdio.h b/libio/stdio.h
index d9cb573..28c98e9 100644
--- a/libio/stdio.h
+++ b/libio/stdio.h
@@ -629,7 +629,7 @@ extern char *fgets (char *__restrict __s, int __n, FILE
*__restrict __stream)
      __wur;

 #if !defined __USE_ISOC11 \
-    || (defined __cplusplus && __cplusplus <= 201103L)
+    || (defined __cplusplus && __cplusplus <= 201103L && !defined __USE_GNU)
 /* Get a newline-terminated string from stdin, removing the newline.
    DO NOT USE THIS FUNCTION!!  There is no limit on how much it will read.
...

[Bug c++/51785] gets not anymore declared

[vries at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51785

--- Comment #3 from vries at gcc dot gnu.org 2012-01-11 13:00:37 UTC ---
This attempt at 'a glibc version check and defining the std::gets prototype in
libstdc++' (PR 51773 comment 11) unbreaks the libstdc++ build:
...
Index: libstdc++-v3/include/c_std/cstdio
===================================================================
--- libstdc++-v3/include/c_std/cstdio (revision 183073)
+++ libstdc++-v3/include/c_std/cstdio (working copy)
@@ -88,6 +88,12 @@
 #undef vprintf
 #undef vsprintf

+#if __GLIBC_PREREQ (2,15)
+extern "C" {
+  extern char *gets (char *__s) __attribute__((deprecated));
+}
+#endif
+
 namespace std
 {
   using ::FILE;
Index: libstdc++-v3/include/c_global/cstdio
===================================================================
--- libstdc++-v3/include/c_global/cstdio (revision 183073)
+++ libstdc++-v3/include/c_global/cstdio (working copy)
@@ -89,6 +89,12 @@
 #undef vprintf
 #undef vsprintf

+#if __GLIBC_PREREQ (2,15)
+extern "C" {
+  extern char *gets (char *__s) __attribute__((deprecated));
+}
+#endif
+
 namespace std
 {
   using ::FILE;
...

[Bug libstdc++/51785] gets not anymore declared

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51785

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2012-01-11
          Component|c++                         |libstdc++
     Ever Confirmed|0                           |1

--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> 2012-01-11 13:25:08 UTC ---
Thanks - I can't test this myself as I don't have the latest glibc sources but
will confirm it and change component to libstdc++

Ulrich, G++ unconditionally defines _GNU_SOURCE so __USE_GNU will always be
defined when <cstdio> includes <stdio.h>, so there's no point checking for it.

I think Tom's fix is along the right lines, but we probably want to check for
the gets() declaration using autoconf and define a _GLIBCXX macro rather than
having __GLIBC_PREREQ in the headers, then do:

#ifdef _GLIBCXX_NEED_GETS_DECL
extern "C" {
  extern char *gets (char *__s) __attribute__((deprecated));
}
#endif

At some point we might need to handle the case where the underlying platform
doesn't provide gets() at all (e.g. if libstdc++ is used on a platform which
only supports C11) but that's not the case for GNU libc and we can worry about
that if/when it happens.

[Bug libstdc++/51785] gets not anymore declared

[marc.glisse at normalesup dot org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51785

--- Comment #5 from Marc Glisse <marc.glisse at normalesup dot org> 2012-01-11 13:49:54 UTC ---
If we are just going to declare gets when glibc doesn't, the easiest solution
is a fixinclude that reverts Ulrich's latest glibc commit. Somehow that doesn't
feel right...

[Bug libstdc++/51785] gets not anymore declared

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51785

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org

--- Comment #6 from Jakub Jelinek <jakub at gcc dot gnu.org> 2012-02-05 20:34:05 UTC ---
Yeah, IMHO the removal of gets (== ::gets) for _GNU_SOURCE is very much
intentional.  C++ probably only talks about std::gets, doesn't it?
So IMHO then should libstdc++ just for glibc versions that don't provide gets
prototype with _GNU_SOURCE defined instead add
namespace std
{
  char *gets (char *) __asm ("gets");
};

[Bug libstdc++/51785] gets not anymore declared

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51785

--- Comment #7 from Jonathan Wakely <redi at gcc dot gnu.org> 2012-02-05 21:00:36 UTC ---
(In reply to comment #6)
> Yeah, IMHO the removal of gets (== ::gets) for _GNU_SOURCE is very much
> intentional.  C++ probably only talks about std::gets, doesn't it?

No, std::gets must be declared by <cstdio> and ::gets must be declared by
<stdio.h>

[Bug libstdc++/51785] gets not anymore declared

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51785

--- Comment #8 from Jonathan Wakely <redi at gcc dot gnu.org> 2012-02-05 21:26:26 UTC ---
Though personally I'm not concerned if libstdc++ doesn't define gets(), noone
should be using it, I am concerned that libstdc++ fails to build because of the
using decl.

[Bug libstdc++/51785] gets not anymore declared

[ramana at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51785

Ramana Radhakrishnan <ramana at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ramana at gcc dot gnu.org,
                   |                            |rearnsha at gcc dot gnu.org

--- Comment #9 from Ramana Radhakrishnan <ramana at gcc dot gnu.org> 2012-02-28 14:41:56 UTC ---

I ran into this failure today when upgrading my copy of (e)glibc in my
cross-environment. What's the best way of progressing this further ? 

Doesn't this mean that trunk is broken for building with anything later than
glibc-2.15 ? 

Ramana

[Bug libstdc++/51785] gets not anymore declared

[joseph at codesourcery dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51785

--- Comment #10 from joseph at codesourcery dot com <joseph at codesourcery dot com> 2012-02-28 15:23:38 UTC ---
If the libstdc++ people are going to do something for 4.7, it really needs 
to be done very soon.

Let's assume glibc should at least get a further change for the sake of 
older GCC versions - changing !defined __USE_GNU to (!defined __USE_GNU || 
(defined __GNUC__ && !__GNUC_PREREQ (4, 7))).  But if this isn't fixed for 
4.7, that conditional in stdio.h would need to use __GNUC_PREREQ (4, 8) 
instead.

[Bug libstdc++/51785] gets not anymore declared

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51785

--- Comment #11 from Paolo Carlini <paolo.carlini at oracle dot com> 2012-02-28 15:35:59 UTC ---
If the release managers agree, I would be in favor of a quick fix per Comment
3, with a huge comment in the code explaining the issue. But I can't test it
right now.

[Bug libstdc++/51785] gets not anymore declared

[marc.glisse at normalesup dot org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51785

--- Comment #12 from Marc Glisse <marc.glisse at normalesup dot org> 2012-02-28 15:47:04 UTC ---
(In reply to comment #10)
> If the libstdc++ people are going to do something for 4.7, it really needs 
> to be done very soon.

The question is: what do the glibc people want? By removing the gets prototype,
they are explicitly going against the C++ standard. Seems to me that libstdc++
should respect that choice (add a test in configure to see if gets is provided,
and protect "using ::gets;" with #ifdef) and not provide gets. The alternative
is to disagree with the glibc developers and fixinclude stdio.h.

[Bug libstdc++/51785] gets not anymore declared

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51785

--- Comment #13 from Jakub Jelinek <jakub at gcc dot gnu.org> 2012-02-28 15:49:26 UTC ---
I'm ok with #c3 patch + comment if it works, using special configure macro
instead of __GLIBC_PREREQ is IMHO undesirable, because then if you build gcc
against glibc 2.14 and afterwards upgrade glibc to 2.15, it will suddenly
break.

[Bug libstdc++/51785] gets not anymore declared

[ramana at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51785

--- Comment #14 from Ramana Radhakrishnan <ramana at gcc dot gnu.org> 2012-02-28 16:09:52 UTC ---
I can confirm that a build for arm-linux-gnueabi completes and do some
cross-testing on qemu if that's deemed to be enough.

Any other ideas for testing. 

Ramana

Here's a suggestion for the comments in this patch. 

diff --git a/libstdc++-v3/include/c_global/cstdio
b/libstdc++-v3/include/c_global/cstdio
index 049704d..76755ac 100644
--- a/libstdc++-v3/include/c_global/cstdio
+++ b/libstdc++-v3/include/c_global/cstdio
@@ -89,6 +89,17 @@
 #undef vprintf
 #undef vsprintf

+/* glibc 2.15 and later do not declare gets anymore for 
+   ISO C11 mode and if __GNU_SOURCE is defined. See 
+   http://gcc.gnu.org/PR51785 for more on this topic. If
+   this is being changed an equivalent change has to be made
+   in include/c_std/c_stdio.  */
+#if __GLIBC_PREREQ (2,15)
+extern "C" {
+  extern char *gets (char *__s) __attribute__((deprecated));
+}
+#endif
+
 namespace std
 {
   using ::FILE;
diff --git a/libstdc++-v3/include/c_std/cstdio
b/libstdc++-v3/include/c_std/cstdio
index 510f599..29142bb 100644
--- a/libstdc++-v3/include/c_std/cstdio
+++ b/libstdc++-v3/include/c_std/cstdio
@@ -88,6 +88,17 @@
 #undef vprintf
 #undef vsprintf

+/* glibc 2.15 and later do not declare gets anymore for
+   ISO C11 mode and if __GNU_SOURCE is defined. See 
+   http://gcc.gnu.org/PR51785 for more on this topic. If
+   this hunk below is being changed please also investigate
+   the change for include/c_global/cstdio.  */
+#if __GLIBC_PREREQ (2,15)
+extern "C" {
+  extern char *gets (char *__s) __attribute__((deprecated));
+}
+#endif
+
 namespace std
 {
   using ::FILE;

[Bug libstdc++/51785] gets not anymore declared

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51785

--- Comment #15 from Jakub Jelinek <jakub at gcc dot gnu.org> 2012-02-28 16:18:30 UTC ---
Ideally, when using
#define _GNU_SOURCE
#include <stdio.h>

in a C++ program ::gets wouldn't be available (the _GNU_SOURCE requests GNU
namespace rather than standard C++ one), but when using
#include <list>
#include <stdio.h>
it would provide it (with deprecated attribute), because then the user didn't
request _GNU_SOURCE.  But for that we'd need some new macro to request
additional prototype for STL needs.

[Bug libstdc++/51785] gets not anymore declared

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51785

--- Comment #16 from Paolo Carlini <paolo.carlini at oracle dot com> 2012-02-28 16:42:55 UTC ---
I suppose that post 4.7.0 we have to revisit this issue anyway, because C++11
definitely wants to declare std::gets, irrespective of C11. I'm wondering if it
would be possible to just take this into account in <stdio.h>, I seem to
remember that the glibc headers in a few places already use __cplusplus, right?
We also have the __CORRECT_ISO_CPP_STRING_H_PROTO story as an example of
interaction between glibc and C++.

That said, for 4.7.0, I think that in any case we want: 1- To fully run the
testsuite on a GNU/Linux system using glibc2.15; 2- Convince ourselves that
whatever we do in the C++ library is not going to interact badly with further
tweaks at the glibc level..

[Bug libstdc++/51785] gets not anymore declared

[joseph at codesourcery dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51785

--- Comment #17 from joseph at codesourcery dot com <joseph at codesourcery dot com> 2012-02-28 17:05:50 UTC ---
2.15 has the gets prototype.  It's 2.16 where it has been removed (but the 
version in the headers only changes from 2.15 to 2.16 when the final 2.16 
release is made so you can't distinguish 2.15 from 2.16 development 
versions simply by examining preprocessor macros).

[Bug libstdc++/51785] gets not anymore declared

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51785

--- Comment #18 from Paolo Carlini <paolo.carlini at oracle dot com> 2012-02-28 18:25:54 UTC ---
Ah, thanks Joseph. Thus, to repeat, anything we do in terms of macros has to be
for *2.16* and later.

[Bug libstdc++/51785] gets not anymore declared

[bkoz at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51785

--- Comment #19 from Benjamin Kosnik <bkoz at gcc dot gnu.org> 2012-03-01 00:21:11 UTC ---
Created attachment 26794
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=26794
gets conditionally declared/used


Here's a way to deal with gets that is pretty simple. If it's around at
configure time, it's used. If not, it's dropped from <cstdio>. This uses the
same configure bits and approach used for math.

This should prevent any compile error at bootstrap time. That seems sufficient
for gcc-4.7 release. RMs?

Note, I'm on f17 and I'm not running into this during make/check of trunk gcc. 
If somebody can give me self-contained sources that fail on f17 it would be
appreciated.

Please don't put in GLIBC macros to cstdio. Boo.

Instead, if you need to layer on a glibc part to this, you should start with
this patch, and then conditionally define/undefine _GLIBCXX_HAVE_GETS in 

libstdc++-v3/config/os/gnu-linux/os_defines.h

based on the glibc prerequisites and version checks.

-benjamin

[Bug libstdc++/51785] gets not anymore declared

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51785

--- Comment #20 from Jakub Jelinek <jakub at gcc dot gnu.org> 2012-03-01 13:30:26 UTC ---
f17 doesn't include glibc 2.16, just patched glibc 2.15, which doesn't have
these header changes yet.
The thing I don't like on the last patch is that it hardcodes configure time
tests, so when glibc is upgraded say from 2.15 to 2.16, but gcc isn't upgraded,
suddenly anything that includes <cstdio> fails to compile.
So I'd prefer something like #c14 patch instead, perhaps testing a macro that
is
depending on __GLIBC_PREREQ defined in linux os-defines.h.

Can you please resolve this either way till tomorrow noon UTC (4.7
branching/4.7.0-rc1)?
Thanks.

[Bug libstdc++/51785] gets not anymore declared

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51785

Richard Guenther <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |rguenth at gcc dot gnu.org

--- Comment #21 from Richard Guenther <rguenth at gcc dot gnu.org> 2012-03-01 13:44:39 UTC ---
Wouldn't an unconditional

#if _GNU_SOURCE
  extern char *gets (char *__s);
  using ::gets;
#endif

work as well?

alternatively the FE could provide a language extension that would allow

  __using_if_available ::gets;

;)

Anyway, we don't need to rush anything for 4.7.0, fixing this for 4.7.1
and in a correct way is enough IMHO.

[Bug libstdc++/51785] gets not anymore declared

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51785

--- Comment #22 from Jonathan Wakely <redi at gcc dot gnu.org> 2012-03-01 13:50:57 UTC ---
(In reply to comment #21)
> Wouldn't an unconditional
> 
> #if _GNU_SOURCE
>   extern char *gets (char *__s);
>   using ::gets;
> #endif
> 
> work as well?

extern "C" or extern "C++" ?

What if someone defines _GNU_SOURCE on a non-glibc platform (maybe defined
unconditionally in a makefile, expecting it to do nothing) but it causes gets()
to be declared with a different language linkage to the one in the system's
stdio.h?

[Bug libstdc++/51785] gets not anymore declared

[bkoz at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51785

Benjamin Kosnik <bkoz at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
  Attachment #26794|0                           |1
        is obsolete|                            |

--- Comment #23 from Benjamin Kosnik <bkoz at gcc dot gnu.org> 2012-03-02 06:30:29 UTC ---
Created attachment 26807
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=26807
gets conditionally declared/used  v2


As per Jakub's comments. Since time is an issue I'm going to check this in
after regression tests complete.

[Bug libstdc++/51785] gets not anymore declared

[bkoz at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51785

--- Comment #24 from Benjamin Kosnik <bkoz at gcc dot gnu.org> 2012-03-02 07:14:02 UTC ---
Author: bkoz
Date: Fri Mar  2 07:13:55 2012
New Revision: 184774

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=184774
Log:
2012-03-01  Benjamin Kosnik  <bkoz@redhat.com>
            Ramana Radhakrishnan <ramana@gcc.gnu.org>

    PR libstdc++/51785
    * acinclude.m4 (GLIBCXX_CHECK_STDIO_PROTO): New.
    * configure.ac: Call it.
    * configure: Regenerate.
    * config.h.in: Same.
    * config/os/gnu-linux/os_defines.h: Conditionally undefine
    _GLIBCXX_HAVE_GETS.
    * include/c_global/cstdio: Conditionally declare deprecated gets.
    * include/c_std/cstdio: Same.

Modified:
    trunk/libstdc++-v3/ChangeLog
    trunk/libstdc++-v3/acinclude.m4
    trunk/libstdc++-v3/config.h.in
    trunk/libstdc++-v3/config/os/gnu-linux/os_defines.h
    trunk/libstdc++-v3/configure
    trunk/libstdc++-v3/configure.ac
    trunk/libstdc++-v3/include/c_global/cstdio
    trunk/libstdc++-v3/include/c_std/cstdio

[Bug libstdc++/51785] gets not anymore declared

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51785

--- Comment #25 from Jakub Jelinek <jakub at gcc dot gnu.org> 2012-03-02 07:29:29 UTC ---
extern "C" extern

(twice) - too many externs?

[Bug libstdc++/51785] gets not anymore declared

[jsm28 at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51785

--- Comment #26 from Joseph S. Myers <jsm28 at gcc dot gnu.org> 2012-03-09 22:13:49 UTC ---
The __USE_GNU conditional has now been removed from glibc after further
discussion on libc-alpha, so the libstdc++ changes can be reverted (probably
after 4.7.0).

[Bug libstdc++/51785] gets not anymore declared

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51785

--- Comment #27 from Paolo Carlini <paolo.carlini at oracle dot com> 2012-03-09 23:48:17 UTC ---
Thanks a lot Joseph, a very good solution.

[Bug libstdc++/51785] gets not anymore declared

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=51785

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

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

--- Comment #31 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
I don't think there is any thing more to fix here.  gets works correctly as far
as I Know.