Re: [gentoo-dev] RFC: News item regarding c++98 vs c++11
On 20/10/14 00:53, Anthony G. Basile wrote: Hi everyone, I debated about whether to write a news item about c++11 abi. Usually our news items are about some change which requires user intervention. But this is just precautionary. With more packages needing c++11 because of source changes, we may want to inform users about breakage at the ABI level in case they do something like add -std=c++11 to their global CXXFLAGS. Let me know if you think its worth sending out and/or any other suggestions. Shorter form: Since gcc-4.7 there is a -std=c++11 option, do not use it since it breaks the ABI, resulting in a non-functional system. lu
Re: [gentoo-dev] RFC: News item regarding c++98 vs c++11
-BEGIN PGP SIGNED MESSAGE-
Hash: SHA256
On 20/10/14 08:36, Luca Barbato wrote:
Since gcc-4.7 there is a -std=c++11 option, do not use it since it
breaks the ABI, resulting in a non-functional system.
Since gcc-4.7 there is a -std=c++11 option, do not use it {+yet+}
since it breaks the ABI, resulting in a non-functional system.
- --
Alexander
berna...@gentoo.org
https://secure.plaimi.net/~alexander
-BEGIN PGP SIGNATURE-
Version: GnuPG v2
Comment: Using GnuPG with Thunderbird - http://www.enigmail.net/
iF4EAREIAAYFAlRExnsACgkQRtClrXBQc7XyIAD/du6PRahrLuVuWO2tTUuxPbOs
ttGMwOpQc6zwU6W5yOEBAJa8u2YPnJxL6v6J3DEUA+js3u22a3JAopPTcd6Fua6H
=UhZq
-END PGP SIGNATURE-
Re: [gentoo-dev] RFC: News item regarding c++98 vs c++11
On 10/20/14 04:23, Alexander Berntsen wrote:
-BEGIN PGP SIGNED MESSAGE-
Hash: SHA256
On 20/10/14 08:36, Luca Barbato wrote:
Since gcc-4.7 there is a -std=c++11 option, do not use it since it
breaks the ABI, resulting in a non-functional system.
Since gcc-4.7 there is a -std=c++11 option, do not use it {+yet+}
since it breaks the ABI, resulting in a non-functional system.
Yes. Eventually we'll have to clear the road for this. However, I
don't think we'll ever want to support a mixed abi system.
--
Anthony G. Basile, Ph.D.
Gentoo Linux Developer [Hardened]
E-Mail: bluen...@gentoo.org
GnuPG FP : 1FED FAD9 D82C 52A5 3BAB DC79 9384 FA6E F52D 4BBA
GnuPG ID : F52D4BBA
Re: [gentoo-dev] RFC: News item regarding c++98 vs c++11
On 10/19/14 19:08, Alex Xu wrote: On 19/10/14 06:53 PM, Anthony G. Basile wrote: the default is still gnu++98 what does this mean, how does it differ from c++98? Its a gnu dialect. I'm not sure of the details of how it deviates from the strict standard. I'm more familiar with how c++11 differs from c++98. Google around and let me know what you find. in the older ABI, can lead to a crippled system. what do you mean, will other packages break too? maybe may lead to non-functioning or possibly broken packages. adjust as necessary; I am not familiar with what may break if incompatible libraries are linked together. If you build a library in the other abi, then executables which link against it may fail. I say may because you might get lucky and just miss one of the changes. See https://gcc.gnu.org/wiki/Cxx11AbiCompatibility. That's only for gcc-4.7 though. I got a feeling that list is not complete. However, as c++11 gains in popularity and the number of packages using it increase, it is important that users understand these precautions. what precautions? what am I supposed to do? is there a option to warn me if I try to do something stupid? should I check some packages on my system? Do nothing. A careful reading implies that you should not just add -std=c++11 or gnu++11 to your compiler flags without knowing that things can break. I can emphasis that at this point. remember that gcc-4.7 is literally all (standard) gentoo users, so a news item needs to be clear about who exactly needs to care about the issue, which here appears to be a small subset of all (standard) gentoo users; namely, those who specifically opt in to using C++11 (or are compiling such packages manually). User fool around with stuff all the time which I like. This is a cautionary note which increases awareness especially when we get bug reports. The real question to my colleagues is whether they think this is news worthy or not. I don't want to turn it into a c++11 gentoo howto. also, strictly speaking, last I checked, the name of the standard is C++11; c++11 is just what gcc takes. and maybe some links about what could break if I link incompatible libraries together would be helpful, since the links don't seem to go over that (at least apparently; I did not read the entire contents). Basically what happens is you get unresolved symbols. You will know them because of the charactarist c++ mangled names which you can demangle with c++filt. -- Anthony G. Basile, Ph.D. Gentoo Linux Developer [Hardened] E-Mail: bluen...@gentoo.org GnuPG FP : 1FED FAD9 D82C 52A5 3BAB DC79 9384 FA6E F52D 4BBA GnuPG ID : F52D4BBA
Re: [gentoo-dev] RFC: News item regarding c++98 vs c++11
On 10/20/14 12:53 AM, Anthony G. Basile wrote: GCC 4.7 introduced the new experimental 2011 ISO C++ standard [1], along with its GNU variant. This new standard is not the default in GCC 4.7, 4.8 or 4.9, the default is still gnu++98, but it can be enabled by passing -std=c++11 or -std=gnu++11 to CXXFLAGS. Users that wish to try c++11 should exercise caution because it is not ABI-compatible with c++98. This seems to focus on the Gentoo user adding -std=c++11 to CXXFLAGS. Do we consider this #1 problem with gcc-4.8 or 4.7+? As far as I'm concerned, the big issue is e.g. https://bugs.gentoo.org/show_bug.cgi?id=513386, where having gcc-4.7 and gcc-4.8 installed on the same system (and using gcc-4.7 as the active gcc version) is known to be broken. Another concern I have with the above news item is it might actually encourage crazy users to add -std=c++11 to CXXFLAGS, even though otherwise they wouldn't even know about the flag. To summarize, my suggestion is to make sure we clearly communicate known bugs reported to Gentoo, like example above one. Paweł signature.asc Description: OpenPGP digital signature
Re: [gentoo-dev] RFC: News item regarding c++98 vs c++11
-BEGIN PGP SIGNED MESSAGE-
Hash: SHA256
On 20/10/14 06:58 AM, Anthony G. Basile wrote:
On 10/20/14 04:23, Alexander Berntsen wrote:
-BEGIN PGP SIGNED MESSAGE- Hash: SHA256
On 20/10/14 08:36, Luca Barbato wrote:
Since gcc-4.7 there is a -std=c++11 option, do not use it since
it breaks the ABI, resulting in a non-functional system.
Since gcc-4.7 there is a -std=c++11 option, do not use it
{+yet+} since it breaks the ABI, resulting in a non-functional
system.
Yes. Eventually we'll have to clear the road for this. However,
I don't think we'll ever want to support a mixed abi system.
Can we, even? Would it be a mixed-abi system or a multi-abi system?
-BEGIN PGP SIGNATURE-
Version: GnuPG v2
iF4EAREIAAYFAlRFVgwACgkQ2ugaI38ACPCDYwD+JWeZv7wu0Ot4VmTUJ1pzLxzq
K/vRu9vBd+oYLzZLMm0A/1VMtKXCY5yD3pRJJKMB+Wx+g/1jN7XblluM1IIfrlNK
=1uAG
-END PGP SIGNATURE-
Re: [gentoo-dev] RFC: News item regarding c++98 vs c++11
On 10/20/14 12:21, Paweł Hajdan, Jr. wrote: On 10/20/14 12:53 AM, Anthony G. Basile wrote: GCC 4.7 introduced the new experimental 2011 ISO C++ standard [1], along with its GNU variant. This new standard is not the default in GCC 4.7, 4.8 or 4.9, the default is still gnu++98, but it can be enabled by passing -std=c++11 or -std=gnu++11 to CXXFLAGS. Users that wish to try c++11 should exercise caution because it is not ABI-compatible with c++98. This seems to focus on the Gentoo user adding -std=c++11 to CXXFLAGS. Do we consider this #1 problem with gcc-4.8 or 4.7+? As far as I'm concerned, the big issue is e.g. https://bugs.gentoo.org/show_bug.cgi?id=513386, where having gcc-4.7 and gcc-4.8 installed on the same system (and using gcc-4.7 as the active gcc version) is known to be broken. This is one step beyond the news item. In addition to the incompatibility between c++98 abi and c++11, you can expect c++11 code compiled with gcc-4.7 to not work with c++11 compiled with 4.8 and vice versa. But this is our problem, not the users'. When we start to support c++11 in full force, we may need to block earlier versions of gcc on certain packages to avoid the above mismatch, maintain patches, etc. Its premature to say. Another concern I have with the above news item is it might actually encourage crazy users to add -std=c++11 to CXXFLAGS, even though otherwise they wouldn't even know about the flag. If you tell a child don't touch! they will. I agree with you, and debated for exactly this reason, but in the end, I think its better to have a informed public. We'll get better bug reports and better co-operation. This is the problem with a form source distro. We can't control how the users will build their executables and this is one case where you can break things. To summarize, my suggestion is to make sure we clearly communicate known bugs reported to Gentoo, like example above one. I could add another sentence that the resulting abi is also gcc version dependant, but I don't want to go too far because we aren't supporting c++11 yet. Paweł -- Anthony G. Basile, Ph. D. Chair of Information Technology D'Youville College Buffalo, NY 14201 (716) 829-8197
Re: [gentoo-dev] RFC: News item regarding c++98 vs c++11
On 10/20/14 14:35, Ian Stakenvicius wrote:
-BEGIN PGP SIGNED MESSAGE-
Hash: SHA256
On 20/10/14 06:58 AM, Anthony G. Basile wrote:
On 10/20/14 04:23, Alexander Berntsen wrote:
-BEGIN PGP SIGNED MESSAGE- Hash: SHA256
On 20/10/14 08:36, Luca Barbato wrote:
Since gcc-4.7 there is a -std=c++11 option, do not use it since
it breaks the ABI, resulting in a non-functional system.
Since gcc-4.7 there is a -std=c++11 option, do not use it
{+yet+} since it breaks the ABI, resulting in a non-functional
system.
Yes. Eventually we'll have to clear the road for this. However,
I don't think we'll ever want to support a mixed abi system.
Can we, even? Would it be a mixed-abi system or a multi-abi system?
The correct thing for upstream to do is to bump the soname. But right
now, we have:
readelf -d /usr/lib/gcc/x86_64-pc-linux-gnu/4.7.3/libstdc++.so.6.0.17 |
grep SONAME
readelf -d /usr/lib/gcc/x86_64-pc-linux-gnu/4.8.2/libstdc++.so.6.0.18 |
grep SONAME
readelf -d /usr/lib/gcc/x86_64-pc-linux-gnu/4.9.1/libstdc++.so.6.0.20
| grep SONAME
all yielding
0x000e (SONAME) Library soname: [libstdc++.so.6]
--
Anthony G. Basile, Ph.D.
Gentoo Linux Developer [Hardened]
E-Mail: bluen...@gentoo.org
GnuPG FP : 1FED FAD9 D82C 52A5 3BAB DC79 9384 FA6E F52D 4BBA
GnuPG ID : F52D4BBA
Re: [gentoo-dev] RFC: News item regarding c++98 vs c++11
On 10/20/14 15:49, Anthony G. Basile wrote:
On 10/20/14 14:35, Ian Stakenvicius wrote:
-BEGIN PGP SIGNED MESSAGE-
Hash: SHA256
On 20/10/14 06:58 AM, Anthony G. Basile wrote:
On 10/20/14 04:23, Alexander Berntsen wrote:
-BEGIN PGP SIGNED MESSAGE- Hash: SHA256
On 20/10/14 08:36, Luca Barbato wrote:
Since gcc-4.7 there is a -std=c++11 option, do not use it since
it breaks the ABI, resulting in a non-functional system.
Since gcc-4.7 there is a -std=c++11 option, do not use it
{+yet+} since it breaks the ABI, resulting in a non-functional
system.
Yes. Eventually we'll have to clear the road for this. However,
I don't think we'll ever want to support a mixed abi system.
Can we, even? Would it be a mixed-abi system or a multi-abi system?
The correct thing for upstream to do is to bump the soname. But right
now, we have:
readelf -d /usr/lib/gcc/x86_64-pc-linux-gnu/4.7.3/libstdc++.so.6.0.17 |
grep SONAME
readelf -d /usr/lib/gcc/x86_64-pc-linux-gnu/4.8.2/libstdc++.so.6.0.18 |
grep SONAME
readelf -d /usr/lib/gcc/x86_64-pc-linux-gnu/4.9.1/libstdc++.so.6.0.20
| grep SONAME
all yielding
0x000e (SONAME) Library soname: [libstdc++.so.6]
Oh wait sorry, that's a confusion with the gcc-4.7 vs 4.8 problem. As
far as the c++98 vs c++11, I'm not sure.
--
Anthony G. Basile, Ph. D.
Chair of Information Technology
D'Youville College
Buffalo, NY 14201
(716) 829-8197
[gentoo-dev] RFC: News item regarding c++98 vs c++11
Hi everyone, I debated about whether to write a news item about c++11 abi. Usually our news items are about some change which requires user intervention. But this is just precautionary. With more packages needing c++11 because of source changes, we may want to inform users about breakage at the ABI level in case they do something like add -std=c++11 to their global CXXFLAGS. Let me know if you think its worth sending out and/or any other suggestions. Title: GCC 4.7 Introduces New c++11 ABI Author: Anthony G. Basile bluen...@gentoo.org Content-Type: text/plain Posted: 2014-10-20 Revision: 1 News-Item-Format: 1.0 Display-If-Installed: =sys-devel/gcc-4.7.0 Display-If-Keyword: amd64 Display-If-Keyword: arm Display-If-Keyword: mips Display-If-Keyword: ppc Display-If-Keyword: ppc64 Display-If-Keyword: x86 Display-If-Keyword: amd64-fbsd Display-If-Keyword: x86-fbsd GCC 4.7 introduced the new experimental 2011 ISO C++ standard [1], along with its GNU variant. This new standard is not the default in GCC 4.7, 4.8 or 4.9, the default is still gnu++98, but it can be enabled by passing -std=c++11 or -std=gnu++11 to CXXFLAGS. Users that wish to try c++11 should exercise caution because it is not ABI-compatible with c++98. Thus linking c++98 and c++11 objects is likely to cause breakage. For packages which are self-contained and do not link against any libraries written in C++, there is no problem. However, switching to c++11 and then building packages which link against any of the numerous libraries still in the older ABI, can lead to a crippled system. This is a precautionary news item and the typical user need not do anything. However, as c++11 gains in popularity and the number of packages using it increase, it is important that users understand these precautions. For an ABI compliance checker, and more information about C++ ABIs, see [2]. Ref. [1] http://www.stroustrup.com/C++11FAQ.html [2] http://ispras.linuxbase.org/index.php/ABI_compliance_checker -- Anthony G. Basile, Ph.D. Gentoo Linux Developer [Hardened] E-Mail: bluen...@gentoo.org GnuPG FP : 1FED FAD9 D82C 52A5 3BAB DC79 9384 FA6E F52D 4BBA GnuPG ID : F52D4BBA
Re: [gentoo-dev] RFC: News item regarding c++98 vs c++11
On Sun, 19 Oct 2014 18:53:43 -0400 Anthony G. Basile bluen...@gentoo.org wrote: we may want to inform users about breakage at the ABI level in case they do something like add -std=c++11 to their global CXXFLAGS. You mean tell them they get to keep the pieces? jer
Re: [gentoo-dev] RFC: News item regarding c++98 vs c++11
On 10/19/14 18:57, Jeroen Roovers wrote: On Sun, 19 Oct 2014 18:53:43 -0400 Anthony G. Basile bluen...@gentoo.org wrote: we may want to inform users about breakage at the ABI level in case they do something like add -std=c++11 to their global CXXFLAGS. You mean tell them they get to keep the pieces? jer Yes. I'm saying it politely. -- Anthony G. Basile, Ph.D. Gentoo Linux Developer [Hardened] E-Mail: bluen...@gentoo.org GnuPG FP : 1FED FAD9 D82C 52A5 3BAB DC79 9384 FA6E F52D 4BBA GnuPG ID : F52D4BBA
Re: [gentoo-dev] RFC: News item regarding c++98 vs c++11
On 19/10/14 06:53 PM, Anthony G. Basile wrote: the default is still gnu++98 what does this mean, how does it differ from c++98? in the older ABI, can lead to a crippled system. what do you mean, will other packages break too? maybe may lead to non-functioning or possibly broken packages. adjust as necessary; I am not familiar with what may break if incompatible libraries are linked together. However, as c++11 gains in popularity and the number of packages using it increase, it is important that users understand these precautions. what precautions? what am I supposed to do? is there a option to warn me if I try to do something stupid? should I check some packages on my system? remember that gcc-4.7 is literally all (standard) gentoo users, so a news item needs to be clear about who exactly needs to care about the issue, which here appears to be a small subset of all (standard) gentoo users; namely, those who specifically opt in to using C++11 (or are compiling such packages manually). also, strictly speaking, last I checked, the name of the standard is C++11; c++11 is just what gcc takes. and maybe some links about what could break if I link incompatible libraries together would be helpful, since the links don't seem to go over that (at least apparently; I did not read the entire contents). signature.asc Description: OpenPGP digital signature
