Re: [gentoo-dev] Re: RFC: News item regarding c++98 vs c++11
On 10/25/14 05:32, Paweł Hajdan, Jr. wrote: On 10/24/14 7:29 PM, Anthony G. Basile wrote: So I don't have to keep email the entire item to the list, how about just adding it as follows: Nor is c++11 code compiled with gcc-4.7 ABI-compatible with c++11 compiled with 4.8, and vice versa. An example can be see in ref. [2] Ref. [2] https://bugs.gentoo.org/show_bug.cgi?id=513386 I think this could still be clearer about the user/sysadmin perspective more than a developer perspective, i.e. present this more like both gcc-4.7 and 4.8 installed with 4.7 being active than not ABI-compatible with C++11 compiled with 4.8. Here's my suggested draft: -%- CUT HERE -%- GCC 4.7 introduced the new experimental 2011 ISO C++ standard [1]. Users that wish to try enabling C++11 globally (e.g. using CXXFLAGS) should exercise caution because it is not ABI-compatible with C++98. Packages which are self-contained or do not link against any libraries written in C++ are not affected. Note that some packages like www-client/chromium and net-libs/webkit-gtk among others are already using C++11 features. Even having different versions of gcc installed simultaneously might lead to problems, especially if the active version of gcc is older. Please see [2] for example known bug with webkit-gtk. It is recommended to set the latest installed version of gcc as active; some packages may work when an older version is selected, but GCC upstream provides no guarantees of C++11 ABI stability for code compiled with gcc-4.x and 4.y for any x != y [3]. Ref. [1] http://www.stroustrup.com/C++11FAQ.html [2] https://bugs.gentoo.org/show_bug.cgi?id=513386 [3] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61758 -%- CUT HERE -%- Paweł I incorporated these points, but did not replace my original language. Both perspectives are now in there. -- Anthony G. Basile, Ph. D. Chair of Information Technology D'Youville College Buffalo, NY 14201 (716) 829-8197
Re: [gentoo-dev] Re: RFC: News item regarding c++98 vs c++11
On 10/24/14 7:29 PM, Anthony G. Basile wrote: So I don't have to keep email the entire item to the list, how about just adding it as follows: Nor is c++11 code compiled with gcc-4.7 ABI-compatible with c++11 compiled with 4.8, and vice versa. An example can be see in ref. [2] Ref. [2] https://bugs.gentoo.org/show_bug.cgi?id=513386 I think this could still be clearer about the user/sysadmin perspective more than a developer perspective, i.e. present this more like both gcc-4.7 and 4.8 installed with 4.7 being active than not ABI-compatible with C++11 compiled with 4.8. Here's my suggested draft: -%- CUT HERE -%- GCC 4.7 introduced the new experimental 2011 ISO C++ standard [1]. Users that wish to try enabling C++11 globally (e.g. using CXXFLAGS) should exercise caution because it is not ABI-compatible with C++98. Packages which are self-contained or do not link against any libraries written in C++ are not affected. Note that some packages like www-client/chromium and net-libs/webkit-gtk among others are already using C++11 features. Even having different versions of gcc installed simultaneously might lead to problems, especially if the active version of gcc is older. Please see [2] for example known bug with webkit-gtk. It is recommended to set the latest installed version of gcc as active; some packages may work when an older version is selected, but GCC upstream provides no guarantees of C++11 ABI stability for code compiled with gcc-4.x and 4.y for any x != y [3]. Ref. [1] http://www.stroustrup.com/C++11FAQ.html [2] https://bugs.gentoo.org/show_bug.cgi?id=513386 [3] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61758 -%- CUT HERE -%- Paweł signature.asc Description: OpenPGP digital signature
Re: [gentoo-dev] Re: RFC: News item regarding c++98 vs c++11
HI everyone, I've update the c++ news item for your consideration. I incorporated suggestions, in particular a note about incompatibility between c++11 compiled with different version of gcc differing in minor number (eg 4.7 and 4.8). -- Anthony G. Basile, Ph. D. Chair of Information Technology D'Youville College Buffalo, NY 14201 (716) 829-8197 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. Nor is c++11 code compiled with gcc-4.7 ABI-compatible with c++11 compiled with 4.8, and vice versa. Thus linking c++98 and c++11, or c++11 compiled with different versions of gcc, is likely to cause breakage. For packages which are self-contained or 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 in an incompatible ABI can lead to a broken 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 issues. 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
Re: [gentoo-dev] Re: RFC: News item regarding c++98 vs c++11
On 24/10/14 10:31 AM, Anthony G. Basile wrote: HI everyone, I've update the c++ news item for your consideration. I incorporated suggestions, in particular a note about incompatibility between c++11 compiled with different version of gcc differing in minor number (eg 4.7 and 4.8). lgtm. also mime attachments are hard to comment on. signature.asc Description: OpenPGP digital signature
Re: [gentoo-dev] Re: RFC: News item regarding c++98 vs c++11
On 10/24/14 4:31 PM, Anthony G. Basile wrote: I've update the c++ news item for your consideration. I incorporated suggestions, in particular a note about incompatibility between c++11 compiled with different version of gcc differing in minor number (eg 4.7 and 4.8). Thanks, I think this is an improvement. I'd still prefer an explicit mention that having gcc-4.7 and 4.8 installed simultaneously leads to known breakages, especially if 4.7 is the active gcc version. The text of the news item implies this, but it's just not obvious. Also consider explicitly mentioning https://bugs.gentoo.org/show_bug.cgi?id=513386. Obviously this wouldn't be a complete list of issues, but from the CC list it's a pretty common bug. If in doubt, consider this question: what would be bad about including the info I suggested above? Paweł 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. Nor is c++11 code compiled with gcc-4.7 ABI-compatible with c++11 compiled with 4.8, and vice versa. Thus linking c++98 and c++11, or c++11 compiled with different versions of gcc, is likely to cause breakage. For packages which are self-contained or 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 in an incompatible ABI can lead to a broken 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 issues. 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 signature.asc Description: OpenPGP digital signature
Re: [gentoo-dev] Re: RFC: News item regarding c++98 vs c++11
On 10/24/14 11:31, Paweł Hajdan, Jr. wrote: On 10/24/14 4:31 PM, Anthony G. Basile wrote: I've update the c++ news item for your consideration. I incorporated suggestions, in particular a note about incompatibility between c++11 compiled with different version of gcc differing in minor number (eg 4.7 and 4.8). Thanks, I think this is an improvement. I'd still prefer an explicit mention that having gcc-4.7 and 4.8 installed simultaneously leads to known breakages, especially if 4.7 is the active gcc version. The text of the news item implies this, but it's just not obvious. Also consider explicitly mentioning https://bugs.gentoo.org/show_bug.cgi?id=513386. Obviously this wouldn't be a complete list of issues, but from the CC list it's a pretty common bug. I agree, this bug is an example of the issues we'll have to face moving forward with 4.8/4.9 and c++. I can reference it. If in doubt, consider this question: what would be bad about including the info I suggested above? You don't need to convince me. Its a good example. There's no particular reason I didn't mention it. Paweł So I don't have to keep email the entire item to the list, how about just adding it as follows: Nor is c++11 code compiled with gcc-4.7 ABI-compatible with c++11 compiled with 4.8, and vice versa. An example can be see in ref. [2] Ref. [2] https://bugs.gentoo.org/show_bug.cgi?id=513386 -- Anthony G. Basile, Ph. D. Chair of Information Technology D'Youville College Buffalo, NY 14201 (716) 829-8197
[gentoo-dev] Re: RFC: News item regarding c++98 vs c++11
Ian Stakenvicius a...@gentoo.org wrote: On 20/10/14 06:58 AM, Anthony G. Basile wrote: 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? I am afraid, we *have* to, in the moment when at least one program adds -std=c++11 or -std=gnu++11 by itself (which AFAIK chromium does; also eix does, if it can). If not all C++ dependencies of that program (e.g. chromium) are compiled with -std=c++11, you automatically get ABI-mixture. (For eix, this is not the case, since eix has no dependencies on C++ programs). That's why I am not sure whether it is a good idea to discourage users from -std=gnu++11: It might in fact even increase stability of such programs which require the new language standard, and if all programs do compile with this flag, it is completely safe.
Re: [gentoo-dev] Re: RFC: News item regarding c++98 vs c++11
On Tue, Oct 21, 2014 at 4:45 AM, Martin Vaeth mar...@mvath.de wrote: Ian Stakenvicius a...@gentoo.org wrote: On 20/10/14 06:58 AM, Anthony G. Basile wrote: 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? I am afraid, we *have* to, in the moment when at least one program adds -std=c++11 or -std=gnu++11 by itself (which AFAIK chromium does; also eix does, if it can). FYI, Chromium currently has a ban on using C++ 11 library features. I imagine that helps on a system/toolchain with C++ 98 libs. http://chromium-cpp.appspot.com/
Re: [gentoo-dev] Re: RFC: News item regarding c++98 vs c++11
On 10/21/14 4:25 PM, Mike Gilbert wrote: On Tue, Oct 21, 2014 at 4:45 AM, Martin Vaeth mar...@mvath.de wrote: Ian Stakenvicius a...@gentoo.org wrote: On 20/10/14 06:58 AM, Anthony G. Basile wrote: 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? I am afraid, we *have* to, in the moment when at least one program adds -std=c++11 or -std=gnu++11 by itself (which AFAIK chromium does; also eix does, if it can). FYI, Chromium currently has a ban on using C++ 11 library features. I imagine that helps on a system/toolchain with C++ 98 libs. http://chromium-cpp.appspot.com/ Good catch. Two more observations: 1. The ban on C++11 library features will eventually get lifted as toolchain support on all platforms improves. 2. We may be linking against C++ libraries like ICU. I'd need to check that, and in many cases it would be Gentoo-specific thing since upstream uses bundled libs by default. Paweł signature.asc Description: OpenPGP digital signature
[gentoo-dev] Re: RFC: News item regarding c++98 vs c++11
Mike Gilbert flop...@gentoo.org wrote: FYI, Chromium currently has a ban on using C++ 11 library features. I do not see how this would help to avoid the problem: If a function with the same name returns a different type in c++98 than in c++11, you could only avoid the problem by not using the function at all (neither in the c++11 code nor in the c++98 code, since each may refer to the wrong symbol). Of course, if all C++ dependencies are bundled, as is apparently the case for original chromium, the problem does not occur at all, because in this case everything just uses the c++11 library.
Re: [gentoo-dev] Re: RFC: News item regarding c++98 vs c++11
On 10/20/14 00:59, Duncan wrote: Anthony G. Basile posted on Sun, 19 Oct 2014 18:59:41 -0400 as excerpted: 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? Yes. I'm saying it politely. The news item seems to suggest that users will be fine if they switch /everything/ using C++ to the new standard, alto it might be a bit tough getting to that point, but I'd guess an emerge --emptytree @world should do it, keeping track of what breaks if anything and attempting a later remerge of that package, which is what I've done when I've gone a year or two between upgrades, for instance, and it has taken patience but has worked. I have not tested emerge -e @world and would rather not suggest anything if someone wants c++11. I plan on testing on fresh systems from our stage3's. But here it looks like the intent is to say they're on their own if they do it, even if the do it /all/ (using emptytree or the like to ensure it's all done in at least recorded dependency order), which is a quite different message than what I got from reading the news item. So if you really wish to say that people electing to try c++11 are on their own, even if they rebuild everything, the news item needs to be reworded to say that. I do not want to make this into a c++11 howto. I want people aware especially so they 1) don't inadvertantly break stuff and 2) the bug reports will be better informed. -- Anthony G. Basile, Ph. D. Chair of Information Technology D'Youville College Buffalo, NY 14201 (716) 829-8197
[gentoo-dev] Re: RFC: News item regarding c++98 vs c++11
Anthony G. Basile bluen...@gentoo.org wrote:
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.
Isn't Diego just starting a gcc-4.9 tinderbox run?
It might be worth to try with -std=gnu++11 immediately:
Most API incompatibilities which I experienced in my projects
were either name clashes (with symbols not existing yet in c++98)
or other trivial things (like some char * returns intead of
const char * returns etc.); cleanly written code is likely
to be upward compatible without any issues.
Re: [gentoo-dev] Re: RFC: News item regarding c++98 vs c++11
On Mon, Oct 20, 2014 at 9:47 AM, Martin Vaeth mar...@mvath.de wrote:
Anthony G. Basile bluen...@gentoo.org wrote:
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.
Isn't Diego just starting a gcc-4.9 tinderbox run?
It might be worth to try with -std=gnu++11 immediately:
Most API incompatibilities which I experienced in my projects
were either name clashes (with symbols not existing yet in c++98)
or other trivial things (like some char * returns intead of
const char * returns etc.); cleanly written code is likely
to be upward compatible without any issues.
Probably worth doing in general, but I think it makes sense to get rid
of all the roadblocks to getting 4.9.1 working with the old ABI first.
Now excuse me while I got try to reproduce a tinderbox failure... :)
--
Rich
[gentoo-dev] Re: RFC: News item regarding c++98 vs c++11
Anthony G. Basile posted on Sun, 19 Oct 2014 18:59:41 -0400 as excerpted: 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? Yes. I'm saying it politely. The news item seems to suggest that users will be fine if they switch /everything/ using C++ to the new standard, alto it might be a bit tough getting to that point, but I'd guess an emerge --emptytree @world should do it, keeping track of what breaks if anything and attempting a later remerge of that package, which is what I've done when I've gone a year or two between upgrades, for instance, and it has taken patience but has worked. But here it looks like the intent is to say they're on their own if they do it, even if the do it /all/ (using emptytree or the like to ensure it's all done in at least recorded dependency order), which is a quite different message than what I got from reading the news item. So if you really wish to say that people electing to try c++11 are on their own, even if they rebuild everything, the news item needs to be reworded to say that. -- Duncan - List replies preferred. No HTML msgs. Every nonfree program has a lord, a master -- and if you use the program, he is your master. Richard Stallman
