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From: Jonathan Wakely <jwakely.gcc@gmail.com>
To: "Anton Wöllert" <a.woellert@gmail.com>
Cc: "gcc@gcc.gnu.org" <gcc@gcc.gnu.org>
Subject: Re: Relation between gcc version and libstdc++ version
Date: Tue, 30 Aug 2022 18:21:22 +0100	[thread overview]
Message-ID: <CAH6eHdR3_1F5+NqF4zC6dC9a16cQ1+UcLLpPgWnHeUzt6JRJ5w@mail.gmail.com> (raw)
In-Reply-To: <CAH6eHdR25-3i1oe2xOGqzBKtY2QvTrdgafEaRdGtOGnNt8Nb2Q@mail.gmail.com>

This doesn't belong on this mailing list though, please use the gcc-help
list instead.

This list is for discussion of GCC development, not help using it.


On Tue, 30 Aug 2022, 18:20 Jonathan Wakely, <jwakely.gcc@gmail.com> wrote:

>
>
> On Tue, 30 Aug 2022, 17:53 Anton Wöllert, <a.woellert@gmail.com> wrote:
>
>> Hi Jonathan,
>>
>> thank you for your reply!
>>
>> On Tue, 2022-08-30 at 17:09 +0100, Jonathan Wakely wrote:
>> >
>> >
>> > On Tue, 30 Aug 2022, 15:48 Anton Wöllert via Gcc, <gcc@gcc.gnu.org>
>> > wrote:
>> > > If this libstdc++ is
>> > > newer than the one one the target, I get undefined references
>> > > (because
>> > > there are some newer implementation details and things like that).
>> >
>> > Then you're not telling the executable how find the new libstdc++.
>> >
>> >
>> https://gcc.gnu.org/onlinedocs/libstdc++/faq.html#faq.how_to_set_paths
>> >
>> >
>>
>> I tried to do that.  If I let the toolchain use it's own libstdc++.so,
>> then I get at runtime unresolved symbols due to the version mismatch
>> (these GLIBCXX errors). This is clear.
>>
>
>
> Which is the problem described in the above FAQ. And you should solve it
> that way. Apparently you haven't done what it says to do, because you
> wouldn't get errors if you had done it.
>
> See also the page in the manual that the FAQ links to.
>
>
>
>> If I force the toolchain to link against the older target libstdc++,
>> then I get undefined symbols at compile time, because it is still using
>> it's own shipped headers for the newer libstdc++, which have
>> implementation details that use newer "functions/symbols" that are not
>> available in the old libstdc++.
>>
>
> Yes, that won't work.
>
>
>> If I furthermore remove the shipped headers and force it to include the
>> c++ headers from the older libstdc++, then everything works out.
>>
>> But this whole "patching" seems very hacky.
>>
>> > >  Is
>> > > it possible to tell G++/GCC to use the libstdc++.so from the target
>> > > and
>> > > also to use the C++ headers (like iostream) from the target?
>> >
>> > It's possible, but unsupported and probably won't work.
>>
>> So it seems to be indeed possible, but not intended.
>>
>> >
>> > > If not, is there any reason this is hard-coded?
>> >
>> > The libstdc++ headers are tightly coupled to the GCC version, so
>> > headers from a given GCC release might not even compile with a newer
>> > or older GCC.
>>
>> I would see an argument if you're trying to compile an newer libstdc++
>> with an older gcc - but why not the other way around?
>
>
> Sometimes the old libstdc++ headers contain invalid C++ which the old GCC
> did not diagnose. A newer GCC will give errors when trying to include those
> old headers. This is uncommon, but has happened a few times.
>
>
>   C++ in general
>> tries to be very good in backward compatibility.
>> This essentially means that you can't use newer compilers with more
>> features/bugfixes to compile software for older targets.
>>
>
>
> No it doesn't. Using new compilers on older machines works fine. You just
> need to do it right.
>
>
> Is there any obvious reason this is not supported?  Clang, for example,
>> also seems to be able to compile/link against different libstdc++
>> versions.  I'm just wondering.
>
>
>
> Clang has various hacks to compile the invalid code in old libstdc++
> headers. This is necessary for compatibility, because clang doesn't control
> which libstdc++ headers are present on a system where clang gets installed.
> It has to be prepared to cope with arbitrary libstdc++ versions. That's not
> an issue for GCC, because libstdc++ is part of GCC, so if you have a given
> version of GCC, then you have the matching libstdc++ headers and libraries,
> and you can use them.
>
>
>

WARNING: multiple messages have this Message-ID
From: Jonathan Wakely <jwakely.gcc@gmail.com>
To: "Anton Wöllert" <a.woellert@gmail.com>
Cc: "gcc@gcc.gnu.org" <gcc@gcc.gnu.org>
Subject: Re: Relation between gcc version and libstdc++ version
Date: Tue, 30 Aug 2022 18:21:22 +0100	[thread overview]
Message-ID: <CAH6eHdR3_1F5+NqF4zC6dC9a16cQ1+UcLLpPgWnHeUzt6JRJ5w@mail.gmail.com> (raw)
Message-ID: <20220830172122.UPscmhuxsf-CMVejTKWCOSjkQYs8jdwK61ZbjIBry0E@z> (raw)
In-Reply-To: <CAH6eHdR25-3i1oe2xOGqzBKtY2QvTrdgafEaRdGtOGnNt8Nb2Q@mail.gmail.com>

[-- Attachment #1: Type: text/plain, Size: 3860 bytes --]

This doesn't belong on this mailing list though, please use the gcc-help
list instead.

This list is for discussion of GCC development, not help using it.


On Tue, 30 Aug 2022, 18:20 Jonathan Wakely, <jwakely.gcc@gmail.com> wrote:

>
>
> On Tue, 30 Aug 2022, 17:53 Anton Wöllert, <a.woellert@gmail.com> wrote:
>
>> Hi Jonathan,
>>
>> thank you for your reply!
>>
>> On Tue, 2022-08-30 at 17:09 +0100, Jonathan Wakely wrote:
>> >
>> >
>> > On Tue, 30 Aug 2022, 15:48 Anton Wöllert via Gcc, <gcc@gcc.gnu.org>
>> > wrote:
>> > > If this libstdc++ is
>> > > newer than the one one the target, I get undefined references
>> > > (because
>> > > there are some newer implementation details and things like that).
>> >
>> > Then you're not telling the executable how find the new libstdc++.
>> >
>> >
>> https://gcc.gnu.org/onlinedocs/libstdc++/faq.html#faq.how_to_set_paths
>> >
>> >
>>
>> I tried to do that.  If I let the toolchain use it's own libstdc++.so,
>> then I get at runtime unresolved symbols due to the version mismatch
>> (these GLIBCXX errors). This is clear.
>>
>
>
> Which is the problem described in the above FAQ. And you should solve it
> that way. Apparently you haven't done what it says to do, because you
> wouldn't get errors if you had done it.
>
> See also the page in the manual that the FAQ links to.
>
>
>
>> If I force the toolchain to link against the older target libstdc++,
>> then I get undefined symbols at compile time, because it is still using
>> it's own shipped headers for the newer libstdc++, which have
>> implementation details that use newer "functions/symbols" that are not
>> available in the old libstdc++.
>>
>
> Yes, that won't work.
>
>
>> If I furthermore remove the shipped headers and force it to include the
>> c++ headers from the older libstdc++, then everything works out.
>>
>> But this whole "patching" seems very hacky.
>>
>> > >  Is
>> > > it possible to tell G++/GCC to use the libstdc++.so from the target
>> > > and
>> > > also to use the C++ headers (like iostream) from the target?
>> >
>> > It's possible, but unsupported and probably won't work.
>>
>> So it seems to be indeed possible, but not intended.
>>
>> >
>> > > If not, is there any reason this is hard-coded?
>> >
>> > The libstdc++ headers are tightly coupled to the GCC version, so
>> > headers from a given GCC release might not even compile with a newer
>> > or older GCC.
>>
>> I would see an argument if you're trying to compile an newer libstdc++
>> with an older gcc - but why not the other way around?
>
>
> Sometimes the old libstdc++ headers contain invalid C++ which the old GCC
> did not diagnose. A newer GCC will give errors when trying to include those
> old headers. This is uncommon, but has happened a few times.
>
>
>   C++ in general
>> tries to be very good in backward compatibility.
>> This essentially means that you can't use newer compilers with more
>> features/bugfixes to compile software for older targets.
>>
>
>
> No it doesn't. Using new compilers on older machines works fine. You just
> need to do it right.
>
>
> Is there any obvious reason this is not supported?  Clang, for example,
>> also seems to be able to compile/link against different libstdc++
>> versions.  I'm just wondering.
>
>
>
> Clang has various hacks to compile the invalid code in old libstdc++
> headers. This is necessary for compatibility, because clang doesn't control
> which libstdc++ headers are present on a system where clang gets installed.
> It has to be prepared to cope with arbitrary libstdc++ versions. That's not
> an issue for GCC, because libstdc++ is part of GCC, so if you have a given
> version of GCC, then you have the matching libstdc++ headers and libraries,
> and you can use them.
>
>
>

  parent reply	other threads:[~2022-08-30 17:21 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-08-30 14:47 Anton Wöllert
2022-08-30 16:09 ` Jonathan Wakely
2022-08-30 16:09   ` Jonathan Wakely
2022-08-30 16:53   ` Anton Wöllert
2022-08-30 17:20     ` Jonathan Wakely
2022-08-30 17:20       ` Jonathan Wakely
2022-08-30 17:21       ` Jonathan Wakely [this message]
2022-08-30 17:21         ` Jonathan Wakely
2022-08-30 18:46         ` Anton Wöllert
2022-08-30 19:24           ` Jonathan Wakely
2022-08-30 19:24             ` Jonathan Wakely

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