abseil: pin ABI at compile-time #7443

coryan · 2021-09-27T22:56:36Z

abseil/all

As discussed in #7400 (comment) Abseil cannot be compiled with C++11 and used from C++17, not without first "pinning" its ABI via some patches to absl/base/options.h. This PR changes the recipe to make these changes when the code is built.

Fixes #7249.

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ghost · 2021-09-27T23:12:11Z

I detected other pull requests that are modifying abseil/all recipe:

abseil: add shared option + fix link to libm + drop few patch versions + modernize #6383

This message is automatically generated by https://github.com/ericLemanissier/conan-center-conflicting-prs so don't hesitate to report issues/improvements there.

conan-center-bot · 2021-09-28T00:56:58Z

All green in build 1 (9205f3fb2702db5b9a6dd919e5a4c46e66385a3e):

abseil/20200225.3@:
All packages built successfully! (All logs)
abseil/20200205@:
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abseil/20200225.2@:
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abseil/20200923@:
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abseil/20200923.2@:
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abseil/20200923.1@:
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abseil/20210324.0@:
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abseil/20210324.1@:
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coryan · 2021-09-28T11:56:46Z

@uilianries this is the change we discussed in #7249

uilianries

Thank you!

SpaceIm · 2022-01-24T02:05:50Z

This change prevents any new build of abseil with gcc11. Why it it needed since abseil has a mechanism to detect the C++ headers to use at build and consume time? If compiler.cppstd at build and consume time are consistent and the same compiler is used, it will detect the same headers, so no ABI issue as soon as consumers either use target_compile_features() (if compiler.cppstd not set in profile) or what is injected by compiler.cppstd.
Here we are trying to assume which value to inject and it's almost impossible.

Actually the problem of function-framework-cpp comes from itself, it's here: https://github.com/GoogleCloudPlatform/functions-framework-cpp/blob/1f0e1a987472d669cb5b4323f22d2f9c07298331/CMakeLists.txt#L42-L43, it should use target_compile_features() as a good citizen, not forcing C++17 specifically.

it's almost impossible to predict if those headers are available. abseil has a mechanism to detect these headers, trust it. Since we are trying very hard to inject at build time the default C++ standard of the compiler or the one given in profile, it should be fine.

coryan · 2022-01-24T02:57:43Z

It is possible I misunderstand how this works, if so, I would be happy to learn how to handle this better.

This change prevents any new build of abseil with gcc11.

I remember reading that GCC 11 would make C++17 its default... yup, that is the case

Why it it needed since abseil has a mechanism to detect the C++ headers to use at build and consume time?

Because the headers detected at build time may be different from the headers detected at consume time, see:

#7249
abseil/abseil-cpp#696
#7400 (comment)

If compiler.cppstd at build and consume time are consistent and the same compiler is used, it will detect the same headers,

That sounds reasonable, but that is not what happened in #7400. I think the value of compiler.cppstd was empty, and therefore "the compiler default" was used. For something like GCC 10, that means Abseil was compiled with C++14, but one could try to consume it with C++17. Possibly we need a better fix now that at least one compiler uses C++17 as its default, but at the time that was the best we could think of.

so no ABI issue as soon as consumers either use target_compile_features() (if compiler.cppstd not set in profile) or what is injected by compiler.cppstd. Here we are trying to assume which value to inject and it's almost impossible.

The problem arises when Abseil is compiled with C++11 or C++14. Abseil's ABI is fixed at that point, it uses (for example) absl::string_view. Adding target_compile_features($abseil_stuff PUBLIC cxx_std_11) to Abseil will not force all consumers to use C++11, they may use C++14, C++17 , quoting cmake-compile-features(7) (emphasis mine):

In projects that use a large number of commonly available features from a particular language standard (e.g. C++ 11) one may specify a meta-feature (e.g. cxx_std_11) that requires use of a compiler mode that is at minimum aware of that standard, but could be greater.

Any consumer using C++17 will try to use std::string_view for Abseil APIs, but the binary artifacts will not have functions matching those types.

Actually the problem of function-framework-cpp comes from itself, it's here: https://github.com/GoogleCloudPlatform/functions-framework-cpp/blob/1f0e1a987472d669cb5b4323f22d2f9c07298331/CMakeLists.txt#L42-L43,
it should use target_compile_features() as a good citizen, not forcing C++17 specifically.

Most likely that would be better, it is unclear that it would solve the problem. Compiling functions-framework-cpp (and anything that consumes it) will still force the compiler to be in C++17 mode, while the compiler may have been in C++11 or C++14 mode when compiling Abseil.

SpaceIm · 2022-01-24T03:20:39Z

Yes you're right, it's a mess.
Even target_compile_features() doesn't solve it.

abseil uses (or will use) target_compile_features(<lib asbseil> PUBLIC cxx_std_11)
a downstream project like function framework may use target_compile_features(<lib> PUBLIC cxx_std_17)

So depending on compiler version, CMake injects any standard greater than C++11 while compiling abseil, then any standard greater than C++17 while consuming it in functions framework cpp.

It cannot be solved in CCI without building packages with specific compiler.cppstd in profile.

revert conan-io#7443 it's almost impossible to predict if those headers are available. abseil has a mechanism to detect these headers, trust it. Since we are trying very hard to inject at build time the default C++ standard of the compiler or the one given in profile, it should be fine.

SpaceIm · 2022-01-24T10:30:38Z

Actually there would be a solution:

enable ABSL_PROPAGATE_CXX_STD option in abseil recipe so that it uses target_compile_features(), and backport it in previous versions of abseil handled in CCI => what I did in f336e83
pin ABI just after the build of abseil (or even during the build), not before. So let it use its internal mechanism, then catch the result and edit definitions in absl/base/options with either 0 or 1 to pin the ABI in packaged headers.

Therefore, even if abseil was compiled with C++11 standard, a recipe using C++17 at consume time would not be tricked by going into the wrong branch (the opposite would not work, abseil compiled with C++17 could not work in a project forcing C++11, but in conan it shouldn't happen).

… versions + modernize * add shared option * system libs for FreeBSD and iOS/tvOS/watchOS * move checks to validate() * stop maintenance of unofficial version 20200205 * fix abseil_dll component for windows shared build * stop maintenance of unofficial version 20200205 * finer grained export of patches * drop 20200205 in config.yml as well * modernize * absl-string may link to libm * drop maintenance of several patch versions keep last patch of each "major" version * drop shared with msvc for the moment * ensure C++ standard consistency revert #7443 it's almost impossible to predict if those headers are available. abseil has a mechanism to detect these headers, trust it. Since we are trying very hard to inject at build time the default C++ standard of the compiler or the one given in profile, it should be fine.

…ew patch versions + modernize * add shared option * system libs for FreeBSD and iOS/tvOS/watchOS * move checks to validate() * stop maintenance of unofficial version 20200205 * fix abseil_dll component for windows shared build * stop maintenance of unofficial version 20200205 * finer grained export of patches * drop 20200205 in config.yml as well * modernize * absl-string may link to libm * drop maintenance of several patch versions keep last patch of each "major" version * drop shared with msvc for the moment * ensure C++ standard consistency revert conan-io#7443 it's almost impossible to predict if those headers are available. abseil has a mechanism to detect these headers, trust it. Since we are trying very hard to inject at build time the default C++ standard of the compiler or the one given in profile, it should be fine.

abseil: pin ABI at compile-time

9205f3f

ghost mentioned this pull request Sep 27, 2021

[service] Potentially conflicting recipes #3571

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ghost mentioned this pull request Sep 27, 2021

abseil: add shared option + fix link to libm + drop few patch versions + modernize #6383

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coryan marked this pull request as ready for review September 28, 2021 00:34

prince-chrismc mentioned this pull request Sep 28, 2021

Pull Requests Ready to be Reviewed prince-chrismc/conan-center-index-pending-review#1

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conan-center-bot merged commit 2139780 into conan-io:master Sep 28, 2021

coryan deleted the fix-abseil-pin-abi branch September 28, 2021 12:41

SpaceIm mentioned this pull request Dec 30, 2021

[abseil] Don't override cmake system processor #8577

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SSE4 mentioned this pull request Mar 10, 2022

[package] google-cloud-cpp/1.31.1: Does not build with gcc 11 #9679

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abseil: pin ABI at compile-time #7443

abseil: pin ABI at compile-time #7443

coryan commented Sep 27, 2021

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abseil: pin ABI at compile-time #7443

abseil: pin ABI at compile-time #7443

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