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gnu: gcc-6: Use libstdc++ headers appropriate for each GCC.

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After the "hack" introduced for <https://issues.guix.gnu.org/42392>, all GCCs
are built with the current GCC's libstdc++ headers.  This results in subtly
broken C++ headers in older versions, which aren't necessarily compatible with
libstdc++s from other versions.

For example, this test case works with GCC 11:

    $ guix shell --container --emulate-fhs --pure -e '(@ (gnu packages gcc) gcc)' binutils -- sh -c 'echo -e "#include <cmath>\nint main() { return std::isnan(0); }" | g++ -x c++ -; echo $?'
    0

but fails with GCC 9:

    $ guix shell --container --emulate-fhs --pure -e '(@ (gnu packages gcc) gcc-9)' binutils -- sh -c 'echo -e "#include <cmath>\nint main() { return std::isnan(0); }" | g++ -x c++ -; echo $?'

    In file included from /gnu/store/gkh2rljdrnj24q1q7baa6bhb119251w4-profile/include/c++/cmath:45,
                     from <stdin>:1:
    <stdin>: In function 'int main()':
    <stdin>:2:26: error: '__builtin_isnan' is not a member of 'std'; did you mean '__builtin_isnan'?
    <built-in>: note: '__builtin_isnan' declared here
    1

This specific error can be traced back to the GCC build, where GCC 10 and 11
are configured with:

    checking for ISO C99 support in <math.h> for C++11... yes

but GCC 9 is configured with:

    checking for ISO C99 support in <math.h> for C++11... no

The configure check fails due to errors like these due to the mismatched
libstdc++:

    configure:17817: checking for ISO C99 support in <math.h> for C++11
    […]
    In file included from /gnu/store/y3kk0ybf7hqwndl8xpm61r4a5b3lhwix-libstdc++-11.4.0/include/cmath:41,
                     from /gnu/store/y3kk0ybf7hqwndl8xpm61r4a5b3lhwix-libstdc++-11.4.0/include/math.h:36,
                     from conftest.cpp:41:
    /gnu/store/y3kk0ybf7hqwndl8xpm61r4a5b3lhwix-libstdc++-11.4.0/include/bits/c++config.h:491:18: error: missing binary operator before token "("
      491 | #if __has_builtin(__builtin_is_constant_evaluated)
          |                  ^

Updating libstdc++ to reference each GCC works around this.

* gnu/packages/gcc.scm (libstdc++, libstdc++-headers): Remove variables.
(make-libstdc++-headers): New procedure.
(gcc-6)[native-inputs]: Use it with `this-package'.

Change-Id: Ie05878c83860c4ccc29d66b916d11613e367e142
Signed-off-by: Ludovic Courtès <ludo@gnu.org>
Modified-by: Ludovic Courtès <ludo@gnu.org>
This commit is contained in:
Leo Nikkilä 2025-01-17 05:08:49 +02:00 • committed by Andreas Enge
parent c6e3584e8d
commit c4a100f3c6
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1 changed files with 25 additions and 25 deletions
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14
gnu/packages/gcc.scm
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@ -18,6 +18,7 @@
;;; Copyright © 2023 Maxim Cournoyer <maxim.cournoyer@gmail.com>
;;; Copyright © 2024 Nguyễn Gia Phong <mcsinyx@disroot.org>
;;; Copyright © 2025 Janneke Nieuwenhuizen <janneke@gnu.org>
;;; Copyright © 2025 Leo Nikkilä <hello@lnikki.la>
;;;
;;; This file is part of GNU Guix.
;;;
@ -53,6 +54,7 @@
#:use-module (gnu packages perl)
#:use-module (guix packages)
#:use-module (guix download)
#:use-module (guix memoization)
#:use-module (guix build-system gnu)
#:use-module (guix build-system trivial)
#:use-module (guix gexp)
@ -579,7 +581,7 @@ Go. It also includes runtime support libraries for these languages.")
;; XXX: This gross hack allows us to have libstdc++'s <bits/c++config.h>
;; in the search path, thereby avoiding misconfiguration of libstdc++:
;; <https://bugs.gnu.org/42392>.
("libstdc++" ,libstdc++-headers)
("libstdc++" ,(make-libstdc++-headers this-package))
,@(package-inputs gcc-4.7)))))
@ -1127,16 +1129,14 @@ using compilers other than GCC."
(propagated-inputs '())
(synopsis "GNU C++ standard library")))
(define libstdc++
;; Libstdc++ matching the default GCC.
(make-libstdc++ gcc))
(define libstdc++-headers
(define make-libstdc++-headers
(mlambdaq (gcc) ;memoize to play well with the object cache
;; XXX: This package is for internal use to work around
;; <https://bugs.gnu.org/42392> (see above). The main difference compared
;; to the libstdc++ headers that come with 'gcc' is that <bits/c++config.h>
;; is right under include/c++ and not under
;; include/c++/x86_64-unknown-linux-gnu (aka. GPLUSPLUS_TOOL_INCLUDE_DIR).
(let ((libstdc++ (make-libstdc++ gcc)))
(package
(inherit libstdc++)
(name "libstdc++-headers")
@ -1150,7 +1150,7 @@ using compilers other than GCC."
(symlink (string-append libstdc++ "/include")
(string-append out "/include/c++")))))
(inputs `(("libstdc++" ,libstdc++)))
(synopsis "Headers of GNU libstdc++")))
(synopsis "Headers of GNU libstdc++")))))
(define-public libstdc++-4.9
(make-libstdc++ gcc-4.9))