GNU bug report logs - #32767
glibc shadows gcc's C++ headers

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Maxim Cournoyer <maxim.cournoyer <at> gmail.com>
Cc: tracker <at> debbugs.gnu.org
Subject: bug#32767: closed (glibc shadows gcc's C++ headers)
Date: Tue, 09 Mar 2021 21:36:01 +0000

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Your message dated Tue, 09 Mar 2021 16:35:19 -0500
with message-id <87h7lkui20.fsf <at> gmail.com>
and subject line Re: bug#32767: glibc shadows gcc's C++ headers
has caused the debbugs.gnu.org bug report #32767,
regarding glibc shadows gcc's C++ headers
to be marked as done.

(If you believe you have received this mail in error, please contact
help-debbugs <at> gnu.org.)


-- 
32767: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=32767
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From: Robin Templeton <robin <at> igalia.com>
To: bug-guix <at> gnu.org
Subject: glibc shadows gcc's C++ headers
Date: Tue, 18 Sep 2018 20:32:17 -0400

When compiling C++ programs, glibc's include directory takes precedence
over gcc's for standard C headers like math.h, but glibc's headers
aren't completely compatible with C++. For example, isnan from math.h is
supposed to be a function, but glibc defines it as a macro.

This program demonstrates the problem:

#include <math.h>
int main(void) { int isnan(0); return isnan; }

It works as expected when gcc's built-in C++ headers are used, but not
if glibc is installed:

% guix environment --pure --ad-hoc gcc -- g++ -E isnan.cpp | tail -n1 
int main (void) { int isnan (0); return isnan; }
% guix environment --pure --ad-hoc gcc glibc -- g++ -E isnan.cpp | tail -n1
int main (void) { int __builtin_isnan (0); return isnan; }

As a temporary workaround, I'm using the following package as a
replacement for glibc, to keep the glibc headers out of $CPATH. If it's
installed along with gcc, ld-wrapper and binutils, the test program
compiles without errors.

(use-modules (guix) (gnu))
(use-package-modules base)
(package
  (inherit glibc)
  (name "my-glibc")
  (arguments
   (substitute-keyword-arguments (package-arguments glibc)
     ((#:phases phases)
      `(modify-phases ,phases
         (add-after 'install 'move-include
           (lambda _
             (rename-file (string-append %output "/include")
                          (string-append %output "/include-glibc"))
             #t)))))))

[Message part 3 (message/rfc822, inline)]

From: Maxim Cournoyer <maxim.cournoyer <at> gmail.com>
To: Robin Templeton <robin <at> igalia.com>
Cc: 32767-done <at> debbugs.gnu.org
Subject: Re: bug#32767: glibc shadows gcc's C++ headers
Date: Tue, 09 Mar 2021 16:35:19 -0500

Hello,

Robin Templeton <robin <at> igalia.com> writes:

> When compiling C++ programs, glibc's include directory takes precedence
> over gcc's for standard C headers like math.h, but glibc's headers
> aren't completely compatible with C++. For example, isnan from math.h is
> supposed to be a function, but glibc defines it as a macro.
>
> This program demonstrates the problem:
>
> #include <math.h>
> int main(void) { int isnan(0); return isnan; }
>
> It works as expected when gcc's built-in C++ headers are used, but not
> if glibc is installed:
>
> % guix environment --pure --ad-hoc gcc -- g++ -E isnan.cpp | tail -n1 
> int main (void) { int isnan (0); return isnan; }
> % guix environment --pure --ad-hoc gcc glibc -- g++ -E isnan.cpp | tail -n1
> int main (void) { int __builtin_isnan (0); return isnan; }
>
> As a temporary workaround, I'm using the following package as a
> replacement for glibc, to keep the glibc headers out of $CPATH. If it's
> installed along with gcc, ld-wrapper and binutils, the test program
> compiles without errors.
>
> (use-modules (guix) (gnu))
> (use-package-modules base)
> (package
>   (inherit glibc)
>   (name "my-glibc")
>   (arguments
>    (substitute-keyword-arguments (package-arguments glibc)
>      ((#:phases phases)
>       `(modify-phases ,phases
>          (add-after 'install 'move-include
>            (lambda _
>              (rename-file (string-append %output "/include")
>                           (string-append %output "/include-glibc"))
>              #t)))))))

Thanks for the report.  Nowadays the recommended way to install the
GCC-based toolchain is to use the 'gcc-toolchain' package.  The 'gcc'
package is now even made hidden in Guix, which doesn't seem to have this
particular issue:

$ guix environment --pure --ad-hoc gcc-toolchain -- g++ -E /tmp/isnan.cpp | tail -n1
int main(void) { int isnan(0); return isnan; }

$ guix environment --pure --ad-hoc gcc-toolchain glibc -- g++ -E /tmp/isnan.cpp | tail -n1
int main(void) { int isnan(0); return isnan; }

I'm closing this issue, but feel free to open a fresh one if you still
encounter problems.

Thank you,

Maxim

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