[cfe-dev] [RFC] Reliable compiler specification setting (at least include/lib dirs) through the process environment

[Shea Levy via cfe-dev]

Hi Ludo’,

Your patches look good! My biggest concern is how the ld wrapper behaves
in the presence of response files. Have you tested that?

Thanks,
Shea

Ludovic Courtès <ludo at gnu.org> writes:

> Hi Shea,
>
> Shea Levy skribis:
>
>> Unlike the traditional approach of installing system libraries into one
>> central location like /usr/{lib,include}, the nix package manager [1]
>> installs each package into it's own prefix
>> (e.g. /nix/store/mn9kqag3d24v6q41x747zd7n5qnalch7-zlib-1.2.8-dev). Moreover,
>> each package is built in its own environment determined from its
>> explicitly listed dependencies, regardless of what else is installed on
>> the system. Because not all package build scripts properly respect
>> CFLAGS etc., we currently wrap the compiler [2] to respect custom
>> environment variables like NIX_CFLAGS_COMPILE, so during the build of a
>> package that depends on zlib and Xlib might have NIX_CFLAGS_COMPILE set
>> to "-isystem /nix/store/bl0rz2xinsm9yslghd7n5vaba86zxknh-libX11-1.6.3-dev/include -isystem /nix/store/mn9kqag3d24v6q41x747zd7n5qnalch7-zlib-1.2.8-dev/include".
>>
>> Unfortunately, as you can see if you click through the link or look
>> through the git history, the wrapper is quite complex (frankly, hacky)
>
>> [2]: https://github.com/NixOS/nixpkgs/blob/8cbdd9d0c290e294a9d783c8868e738db05c9ce2/pkgs/build-support/cc-wrapper/cc-wrapper.sh
>
> Guix avoids the compiler wrapper altogether like this:
>
>   • We use C_INCLUDE_PATH, LIBRARY_PATH, and friends:
>     <http://git.savannah.gnu.org/cgit/guix.git/tree/gnu/packages/gcc.scm#n296>.
>
>   • We have a simple linker wrapper aimed at adding -Wl,-rpath flags:
>     <http://git.savannah.gnu.org/cgit/guix.git/tree/gnu/packages/ld-wrapper.in#n42>.
>     The comment in that file explains why the other options considered
>     were unsuitable.
>
>   • We modify the built-in “lib” spec of GCC to add the necessary -L and
>     -rpath flags:
>     <http://git.savannah.gnu.org/cgit/guix.git/tree/gnu/packages/gcc.scm#n218>.
>
>   • Likewise, we tell Clang where to find libc and friends:
>     <http://git.savannah.gnu.org/cgit/guix.git/tree/gnu/packages/patches/clang-libc-search-path.patch>
>     <http://git.savannah.gnu.org/cgit/guix.git/tree/gnu/packages/llvm.scm#n161>.
>
> This is not too intrusive and more robust than wrapping everything.
>
> I suppose GCC and Clang could facilitate this by providing configure
> options to augment the “lib” spec, specify the location of libc alone,
> or something along these lines.
>
> Thoughts?
>
> Ludo’.
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