[gentoo-user] Multilib wrapped headers with amd64/no-multilib profile?

[Alexei Colin]

Hi,

In Gentoo Prefix on amd64 host with a no-multilib profile, for
packages that inherit multilib multilib-minimal, the multilib-build
eclass wraps headers as if multilib were enabled.

One example is mpi.h header in sys-cluster/openmpi. I am using a custom
modified ebuild, but the differences shouldn't be relevant to this issue.

The wrapper is causing problems for me, for reasons that are not
relevant here [1]. This question here is whether the wrapping should
takes place at all with no-multilib profile.

Wrapping happens on amd64 with this profile:
gentoo:default/linux/amd64/17.1/no-multilib/prefix/kernel-3.2+

For reference, as expected, no wrapping happens on ppc64le with:
gentoo:default/linux/ppc64le/17.0/prefix/kernel-3.2+

The above profile is a parent of my custom profile but this shouldn't be
relevant, the custom profile is simple, it just sets compiler flags,
package lists, use flags.

Diagnosis: multilib-build.eclass wrapps the headers because it is
detecting the "abi_flag" as set. So, as far as I understand, it
(wrongly?) ends up on the code path for yes-multilib instead of
no-multilib:

    multilib_prepare_wrappers()
        ...
      if [[ ${MULTILIB_WRAPPED_HEADERS[@]} ]]; then
	# If abi_flag is unset, then header wrapping is unsupported on
	# this ABI. This means the arch doesn't support multilib at all
	# -- in this case, the headers are not wrapped and everything
	# works as expected.
	^ I want the case described in this comment, but not happening
        if [[ ${MULTILIB_ABI_FLAG} ]]; then 
               ^ this is set to abi_x86_64.amd64...

...because MULTIBUILD_VARIANT is set
...because MULTIBUILD_VARIANTS contains the flag
...because multilib_get_enabled_abi_pairs() adds it there
...because 'use abi_x86_64' evaluates to true
...presumably because in gentoo/profies/sarch/amd64/
    A. use.force contains abi_x86_64, and/or
    B. make.defaults sets IUSE_IMPLICIT="abi_x86_64"

Workaround: override in my derived profile:
    1. in make.defaults: USE="-abi_x86_64"
    2. in use.force: -abi_x86_64
Then, 'use abi_x86_64' evals to false and the header is not wrapped.

Before digging deeper, I figured I'd ask whether this is by design to
end up doing multilib things with no-multilib profile, or if it's some
issue with the way the ebuild is using multilib eclasses. What is
the correct way to disable multilib for good? Thanks for any insights.

[1] The wrapper does not cover the case when Clang is passed -target
le64-unknown-unkown-unknown, which doesn't set the macros for x86_64
that the wrapper checks. I'm not faulting the wrapper, though.