Since i am not that sure about my ability to write formal specs, i am presenting my first draft for further review and suggestions for improvement.
-- Thomas Sachau Gentoo Linux Developer
For amd64 users, there is sometimes the issue, that they need 32bit libs for
certain packages (e.g.
wine or many binary-only packages). Currently, they only get them prepackaged
in binary form with
the emul-linux-x86-* packages. But those packages have a few issues (list does
not have to be complete):
-they only contain a limited set of 32bit packages
-they are precompiled, so the user cannot define his own flags
-they have to be manually maintained and updated
So the idea was to add the ability to compile 32bit packages with support from
the package manager,
so there is no need for additional packages to maintain. After this was
originally implemented, it
was further extended to allow cross-compilation for other targets, not only
limited to 32bit packages.
The basic way, how this should work:
1. Check for the current profile being multilib, this means, that the
MULTILIB_ABIS var exists and has more then 1 (space seperated) value.
Additionally, the DEFAULT_ABI var has to be defined and its content should be
part of the MULTILIB_ABIS var. Only continue with the following steps, if this
is true
2.1 Take the entries from MULTILIB_ABIS var and add a USE flag for each of them
in the form of multilib_abi_$value
2.2 Add "abiwrapper" as a USE flag
3. Check, if the package has USE=multilib enabled. Only continue with the
following steps, if this is false.
4. Add a use dependency for each USE flag added in step 2 for all dependencies
except those defined in a space seperated list of the NO_AUTO_FLAG var. The
dependency should then look like category/package[multilib_abi_$value?]
5. Find the first enabled USE flag from the list of step 2, start with
multilib_abi_$DEFAULT_ABI during the search. If none is enabled, use
multilib_abi_$DEFAULT_ABI. In the following, $ABI will reference the $value
part of the selected USE flag.
6. Before the pkg_setup phase is executed, setup the environment as following:
-export CHOST with $CHOST_$DEFAULT_ABI
-export $CC with $CHOST-gcc
-export $CXX with $CHOST-g++
-export $FC with $CHOST-gfortran
-export $CHOST with $CHOST_$ABI
-export $CBUILD with $CHOST_$ABI
-export $CDEFINE with $CDEFINE_$ABI
-export $CCASFLAGS with ${CCASFLAGS:-${CFLAGS}} and append $CFLAGS_$ABI
-export $CFLAGS with $CFLAGS and append $CFLAGS_$ABI
-export $CPPFLAGS with $CPPFLAGS and append $CPPFLAGS_$ABI
-export $CXXFLAGS with $CXXFLAGS and append $CFLAGS_$ABI
-export $FCFLAGS with $FCFLAGS and append $CFLAGS_$ABI
-export $FFLAGS with $FFLAGS and append $CFLAGS_$ABI
-export $ASFLAGS with $ASFLAGS and append $ASFLAGS_$ABI
-export $LDFLAGS with $LDFLAGS and append $CFLAGS_$ABI
-export $PKG_CONFIG_PATH with /usr/$LIBDIR_$ABI/pkgconfig
7. After src_install is finished:
7.1 Execute the following or equivalent code (prep_ml_binaries is a function
from multilib-portage from [1]):
prep_ml_binaries $(find "${D}"usr/bin "${D}"usr/sbin "${D}"bin "${D}"sbin -type
f -name '*-config' 2>/dev/null)
7.2 If USE flag abiwrapper is enabled, execute:
local noabi=()
for i in ${MULTILIB_ABIS}; do
noabi+=( ! -name '*-'${i} )
done
if use abiwrapper ; then
for i in $(find "${D}"usr/bin/ "${D}"usr/sbin "${D}"bin "${D}"sbin
-type f ${noabi[@]} 2>/dev/null); do
prep_ml_binaries "${i}"
done
fi
7.3. After src_install, do the following checks:
-is $Dusr/include not empty
-is $usr/$LIBDIR_$ABI not empty
-is abiwrapper USE flag enabled and any of /bin /usr/bin /sbin
/usr/sbin not empty
If any of those checks is true, save the content of $D to $D.$ABI. Check if
another USE flag from step 2 is enabled, if no, then continue with step 8,
otherwise reset everything to the state before pkg_setup. Find the next enabled
USE flag from step 5 and continue with that on step 6.
8. If there have been at least 2 USE flags from step 2 enabled, check if the
header files between the different target $ABIs differ. Move the files, that
dont differ, back to $D. If files differ, they are moved to
$Dusr/include/gentoo-multilib/$ABI and the following or equivalent code is
executed in $D ($ALL_ABIS is the content of $MULTILIB_ABIS, for which the USE
flags from step 2 have been enabled) (_create_abi_includes is a function from
multilib-portage from [1]):
set --
for diffabi in ${ALL_ABIS}; do
local define_var=CDEFINE_${diffabi}
set -- "$@" "${!define_var}:${dir}/gentoo-multilib/${diffabi}"
done
_create_abi_includes "$@"
Now move the rest of the content of the temporary dirs back into $D with the
content of $D.$DEFAULT_ABI being the last.
9. pkg_preinst, pkg_postinst, pkg_prerm and pkg_postrm are executed within a
loop of the following form
for each enabled USE flag from step 2 do
setup environment as described in step 6
execute phase
done
[1]:
http://git.overlays.gentoo.org/gitweb/?p=proj/portage.git;a=blob;f=bin/auto-multilib.sh;hb=refs/heads/multilib
Optional: The code from step 6, 7.1, 7.2 and 8 (for managing the headers) could
be moved into an eclass. Then the PM executes this or an equivalent internal
function with newer versions of that eclass overwrite the internal functions.
That way, those parts could be updated without the need to update change
the PMS or to wait for another EAPI for an update/change.
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