From gentoo-dev Sat Sep 22 16:48:23 2012 From: Ambroz Bizjak Date: Sat, 22 Sep 2012 16:48:23 +0000 To: gentoo-dev Subject: [gentoo-dev] RFC: method of checking for cross compilation from ebuild functions Message-Id: X-MARC-Message: https://marc.info/?l=gentoo-dev&m=134833256328617 Zac, I think you misunderstood me here. Crosscompile-only HDEPEND is definitely necessary, I've seen many packages need this. But what I'm suggesting is that we also, and maybe only, need "ROOT != /" - only HDEPEND dependencies. This means that the dependency would only be required if the package is being built for a ROOT that is not /. The idea is to eliminate the strange case that is ROOT!=/ but FEATURES has no crosscompile. If the package requires tools that it would build itself if ROOT was /, it will use the host's version of the tool whenever ROOT!=/ It wouldn't have to worry about whether the tools it builds link to libraries in ROOT. So my proposal is basically, instead of: HDEPEND="crosscompile? ( ~${CATEGORY}/${P} ) (yes, that seems to be the most common case) there would also, and maybe only, be: HDEPEND="root_not_slash? ( ~${CATEGORY}/${P} )" root_not_slash (or another name) would essentially be a superset of crosscompile, since crosscompile implies ROOT!=/. P.S. sorry Zac I sent you this twice, damn GMail :) On Sat, Sep 22, 2012 at 6:31 PM, Zac Medico wrote: > On 09/22/2012 09:08 AM, Ambroz Bizjak wrote: >> Yes, I think this is a good idea, it would allow the dependencies to >> be expressed nicely as conditions. >> >> But I'm not sure how this would be a USE flag. It should behave like >> one during the build, but it would be best if it was not written into >> the VDB as such, at least in a way that would be considered by >> --newuse. It don't want "emerge -unD" on the booted system want to >> reinstall all packages because the current ones were cross-compiled. >> Does the test flag already behave nicely like that? In that case, all >> is good, and I can try to implement this. > > Simply add your special flag to the _feature_flags variable in > config.py, and it will be exempt from --newuse. See this commit: > > http://git.overlays.gentoo.org/gitweb/?p=proj/portage.git;a=commit;h=6b19f71b39b6af43307abf20654511bace041217 > >> On a slightly different subject: I've been porting some packages to >> HDEPEND and I've seen problems with packages that want to use the >> programs they build during the build (or in postinst). Of couse this >> works for native builds, and it can be fixed to work for cross-compile >> builds (build native version or HDEPEND on host package). >> >> But what do we do with the strange case where ROOT!=/ but >> --crosscompile/FEATURES=crosscompile is not in affect? Can we expect >> that we will be able to run the programs that were built? What if they >> link to libraries only available in ROOT? >> >> So, I think it would make sense for a lot of packages to treat ROOT!=/ >> equivalently to cross-compilation, i.e. require host tool to be >> present. But with what has currently been proposed there is no >> conditional dependency on ROOT!=/, so a package cannot demand that a >> tool be present on the host. Then, it may be a good idea to add a >> conditional dependency on ROOT!=/. > > If I understand correctly, that would be like a CROSS_TDEPEND? If we > translate that to a conditional, it would become DEPEND="crosscompile? ( > foo )", since our plan was to make DEPEND apply to ROOT!=/ and HDEPEND > apply to ROOT=/, right? > >> In fact, I think that --crosscompile or FEATURES=crosscompile could >> actually be abolished and only this condition would be available. It's >> true that some packages would only use the host dependency if there's >> actual cross-compilation going on, but nothing will break. This would >> ease configuration and reduce the number of cases to be tested. > > Yeah, the split between HDEPEND and DEPEND might be enough so that you > don't need these conditionals. If you're not really sure that the > conditionals are needed, then maybe it's better to eliminate them for now. > -- > Thanks, > Zac