Wookey, the short answer is 'yes'. The next question is 'who?'. Maybe this can be bolted onto the hard float work, I'll let Konstantinos and Steve respond... Dave
On 06/01/11 01:22, Wookey wrote:
[Apologies for the wide distibution of this mail (Debian, Ubuntu and Fedora main+arm dev lists, plus linaro and lsb) but it's useful to catch people who care about this issue enough to do some work. Do please bear the distribution in mind when replying, focussing any detailed discussion on linaro-dev please. I'll post a summary at the end if there is material input]
The subject of the Linux Standards Base (LSB) and ARM came up at the recent Linaro Dev summit.
During discussion of standardisation of ABI across distributions (Ubuntu, Debian, Fedora etc) it was suggested that maybe the LSB was a useful place to specify some kind of agreed minimum.
It turns out that the LSB supports 7 architectures, but does not include ARM, beyond the catch-all 'generic'. This seemed an odd omission so I contacted the LSB people who were very helpful, and I found that they would like to support ARM but a) there was not a clear binary ABI standard to support in the past (there were lots of variants) and b) no-one really stepped up to do the work of porting the LSB docs and tools.
It came up on the LSB list too: https://lists.linux-foundation.org/pipermail/lsb-discuss/2011-May/006828.htm...
As I say in that thread, I think a) has been dealt with in that there is now an agreed base with wide-enough support that we could usefully specify (the armv7, VFP-D16 ('hard-float'), little-endian ABI, as used by Debian 'armhf', Ubuntu 'armhf', Fedora 'armv7hl', and also Meego 'armv7hl'). That fits with what Linaro is supporting too.
Mats D Wichman kindly gave some idea of how much work in needed to 'port' the LSB in the above thread:
in that range of options [week, month, year, 6 years], it's closer to a year than to any of the others.
The spec work isn't hard by itself if there's a reasonable processor-level ABI document available, which unless something has changed, is the case for ARM: like the psABI documents that exist for other architectures, reference is made to such a base document (or set) for things like register assignments, calling conventions, exception processing, etc. so it doesn't have to be written - maybe just pinning down where the base document offers choices, that the LSB ABI does it this way.
In addition to the spec, there's a great deal of code around LSB, which all has to be adapted. It's obviously portable code since it works for seven architectures already, of varying wordsizes, endian-ness, etc. Where there are details specific to a processor architecture, we actually have all of the details stored in a database (which can be browsed at http://dev.linuxfoundation.org/navigator), and the biggest task actually becomes populating the database with data for this new architecture. There are some fairly reasonable tools for scanning a distribution which would provide a useful starting point, but then someone has to validate that things are all correct. Some of the validation happens by building and running iteratively various checkers which are part of the software suite anyway. That will require adjusting a number of makefiles, populating new trees under arch-specific names, etc. but that part is easy enough, just manual work. It has been rather a long time since a new architecture was added, I think PPC64 and S390X were added at about the same time and it was many years ago), so the procedure hasn't really been tested out recently.
Then there are a bunch of test suites which need to run to validate that a distribution conforms, and in my experience, this ends to be where new issues show up that break the assumption that everything's clean and portable, so there may well be extra debugging here.
As this is a non-trivial amount of work, the question then arises, does anyone care about this enough to actually do the work? Linaro is an obvious organisation that could expend some engineering effort on this, but to do that it needs some indication that it's more than a 'would-be-nice'.
Who actually uses the LSB for making widely-distributed binaries? Would anyone do so on ARM if it was specced? Is it important to make ARM a 'real' architecture alongside the others, e.g. especially in server space?
In my experience anyone distributing binaries actually picks a small set of distros and builds for those explicitly, rather than relying on the LSB. Does that mean that it's not actually useful in the real world? I guess in a sense this posting is to the wrong lists; we're all free software people here who have little use for the LSB. Where do the proprietary software distributors hang out :-)
It's easy to think of potential use-cases, and I think ultimately, unless the LSB is in fact entirely irrelevant, this work will get done everntually. But should we get on with that now, rather than whatever else we might be fixing, and if so, who is volunteering to get involved?
( Jon Masters and I have both expressed interest but are not exactly brimming over with spare time. Any more for any more?)
Opinions welcome.
Wookey