[llvm-dev] Porting libxar to LLVM

Fri Apr 30 09:22:29 PDT 2021

I will say XAR is a very specific format for AppStore submission. Is there any reason you want to replicate the same format on other platforms? Is your goal to build and create AppStore submission from a Windows machine? That is the only reason I think of why you want to port libxar implementation. Otherwise, XAR is in the system for macOS and can probably be an optional configuration for other platforms. 

If you just want a general way to package up a bitcode bundle, there are probably better options now and may want to design something that is cross platform and can be easily used for different goals. 

Steven

> On Apr 30, 2021, at 8:56 AM, Davide Italiano <ditaliano at apple.com> wrote:
> 
> + Wu
> 
>> On Apr 30, 2021, at 8:10 AM, pawel k. <pawel.kunio at gmail.com <mailto:pawel.kunio at gmail.com>> wrote:
>> 
>> Hello,
>> Silly question but is xml the best format to be used? If so if it is fairly eparate lib, i could try to help with rewriting it.
>> 
>> Best regards,
>> Pawel Kunio
>> 
>> pt., 30.04.2021, 15:23 użytkownik Jez via llvm-dev <llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>> napisał:
>> +Davide -- do you know who (if anyone) at Apple maintains this?
>> 
>> Jez
>> 
>> On Fri, Apr 30, 2021 at 12:09 AM David Blaikie <dblaikie at gmail.com <mailto:dblaikie at gmail.com>> wrote:
>> >
>> > Might want to CC any of the original authors from Apple - I expect
>> > they'd have some thoughts on this, maybe know something about the
>> > maintained-ness status of libxar, etc.
>> >
>> > If we do end up writing something of our own, I wonder if it has to be
>> > xar or whether there's something else we should entertain? (maybe the
>> > bitcode format could be reused/broadened/or the like)
>> >
>> > On Thu, Apr 29, 2021 at 7:51 PM Jez via llvm-dev
>> > <llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>> wrote:
>> > >
>> > > Hi,
>> > >
>> > > I want to float the idea of rewriting this external dependency as part
>> > > of LLVM. For context, Apple's `-bitcode_bundle` flag packages bitcode
>> > > within the `__LLVM` segment of the larger executable. The bitcode
>> > > files are packaged by serializing them into a XAR (XML Archive) file,
>> > > which then gets copied into `__LLVM`. llvm-objdump and LLD use libxar
>> > > to read and write these XARs.
>> > >
>> > > I think there are several good reasons for writing our own libxar:
>> > > 1. libxar's interface doesn't allow for *not* writing to disk (i.e. we
>> > > cannot write to an mmap'ed region), so it incurs unnecessary I/O
>> > > overhead
>> > > 2. It doesn't support Windows
>> > > 3. It exposes a rather primitive C interface (using raw ints to
>> > > indicate error status) that is out of place in LLVM's C++
>> > >
>> > > The goal would be to have both LLD and llvm-objdump use this
>> > > home-grown implementation of libxar, instead of the system one.
>> > >
>> > > One possibility is to contribute to the existing libxar, but I don't
>> > > know if it is really maintained; Apple releases open source tarball
>> > > drops every so often, and there's https://mackyle.github.io/xar/ <https://mackyle.github.io/xar/> which
>> > > appears to be a fork of the now-defunct http://xar.googlecode.com/ <http://xar.googlecode.com/>,
>> > > but even that hasn't seen a commit since 2014.
>> > >
>> > > I may have an undergrad who's eager to take this work on, but before
>> > > they embark down that path I wanted to run it by y'all. Let me know if
>> > > you have thoughts.
>> > >
>> > > Cheers,
>> > > Jez
>> > > _______________________________________________
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