[llvm-dev] Porting libxar to LLVM

[Davide Italiano via llvm-dev]

+ Wu

> On Apr 30, 2021, at 8:10 AM, pawel k. <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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