Re: [MirageOS-devel] Some issues building mirage with virtio

[Hannes Mehnert <hannes@xxxxxxxxxxx>]

Dear Nick,

On 18/05/2018 20:21, Nicholas Robison wrote:
> I’ve been working on a small project to port my personal website over to a 
> Mirage Unikernel. So far, it’s been a lot of fun and the project continues to 
> amaze me!


great to hear this!


> My app is largely a fork of the mirage-www project, with a few tweaks. While 
> I’ve been able to get everything working under MacOS and Unix, I’m having 
> some issues building the final image for deployment on GCE using virtio. 
> 
> Using Travis under Ubuntu 14.04, I’m getting the following build error, which 
> shows up regardless of what OCaml version I use (tested on 4.04.2 through 
> 4.06.1). I can also replicate the issue on an Ubuntu 16.04 local VM.
> 
> ocamlfind ocamlopt -g -dontlink unix -dontlink str -dontlink num -dontlink 
> threads -linkpkg -output-obj -package tcpip.udp -package tcpip.tcp -package 
> tcpip.stack-direct -package tcpip.icmpv4 -package tcpip.ethif -package 
> tcpip.arpv4 -package tcpip -package sexplib -package re -package ptime 
> -package nocrypto.mirage -package nocrypto -package mirage-types-lwt -package 
> mirage-types -package mirage-solo5 -package mirage-runtime -package 
> mirage-random -package mirage-net-solo5 -package mirage-logs -package 
> mirage-conduit -package mirage-clock-freestanding -package 
> mirage-bootvar-solo5 -package lwt -package io-page -package functoria-runtime 
> -package ezjsonm -package duration -package cowabloga -package cow -package 
> core_kernel -package cohttp-mirage -package charrua-client-mirage -package 
> astring -predicates mirage_solo5 site_config.cmx pages.cmx blog.cmx data.cmx 
> key_gen.cmx dispatch.cmx static1.cmx static2.cmx main.cmx -o main.native.o
>  <>_build/main.native.o: In function `camlBase__Import0__entry':
>  
> <>/home/travis/.opam/4.06.1/build/base.v0.10.0/_build/default/src/import0.ml:249:
>  undefined reference to `Base_am_testing'
> [...]
> It seems related to using the Base library, which I pulled via
core_kernel for a couple of list functions that I need. When running
‘make depends’ I can see the following output, which shows that base is
being downgraded, but only to the prior release, so seems odd it would
be missing symbols. Unless I’m miss-reading the error?

The issue originates from your linker when linking the static binary
(virtual machine image) - it complains that some symbols are missing.
The underlying issue is that the base library uses some functions
implemented in C which do not work on MirageOS (which does (a) run in
ring0, and thus C code needs to be compiled with -no-red-zone and other
flags and (b) does not include a full C library, only a tiny set of
symbols required for the OCaml runtime (such as memcmp, memcpy,
memmove).  It works with the Unix target since there the libc is available.

If you avoid using Base and Core_kernel (and instead use the OCaml
stdlib), your website will work with virtio.  If you need some help,
please let us know and provide a link to your repository.


Have a nice day,

hannes

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