[Pkg-rust-maintainers] Bug#834003: rustc: armhf FTBFS because upstream assumes armhf has neon but debian does not

[Ximin Luo]

Package: rustc
Version: 1.10.0+dfsg1-2
Severity: normal

Dear Maintainer,

armhf currently fails to build on buildds but does build successfully on
porterbox harris.debian.org

This is because rust upstream assumes arm-unknown-linux-gnueabi has neon:

src/librustc_back/target/armv7_unknown_linux_gnueabihf.rs:            features: "+v7,+vfp3,+neon".to_string(),

whereas Debian's armhf targets machines without neon, including all current
buildds, but only harris has it:

infinity0 at harris:~$ grep neon /proc/cpuinfo 
Features	: swp half thumb fastmult vfp edsp thumbee neon vfpv3 tls vfpd32 

The build fails running the upstream stage0 compiler because that contains
neon instructions. To fix this we'll have to

1) patch rustc to not use neon, and
2) do a binary-only upload for armhf, either by
   a) building on harris, but this takes 2-3 days
   b) finding a faster armhf machine with neon to build it on, or
   b) cross-compiling from another architecture

X

-- System Information:
Debian Release: stretch/sid
  APT prefers testing
  APT policy: (990, 'testing'), (500, 'stable'), (300, 'unstable'), (200, 'experimental')
Architecture: amd64 (x86_64)
Foreign Architectures: i386

Kernel: Linux 4.6.0-1-amd64 (SMP w/4 CPU cores)
Locale: LANG=en_GB.utf8, LC_CTYPE=en_GB.utf8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)

Versions of packages rustc depends on:
ii  gcc                   4:5.3.1-3
ii  libc6                 2.23-4
ii  libc6-dev [libc-dev]  2.23-4
ii  libjs-jquery          1.12.4-1
ii  libstd-rust-dev       1.12.0~~nightly.20160805+dfsg1-1

Versions of packages rustc recommends:
ii  rust-gdb  1.10.0+dfsg1-1

Versions of packages rustc suggests:
ii  rust-doc  1.10.0+dfsg1-1

-- no debconf information