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

[Steve McIntyre]

On Thu, Aug 11, 2016 at 12:28:47PM +0200, Ximin Luo wrote:
>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

Ugh. *None* of the Linux distros doing ARMv7 hard-float assume
NEON. The spec was agreed across the distros to explicitly *not*
depend on NEON for these ports because it's optional and there
are/were a number of ARMv7 CPUs in the wild without it. This appears
to be utterly broken behaviour by rust upstream.

-- 
Steve McIntyre, Cambridge, UK.                                steve at einval.com
"I've only once written 'SQL is my bitch' in a comment. But that code 
 is in use on a military site..." -- Simon Booth