Cross building ports amd64/armv6

[Chris Rees]

Hi all,

Got a weird problem (as you'd expect with cross-built ports!)

I have a cross-building toolchain made with [1] (irrelevant to this 
issue), and I'm using poudriere to build ports for my R-Pi.

It's mainly working great, save a few issues with ld for which I'm 
disabling the cross-building tools and using the native ones.  The issue 
I have is with the odd port that tries to install(1) empty files, such 
as lang/python27 and audio/libvorbis [2].

I can reproduce this by entering the build jail, and *on the wrkdir 
mount* touching a, installing a b.

The wrkdir is created with mdconfig -a -t swap -s 3G by poudriere, and 
it doesn't happen on the zfs partition that the partition resides on.  
I've narrowed it down to this ancient optimisation (mmap and write if 
less than 8M), which is from ~r1000 [3]; if I disable this block of code 
and just use the code below it (read to buf, write from buf) the problem 
disappears.

Firstly, is this known?  Secondly, is it likely to be possible/a 
priority to fix?  It could be anything, but my suspicion is that it's an 
endian issue, as somehow nw ends up negative (error from line 1181).  I 
could be wrong.  Could also somehow be a 64/32bit issue... I'll stop 
guessing.

Does anyone have any ideas please?

[crees at pegasus]~% uname -a
FreeBSD pegasus.bayofrum.net 10.2-RELEASE-p2 FreeBSD 10.2-RELEASE-p2 #2 
r287474: Sat Sep  5 17:56:09 BST 2015 
root at pegasus.bayofrum.net:/usr/obj/usr/src/sys/PEGASUS  amd64

Chris

[1] 
http://phaq.phunsites.net/2015/10/11/freebsd-on-armv6-cross-compile-performance-optimization-for-poudriere/

[2] 
https://www.bayofrum.net/pkg/102armv6-default/2015-12-27_22h07m30s/logs/errors/libvorbis-1.3.5,3.log

[3] 
http://svnweb.freebsd.org/base/head/usr.bin/xinstall/xinstall.c?revision=291091&view=markup#l1168

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