Illegal instruction when debootstrapping Debian

I'm trying to install a Debian chroot with debootstrap but the chroot
fails immediately with "Illegal instruction".

More specifically, I have a BT Homehub 5a with LEDE-17.01 uname -a
tells me it's running a mips kernel, so I did:

# opkg install debootstrap
# debootstrap --arch=mips stable /mnt/1/.

and after a while it fails with:

I: Extracting util-linux...
I: Extracting zlib1g...
W: Failure trying to run: chroot /mnt/1/. dpkg-deb -f /var/cache/apt/archives/dpkg_1.18.24_mips.deb Version
W: See /mnt/1/./debootstrap/debootstrap.log for details
W: Failure trying to run: chroot /mnt/1/. mount -t proc proc /proc
W: See /mnt/1/./debootstrap/debootstrap.log for details

consulting the log file I see:

# cat  /mnt/1/./debootstrap/debootstrap.log
Illegal instruction
Illegal instruction

and indeed

# chroot /mnt/1/. /bin/sh
Illegal instruction

Any idea what might be going on and what I might do to solve this problem?
How could I find out which "illegal instruction" it's trying to execute?

You probably need to patch the OpenWrt kernel to enable FPU emulation.