Thanks Thomas to reassign so I finally got aware of this.

At least I can confirm the issue on Xenial:
qemu at version 1:2.5+dfsg-5ubuntu10.6

sudo qemu-debootstrap --no-check-gpg --arch=sparc64 sid sparc64 http://ftp.debian-ports.org/debian
[...]
I: Running command: chroot sparc64 /debootstrap/debootstrap --second-stage
Unhandled trap: 0x34
pc: 0000000000110688  npc: 000000000011068c
%g0-3: 0000000000000000 0000000000000001 0000000000218c00 0000000000000000
%g4-7: 0000000000000000 00000000009e3440 00000000000000b1 000000400092a400
%o0-3: 0000000000000014 00000040007ff8e9 00000040007ff8e9 0000000000000000 
%o4-7: 0000000000000000 0000000000000000 00000040007ff829 00000040007ff991 
%l0-3: 0000000000000000 0000000000000000 0000000000000000 0000004000801f00 
%l4-7: 0000000000000000 0000000000000020 0000004000b8f5c8 0000004000b8e000 
%i0-3: 0000000000000001 000000000021e800 000000000021b400 0000000000219000 
%i4-7: 0000000000218800 000000000021b770 00000040007ffdc1 000000000010af14 
%f00:  636865636b696e67 202061766f696420 2020202020207363 7261746368626f78
%f08:  202061766f696420 65290a2020202020 20812d812d6b6579 72696e67813d4b20
%f16:  7573652076617269 616e742058206f66 2074686520626f6f 7473747261702073
%f24:  6372697074730a20 2020202020202020 2020202020202020 2020202020202020
%f32:  2020202028637572 72656e746c792073 7570706f72746564 2076617269616e74
%f40:  73813a206275696c 64642c2066616b65 6368726f6f742c0a 2020202020202020
%f48:  20812d812d6b6579 2020202020202020 2020202020202020 2020202020202020
%f56:  2020202020207363 7261746368626f78 2c206d696e626173 65290a2020202020
pstate: 00000092 ccr: 44 (icc: -Z-- xcc: -Z--) asi: f0 tl: 0 pil: 0
cansave: 3 canrestore: 3 otherwin: 0 wstate: 0 cleanwin: 7 cwp: 5
fsr: 0000000000000000 y: 0000000000000000 fprs: 0000000000000004


Similar for Yakkety:
qemu version 1:2.6.1+dfsg-0ubuntu9

I: Running command: chroot sparc64 /debootstrap/debootstrap --second-stage
Unhandled trap: 0x34
pc: 0000000000110688  npc: 000000000011068c
%g0-3: 0000000000000000 0000000000000001 0000000000218c00 0000000000000000
%g4-7: 0000000000000000 00000000009e3440 0000000000000214 000000400092a400
%o0-3: 0000000000000014 00000040007ffa59 00000040007ffa59 0000000000000000 
%o4-7: 0000000000000000 0000000000000000 00000040007ff999 00000040007ffb01 
%l0-3: 0000000000000000 0000000000000000 0000000000000000 0000004000801f44 
%l4-7: 0000000000000000 0000000000000020 0000004000b8f5c8 0000004000b8e000 
%i0-3: 0000000000000001 0000000000249260 000000000021b400 0000000000219000 
%i4-7: 0000000000218800 000000000021b770 00000040007fff31 000000000010af14 
%f00:  636865636b696e67 202061766f696420 20812d812d6b6579 72696e67813d4b20
%f08:  202061766f696420 202020636865636b 2052656c65617365 2066696c65732061
%f16:  6372697074730a20 2020202020202020 2020202020202020 2020202020202020
%f24:  2020202028637572 72656e746c792073 7570706f72746564 2076617269616e74
%f32:  73813a206275696c 64642c2066616b65 6368726f6f742c0a 2020202020202020
%f40:  2020202020202020 2020202020202020 2020202020207363 7261746368626f78
%f48:  2052656c65617365 2020202020202020 2020202020207363 7261746368626f78
%f56:  2c206d696e626173 65290a2020202020 20812d812d6b6579 72696e67813d4b20
pstate: 00000092 ccr: 44 (icc: -Z-- xcc: -Z--) asi: f0 tl: 0 pil: 0
cansave: 3 canrestore: 3 otherwin: 0 wstate: 0 cleanwin: 7 cwp: 5
fsr: 0000000000000000 y: 0000000000000000 fprs: 0000000000000004