Debian sparc64 works on hardware, segfaults in qemu
Description of problem:

Steps to reproduce:
1. Start the installer normally (boot cdrom), use guided all disk partition, change ext4 to btrfs for /
2. Installer always segfaults at the same place while installing base system step:

```
Jan 28 09:17:48 debootstrap: Setting up mawk (1.3.4.20200120-3.1) ...
Jan 28 09:17:49 debootstrap: update-alternatives:
Jan 28 09:17:49 debootstrap: using /usr/bin/mawk to provide /usr/bin/awk (awk) i
n auto mode
Jan 28 09:17:49 debootstrap:
Jan 28 09:17:54 debootstrap: Selecting previously unselected package debconf.
Jan 28 09:17:54 debootstrap: (Reading database ... 1459 files and directories cu
rrently installed.)
Jan 28 09:17:54 debootstrap: Preparing to unpack .../debconf_1.5.82_all.deb ...
Jan 28 09:17:54 debootstrap: Unpacking debconf (1.5.82) ...
Jan 28 09:17:55 kernel: [ 2994.426867] dpkg-deb[12709]: segfault at ffffffffffff
ffff ip fffff80100a1c3ec (rpc 0000000000000030) sp fffff80102402041 error 1 in l
iblzma.so.5.4.1[fffff80100a00000+2a000]
Jan 28 09:17:55 debootstrap: dpkg-deb: error: <decompress> subprocess was killed
 by signal (Segmentation fault)
Jan 28 09:17:56 debootstrap: dpkg: error processing archive /var/cache/apt/archi
ves/debconf_1.5.82_all.deb (--install):
Jan 28 09:17:56 debootstrap:  dpkg-deb --fsys-tarfile subprocess returned error
exit status 2
Jan 28 09:17:57 debootstrap: Errors were encountered while processing:
Jan 28 09:17:57 debootstrap:  /var/cache/apt/archives/debconf_1.5.82_all.deb
Jan 28 09:18:10 base-installer: error: exiting on error base-installer/debootstr


cd /target/var/cache/apt/archives
# ar x debconf_1.5.82_all.deb
/target/var/cache/apt/archives # unxz data.tar.xz
/target/var/cache/apt/archives # unxz control.tar.xz
```
another try, to ext2 fs:
```
Jan 28 10:31:16 debootstrap: Preparing to unpack .../dpkg_1.21.21_sparc64.deb ..
.
Jan 28 10:31:16 debootstrap: Unpacking dpkg (1.21.21) over (1.21.21) ...
Jan 28 10:31:23 kernel: [ 7402.528016] dpkg-deb[20720]: segfault at 7240015 ip f
ffff8010091def4 (rpc 000000006e17c498) sp fffff80103124041 error 1 in liblzma.so
.5.4.1[fffff80100900000+2a000]
Jan 28 10:31:23 debootstrap: dpkg-deb: error: <decompress> subprocess was killed
 by signal (Segmentation fault)
Jan 28 10:31:24 debootstrap: dpkg: error processing archive /var/cache/apt/archi
ves/dpkg_1.21.21_sparc64.deb (--install):
Jan 28 10:31:24 debootstrap:  cannot copy extracted data for './usr/share/doc/dp
kg/changelog.gz' to '/usr/share/doc/dpkg/changelog.gz.dpkg-new': unexpected end
of file or stream
```
Additional information:
All times i've tried under Ubuntu qemu or latest build for Windows it segfaults unpacking package, and i believe it's a misleading error message, since very same ISO installs normally on Sun Fire T1000 machine (sun4v). I've tried also booting FreeBSD-12.4-RELEASE-sparc64-disc1.iso which dies shortly after booting the kernel, but i am more interested in Debian, since it was verified to work on a real hardware. BTW i was able to unpack specified file with "ar x" within installer.