lrzip dies on ppc64el when using zpaq

I found that this is size dependent, but not in the gigabytes.
This is the first that fails:
$ rm file.lrz; dd if=/dev/zero of=file bs=1 count=64; lrzip -z file
While this still works
$ rm file.lrz; dd if=/dev/zero of=file bs=1 count=63; lrzip -z file

Thread 3 "lrzip" received signal SIGILL, Illegal instruction.
[Switching to Thread 0x3fffb312f180 (LWP 130922)]
0x00003fffb7f70000 in ?? ()
(gdb) bt
#0 0x00003fffb7f70000 in ?? ()
#1 0x00000000100363f8 in libzpaq::Predictor::predict (this=0x3fffb3113430) at libzpaq/libzpaq.cpp:3140
#2 0x000000001003792c in libzpaq::Encoder::compress (this=0x3fffb3113420, c=<optimized out>)
    at libzpaq/libzpaq.cpp:1409
#3 0x0000000010037c9c in libzpaq::Compressor::postProcess (this=0x3fffb3113360, pcomp=0x0, len=<optimized out>)
    at libzpaq/libzpaq.cpp:1548
#4 0x000000001003826c in libzpaq::compress (in=0x3fffb312e508, out=0x3fffb312e4f0, level=<optimized out>)
    at libzpaq/libzpaq.cpp:1597
#5 0x0000000010038424 in zpaq_compress (c_buf=0x3fffac0008c0 "zPQ\001\001E", c_len=0x3fffb312e708,
    s_buf=0x100a3270 "", s_len=<optimized out>, level=<optimized out>, msgout=<optimized out>,
    progress=<optimized out>, thread=<optimized out>) at libzpaq/libzpaq.h:526
#6 0x0000000010014a98 in zpaq_compress_buf (thread=<optimized out>, cthread=0x10092a68,
    control=0x10070c50 <local_control>) at stream.c:184
#7 compthread (data=0x0) at stream.c:1296
#8 0x00003fffb7e58070 in start_thread (arg=0x3fffb312f180) at pthread_create.c:335
#9 0x00003fffb7a73230 in clone () at ../sysdeps/unix/sysv/linux/powerpc/powerpc64/clone.S:96

They really do JIT in there with a "A ZPAQL virtual machine"

Found in the code:
const int S=sizeof(char*); // 4 = x86, 8 = x86-64
if (*(char*)&t!=0x78 || (S!=4 && S!=8))
    error("JIT supported only for x86-32 and x86-64");

Yet the arch check code is not strong, it lets ppc through and then fails.
It also seems to have "invalid instruction" code detection but that only works on x86 as well.

TL;DR Jit in zpac isn't good for non x86.

Here from the header libzpaq/libzpaq.h

By default, LIBZPAQ uses JIT (just in time) acceleration. This only
works on x86-32 and x86-64 processors that support the SSE2 instruction
set. To disable JIT, compile with -DNOJIT. To enable run time checks,
compile with -DDEBUG. Both options will decrease speed.

Even guaranteeing SSE2 is not sure on old machines or some virtual machines.
Usually runtime detection has to be used on those.

I think the only real "safe" option is to build with -DNOJIT on all architectures.

Hmm a simple override of this did not pass down.
So the following did not help.

diff -Nru lrzip-0.631/debian/changelog lrzip-0.631/debian/changelog
--- lrzip-0.631/debian/changelog 2016-11-14 01:20:43.000000000 +0100
+++ lrzip-0.631/debian/changelog 2017-03-02 09:40:03.000000000 +0100
@@ -1,3 +1,9 @@
+lrzip (0.631-1ubuntu1~ppa2) xenial; urgency=medium
+
+ * Experimental build for ppc to check JIT disabling
+
+ -- Christian Ehrhardt <email address hidden> Thu, 02 Mar 2017 09:35:06 +0100
+
 lrzip (0.631-1) unstable; urgency=low

   * New upstream release.
diff -Nru lrzip-0.631/debian/rules lrzip-0.631/debian/rules
--- lrzip-0.631/debian/rules 2014-03-28 19:08:25.000000000 +0100
+++ lrzip-0.631/debian/rules 2017-03-02 09:35:02.000000000 +0100
@@ -12,6 +12,10 @@
 CFLAGS += -Wall -pedantic
 LDFLAGS += -Wl,--as-needed

+# Disable Jit as it is x86 >=sse2 only which can not be guaranteed
+# https://bugs.launchpad.net/cloud-images/+bug/1668876
+CFLAGS += -DNOJIT
+
 override_dh_auto_configure:
        # With pristine tarballs from version control, there is no ./configure
        [ -f configure ] || autoreconf -vfi

It seems https://launchpadlibrarian.net/309385381/buildlog_ubuntu-xenial-ppc64el.lrzip_0.631-1ubuntu1~ppa2_BUILDING.txt.gz that the build of libzpaq/ completely ignores the extra CFLAGS

Well that is CPP

This is working now just fine:
--- lrzip-0.631/debian/rules 2014-03-28 19:08:25.000000000 +0100
+++ lrzip-0.631/debian/rules 2017-03-02 10:23:30.000000000 +0100
@@ -10,8 +10,13 @@

 include /usr/share/dpkg/buildflags.mk
 CFLAGS += -Wall -pedantic
+CXXFLAGS += -Wall -pedantic
 LDFLAGS += -Wl,--as-needed

+# Disable Jit as it is x86 >=sse2 only which can not be guaranteed
+# https://bugs.launchpad.net/cloud-images/+bug/1668876
+CXXFLAGS += -DNOJIT
+

I reported a fix to Debian, linking as soon as I have a bug #.