On Sun, 07 Sep 2014 at 13:58:40 +0200, Marc Kleine-Budde wrote:
> BTW: even "lzop" fails with the new liblzo library:
>
> $ lzop
> Lempel-Ziv-Oberhumer Packer
> Copyright (C) 1996 - 2010
> lzop v1.03 Markus Franz Xaver Johannes Oberhumer Nov
> 1st 2010
>
> lzo_init() failed - check your LZO installation !
This bit me on a recently-upgraded jessie system where I'm somewhat
reliant on openvpn, so after working around it by downgrading liblzo2-2
to the wheezy-security version, I looked further into it.
You don't actually need to build packages at all: the same failure occurs
in a freshly compiled lzo2 tree (just ./configure && make) using
"LD_LIBRARY_PATH=src/.libs gdb lzop", "run".
When rebuilt with CFLAGS="-O0 -g" it works. So, some optimization is
to blame for this.
When rebuilt with CFLAGS="-Og -g" it fails, and this time it's possible
to see *where* it fails, because the assignment to r isn't optimized out:
(gdb) break _lzo_config_check
...
_lzo_config_check () at src/lzo_init.c:100
(gdb) watch r
(gdb) s
...
_lzo_config_check () at src/lzo_init.c:117
117 r &= UA_GET_NE16(p) == 0;
(gdb)
lzo_memops_get_ne16 (ss=0xbefff1f1) at src/lzo_func.h:387
387 LZO_MEMOPS_COPY2(&v, ss);
(gdb)
Watchpoint 4: r
Old value = 1
New value = 0
My next try was CPPFLAGS="-DLZO_CFG_NO_UNALIGNED" to stop lzo doing
"clever" pointer dereferences in LZO_MEMOPS_COPY2, and sure enough,
that works. So we have a workaround: define that macro on at least armel.
It might slow lzo2 down, but working slowly is better than failing rapidly.
(My next idea was -fno-strict-aliasing, but unfortunately that didn't work.)
This optimization stuff made me suspicious about new compiler optimizations
since wheezy's (working) lzo2 was compiled. It's getting late now, but the
next thing I try is going to be rebuilding wheezy's lzo2 on a jessie system
to see whether it has the same failure conditions.
I'd really like to see this fixed in jessie; I'm tempted to say it
should be RC. I'll try to produce and test a complete patch, either
using CPPFLAGS="-DLZO_CFG_NO_UNALIGNED" on armel or preferably turning off
some specific optimization.
Hope this helps,
S
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