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Segfault in MIPS codegen at -O3 #371
Description
Trying to build https://github.com/johnsonjh/lzpack. There are actually a few different LZPACK build configurations possible, but the "simplest" is the in-memory compressor.
Build stubs (using host tooling):
git clone https://github.com/johnsonjh/lzpack.git
cd lzpack
make stubsBuilding LZPACK for MIPS with no optimization (same with -O, -O1, and -O2):
/opt/ack/bin/ack -D__ACK__ -mlinuxmips -o lzpack lzpack.c
"ack.ack-7b528104.so", line 2784: relocation offset in ha16[] too big (fatal)Building LZPACK for MIPS with -O3 optimization:
/opt/ack/bin/ack -D__ACK__ -mlinuxmips -O3 -o lzpack lzpack.c
/opt/ack/bin/ack: /opt/ack/lib/ack/linuxmips/mcg died with signal 11
[2183551.901479] mcg[3191164]: segfault at 10 ip 00000000004018ff sp 00007ffd63b0dd80 error 4 in mcg[18ff,400000+13000] likely on CPU 2 (core 2, socket 0)
[2183551.901494] Code: 4c 89 ee e8 6e ff 00 00 48 85 c0 75 15 49 8d bc 24 88 00 00 00 4c 89 ee e8 59 ff 00 00 48 85 c0 74 15 48 8b 40 08 48 63 53 04 <48> 8b 40 10 48 8b 34 d0 e9 91 00 00 00 8b 53 04 41 8b 75 00 bf dfThe Linux/386, Linux/m68k, and Linux/PPC targets all build LZPACK (and it works correctly).
Activity
johnsonjh commentedon Jul 16, 2026
The "streaming" version of LZPACK does build ...
... but it doesn't actually work:
ERROR: cannot create temp file LZTMP.$$$johnsonjh commentedon Jul 16, 2026
The streaming issue is wrong flags used, I did a quick fix for that but got some other issues. I'll see what I can do.
johnsonjh commentedon Jul 16, 2026
I actually have some fixes for these issues (along with a workaround in LZPACK itself for one issue I couldn't figure out) which allow LZPACK to build and work with the streaming compressor (any optimization level too), and the full compressor but only without optimization. Using -O3 still fails.
I'll get the changes into LZPACK and create a PR once I clean it up. It will be a bit better still but by no means perfect. If you have any questions about the changes let me know.
johnsonjh commentedon Jul 16, 2026
#372 fixes (most of these issues).
The workaround for a remaining bug in the mcg optimizer is going into the LZPACK repo as soon as my local CI finishes there.
Unfortunately, I've reached the limits of my skills with this I think, unless I can find a lot more time to sink into it.