bug#26976: On Hydra, offload crashes while trying to build linux-libre source

[Ludovic Courtès]

Hi again,

I was able to reproduce it on hydra.gnu.org with:

  guix copy --to=hydra.gnunet.org 
/gnu/store/gi7r1v65zqhh8riqprq8nchfc9v9k156-guix-current

which leads most of the time to SIGSEGV (I couldn’t get the SIGSEGV on
my laptop):

--8<---------------cut here---------------start------------->8---
Thread 1 received signal SIGSEGV, Segmentation fault.
0x00007f121ff61ac7 in deflate_fast () from 
/gnu/store/jwkcd7siv6fcyl0qsg607bg9c8ap0gqr-zlib-1.2.11/lib/libz.so.1
(gdb) bt
#0  0x00007f121ff61ac7 in deflate_fast () from 
/gnu/store/jwkcd7siv6fcyl0qsg607bg9c8ap0gqr-zlib-1.2.11/lib/libz.so.1
#1  0x00007f121ff6378d in deflate () from 
/gnu/store/jwkcd7siv6fcyl0qsg607bg9c8ap0gqr-zlib-1.2.11/lib/libz.so.1
#2  0x00007f121e281451 in gzip_compress () from 
/gnu/store/vlc43y485v80sgq7iw60hzy4pw5r52d2-libssh-0.7.4/lib/libssh.so.4
#3  0x00007f121e281783 in compress_buffer () from 
/gnu/store/vlc43y485v80sgq7iw60hzy4pw5r52d2-libssh-0.7.4/lib/libssh.so.4
#4  0x00007f121e266ea7 in packet_send2 () from 
/gnu/store/vlc43y485v80sgq7iw60hzy4pw5r52d2-libssh-0.7.4/lib/libssh.so.4
#5  0x00007f121e257598 in channel_write_common () from 
/gnu/store/vlc43y485v80sgq7iw60hzy4pw5r52d2-libssh-0.7.4/lib/libssh.so.4
#6  0x00007f121e6c15ee in write_to_channel_port () from 
/gnu/store/ql5h9hxh5560d42xdirh0yxzrgii6i0m-guile-ssh-0.11.0/lib/libguile-ssh.so.11
#7  0x00007f122532472c in scm_i_write_bytes () from 
/gnu/store/5zx29y44nrqj0s8h3jlvlj82k8hj4dxs-guile-2.2.2/lib/libguile-2.2.so.1
#8  0x00007f122532bde4 in scm_put_bytevector () from 
/gnu/store/5zx29y44nrqj0s8h3jlvlj82k8hj4dxs-guile-2.2.2/lib/libguile-2.2.so.1
#9  0x00007f1225360c4d in vm_regular_engine () from 
/gnu/store/5zx29y44nrqj0s8h3jlvlj82k8hj4dxs-guile-2.2.2/lib/libguile-2.2.so.1
--8<---------------cut here---------------end--------------->8---

Unfortunately, when running under “valgrind --trace-children=yes”, it
doesn’t segfault and Valgrind doesn’t report anything interesting
(neither on hydra.gnu.org nor on my laptop).

I built libssh and guile-ssh with -fsanitize=address on my laptop but
that doesn’t report anything useful either.

Suggestions welcome!

Ludo’.