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bug#62253: Fakechroot execution engine doesn’t outlive ‘exec’ calls
From: |
Ludovic Courtès |
Subject: |
bug#62253: Fakechroot execution engine doesn’t outlive ‘exec’ calls |
Date: |
Sat, 18 Mar 2023 12:48:32 +0100 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/28.2 (gnu/linux) |
For ‘guix pack -RR’ packs, unlike the “userns” and “proot” execution
engines, the “fakechroot” execution engine doesn’t survive ‘exec’ calls:
--8<---------------cut here---------------start------------->8---
$ mkdir -p /tmp/fakechroot-test && cd /tmp/fakechroot-test/ && tar xf $(guix
pack -RR openmpi intel-mpi-benchmarks bash-minimal -S /bin=bin)
$ unshare -m -U -r -f sh -c 'mount -t tmpfs none /gnu;
GUIX_EXECUTION_ENGINE=fakechroot /tmp/fakechroot-test/bin/bash'
bash-5.1# echo /gnu/store/*coreutils*/bin/ls
/gnu/store/d251rfgc9nm2clzffzhgiipdvfvzkvwi-coreutils-8.32/bin/ls
/gnu/store/vqdsrvs9jbn0ix2a58s99jwkh74124y5-coreutils-minimal-8.32/bin/ls
bash-5.1# test -f /gnu/store/*coreutils-8*/bin/ls
bash-5.1# echo $?
0
bash-5.1# /gnu/store/*coreutils-8*/bin/ls
bash: /gnu/store/d251rfgc9nm2clzffzhgiipdvfvzkvwi-coreutils-8.32/bin/ls: No
such file or directory
--8<---------------cut here---------------end--------------->8---
This is because the ELF interpreter of the unwrapped ‘ls’ binary remains
/gnu/store/…-glibc-2.33/lib/ld-linux-x86-64-so.2 and no LD_PRELOAD
interposition can address that.
In this case, adding ‘coreutils’ to the profile (on the ‘guix pack’
command line) would give us wrapped binaries, and the problem is solved.
But in other cases, it’s not that simple. For instance, libmpi.so from
Open MPI tries to exec one its programs, using its absolute file name:
--8<---------------cut here---------------start------------->8---
$ unshare -m -U -r -f sh -c 'mount -t tmpfs none /gnu;
GUIX_EXECUTION_ENGINE=fakechroot /tmp/fakechroot-test/bin/IMB-MPI1'
--------------------------------------------------------------------------
The singleton application was not able to find the executable "orted" in
your PATH or in the directory where Open MPI/OpenRTE was initially installed,
and therefore cannot continue.
For reference, we tried the following command:
/gnu/store/c7g9qalmbz4a94hwzk1v1cbq7n5m8plq-openmpi-4.1.4/bin/orted
and got the error No such file or directory.
[…]
--8<---------------cut here---------------end--------------->8---
I can think of several ways to address that:
1. Change the exec* wrappers in libfakechroot such that, on ENOENT,
they try a direct ld.so invocation to run program, like
‘run-in-namespace.c’ does.
Problem is that for this to work correctly, it would need to
compute the ‘--library-path’ argument at run time, by computing the
equivalent of (map dirname (file-needed/recursive program)).
Impractical at best.
2. Wrap/graft every package in the closure (as opposed to generating
wrappers for just those packages that appear in the profile, which
is what ‘guix pack’ currently does).
The downside is that the “userns” and “proot” execution engines
don’t need something this heavyweight: they just need a leaf
package to be wrapped.
3. Ignore the problem. After all, we’re talking about a corner case
of the “fakechroot” engine, which is a niche within a niche.
Food for thought…
Ludo’.
- bug#62253: Fakechroot execution engine doesn’t outlive ‘exec’ calls,
Ludovic Courtès <=