--- Begin Message ---
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Subject: |
“fakechroot” execution engine doesn’t work for Bash |
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Date: |
Thu, 24 Mar 2022 22:02:00 +0100 |
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User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/27.2 (gnu/linux) |
Hello!
The “fakechroot” engine fails when applied to ‘bash’:
--8<---------------cut here---------------start------------->8---
$ guix pack -RR bash -S /bin=bin
/gnu/store/mnbmklbvd1pk7yby0k8h26msk6z11m1m-bash-tarball-pack.tar.gz
$ (cd /tmp/pack; tar xf
/gnu/store/mnbmklbvd1pk7yby0k8h26msk6z11m1m-bash-tarball-pack.tar.gz)
$ unshare -mrf sh -c 'mount -t tmpfs -o ro none /gnu/store;
GUIX_EXECUTION_ENGINE=fakechroot /tmp/pack/bin/bash --version'
/tmp/pack/gnu/store/d99ykvj3axzzidygsmdmzxah4lvxd6hw-bash-5.1.8/bin//bash: out
of memory to store relocation results for /tmp/pack/bin/bash
--8<---------------cut here---------------end--------------->8---
The message comes from ld.so. My guess is that the problem comes from
Bash’s terrible ‘malloc’ replacement:
--8<---------------cut here---------------start------------->8---
$ objdump -T /gnu/store/d99ykvj3axzzidygsmdmzxah4lvxd6hw-bash-5.1.8/bin/bash |
grep malloc
00000000004ae6f0 g DF .text 000000000000003b Base malloc_usable_size
00000000004ae850 g DF .text 0000000000000009 Base malloc
0000000000484e70 g DF .text 000000000000005b Base xmalloc
00000000004ee020 g DO .bss 0000000000000004 Base
malloc_trace_at_exit
00000000004e8c24 g DO .data 0000000000000004 Base
malloc_mmap_threshold
0000000000484f70 g DF .text 00000000000000dd Base sh_xmalloc
00000000004f7a04 g DO .bss 0000000000000004 Base malloc_trace
00000000004f7a08 g DO .bss 0000000000000004 Base malloc_flags
00000000004ae730 g DF .text 0000000000000005 Base sh_malloc
00000000004f7a00 g DO .bss 0000000000000004 Base malloc_register
00000000004ae660 g DF .text 000000000000000c Base
_malloc_unblock_signals
00000000004ae630 g DF .text 000000000000002e Base
_malloc_block_signals
--8<---------------cut here---------------end--------------->8---
[Time passes…] I confirmed this hypothesis by running:
guix pack -RR -S /bin=bin -m manifest.scm
on this manifest:
--8<---------------cut here---------------start------------->8---
(use-modules (guix) (guix utils)
(guix profiles)
(gnu packages bash))
(define bash-sans-malloc
(package/inherit bash
(name "bash-sans-malloc")
(arguments
(substitute-keyword-arguments (package-arguments bash)
((#:configure-flags flags ''())
`(cons "--without-bash-malloc" ,flags))))))
(packages->manifest (list bash-sans-malloc))
--8<---------------cut here---------------end--------------->8---
Works just fine:
--8<---------------cut here---------------start------------->8---
$ unshare -mrf sh -c 'mount -t tmpfs -o ro none /gnu/store;
GUIX_EXECUTION_ENGINE=fakechroot /tmp/pack/bin/bash --version'
GNU bash, version 5.1.8(1)-release (x86_64-unknown-linux-gnu)
Copyright (C) 2020 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software; you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
--8<---------------cut here---------------end--------------->8---
So in the end, it’s a bug report that’s kinda closed already.
Perhaps we should build Bash ‘--without-bash-malloc’ unconditionally in
‘core-updates’? The ‘INSTALL’ file reads:
--8<---------------cut here---------------start------------->8---
'--with-bash-malloc'
Use the Bash version of 'malloc' in the directory 'lib/malloc'.
This is not the same 'malloc' that appears in GNU libc, but an
older version originally derived from the 4.2 BSD 'malloc'. This
'malloc' is very fast, but wastes some space on each allocation.
This option is enabled by default. The 'NOTES' file contains a
list of systems for which this should be turned off, and
'configure' disables this option automatically for a number of
systems.
--8<---------------cut here---------------end--------------->8---
There might be other options if we want to keep it, such as changing the
ELF visibility of those symbols, but I wonder if it’s worth the effort.
Thoughts?
Ludo’.
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--- Begin Message ---
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Subject: |
Re: bug#54557: “fakechroot” execution engine doesn’t work for Bash |
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Date: |
Mon, 28 Mar 2022 12:06:20 +0200 |
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User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/27.2 (gnu/linux) |
Hi,
Maxim Cournoyer <maxim.cournoyer@gmail.com> skribis:
> I'd be OK with --without-bash-malloc; it seems we'll pay a bit in terms
> of Bash performance in exchange for better memory usage. It also brings
> benefits such as solving this issue and may benefit from
> advances/bugfixes to glibc's malloc in the future, if there are any.
We might actually benefit from the improvements made in glibc’s malloc
over the years (it’s more actively developed than that of Bash), who
knows.
Anyway, pushed to ‘core-updates’ as
c6b5161e97ed1010d61331874b09c3231af3b1f9.
Thanks,
Ludo’.
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