From: Peter Maydell <1805913@bugs.launchpad.net>
To: qemu-devel@nongnu.org
Subject: [Bug 1805913] Re: readdir() returns NULL (errno=EOVERFLOW) for 32-bit user-static qemu on 64-bit host
Date: Tue, 20 Apr 2021 09:16:32 -0000 [thread overview]
Message-ID: <161891019283.10217.14297973480552093714.malone@chaenomeles.canonical.com> (raw)
In-Reply-To: 154353638253.10384.17899256838547579767.malonedeb@chaenomeles.canonical.com
This is still a bug, and still blocked on the kernel providing APIs to QEMU to request 32-bit directory entries. Linus Walleij proposed a kernel patch to add a suitable fcntl flag but as far as I'm aware it didn't get in so far:
https://lore.kernel.org/qemu-devel/20201117233928.255671-1-linus.walleij@linaro.org/
** Changed in: qemu
Status: Incomplete => Confirmed
--
You received this bug notification because you are a member of qemu-
devel-ml, which is subscribed to QEMU.
https://bugs.launchpad.net/bugs/1805913
Title:
readdir() returns NULL (errno=EOVERFLOW) for 32-bit user-static qemu
on 64-bit host
Status in QEMU:
Confirmed
Bug description:
This can be simply reproduced by compiling and running the attached C
code (readdir-bug.c) under 32-bit user-static qemu, such as qemu-arm-
static:
# Setup docker for user-static binfmt
docker run --rm --privileged multiarch/qemu-user-static:register --reset
# Compile the code and run (readdir for / is fine, so create a new directory /test).
docker run -v /path/to/qemu-arm-static:/usr/bin/qemu-arm-static -v /path/to/readdir-bug.c:/tmp/readdir-bug.c -it --rm arm32v7/ubuntu:18.10 bash -c '{ apt update && apt install -y gcc; } >&/dev/null && mkdir -p /test && cd /test && gcc /tmp/readdir-bug.c && ./a.out'
dir=0xff5b4150
readdir(dir)=(nil)
errno=75: Value too large for defined data type
Do remember to replace the /path/to/qemu-arm-static and /path/to
/readdir-bug.c to the actual paths of the files.
The root cause is in glibc:
https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/unix/sysv/linux/getdents.c;h=6d09a5be7057e2792be9150d3a2c7b293cf6fc34;hb=a5275ba5378c9256d18e582572b4315e8edfcbfb#l87
By C standard, the return type of readdir() is DIR*, in which the
inode number and offset are 32-bit integers, therefore, glibc calls
getdents64() and check if the inode number and offset fits the 32-bit
range, and reports EOVERFLOW if not.
The problem here is for 32-bit user-static qemu running on 64-bit
host, getdents64 simply passing through the inode number and offset
from underlying getdents64 syscall (from 64-bit kernel), which is very
likely to not fit into 32-bit range. On real hardware, the 32-bit
kernel creates 32-bit inode numbers, therefore works properly.
The glibc code makes sense to do the check to be conformant with C
standard, therefore ideally it should be a fix on qemu side. I admit
this is difficult because qemu has to maintain a mapping between
underlying 64-bit inode numbers and 32-bit inode numbers, which would
severely hurt the performance. I don't expect this could be fix
anytime soon (or even there would be a fix), but it would be
worthwhile to surface this issue.
To manage notifications about this bug go to:
https://bugs.launchpad.net/qemu/+bug/1805913/+subscriptions
next prev parent reply other threads:[~2021-04-20 9:31 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-30 0:06 [Qemu-devel] [Bug 1805913] [NEW] readdir() returns NULL (errno=EOVERFLOW) for 32-bit user-static qemu on 64-bit host Ke Liu
2018-12-01 13:44 ` [Qemu-devel] [Bug 1805913] " Kan Li
2018-12-05 11:15 ` Alex Bennée
2019-04-16 13:20 ` diddly
2019-07-16 14:46 ` Alex Bennée
2019-08-01 13:00 ` diddly
2019-08-01 13:32 ` Peter Maydell
2020-01-30 8:19 ` Philippe Vaucher
2020-01-30 8:20 ` Philippe Vaucher
2020-01-30 10:47 ` diddly
2020-02-02 20:11 ` Philippe Vaucher
2020-02-02 21:01 ` Marcin Konarski
2020-02-06 13:34 ` Philippe Vaucher
2020-03-26 20:16 ` Peter Maydell
2020-03-27 15:19 ` Manuel Reimer
2020-03-27 16:00 ` Peter Maydell
2020-04-03 22:43 ` Eicke Herbertz
2021-04-20 8:11 ` Thomas Huth
2021-04-20 9:16 ` Peter Maydell [this message]
2021-05-11 5:36 ` Thomas Huth
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=161891019283.10217.14297973480552093714.malone@chaenomeles.canonical.com \
--to=1805913@bugs.launchpad.net \
--cc=qemu-devel@nongnu.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.