From: "Alex Bennée" <alex.bennee@linaro.org>
To: qemu-devel@nongnu.org
Subject: [Qemu-devel] [Bug 1805913] Re: readdir() returns NULL (errno=EOVERFLOW) for 32-bit user-static qemu on 64-bit host
Date: Tue, 16 Jul 2019 14:46:50 -0000 [thread overview]
Message-ID: <156328841096.15899.4463706161326562759.launchpad@soybean.canonical.com> (raw)
In-Reply-To: 154353638253.10384.17899256838547579767.malonedeb@chaenomeles.canonical.com
** Tags added: syscall-abi
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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:
New
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:[~2019-07-16 14:58 UTC|newest]
Thread overview: 21+ 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
2019-04-16 13:20 ` diddly
2019-07-16 14:46 ` Alex Bennée [this message]
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
2021-05-11 5:36 ` Thomas Huth
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