Bug 1346070

Summary: armv7hl: pwritev system call passes incorrect offset to kernel, always returns -EFBIG
Product: [Fedora] Fedora Reporter: Richard W.M. Jones <rjones>
Component: glibcAssignee: Carlos O'Donell <codonell>
Status: CLOSED RAWHIDE QA Contact: Fedora Extras Quality Assurance <extras-qa>
Severity: unspecified Docs Contact:
Priority: unspecified    
Version: rawhideCC: adhemerval.zanella, amit.shah, arjun.is, berrange, cfergeau, codonell, dj, dwmw2, fweimer, itamar, jakub, law, mfabian, pbonzini, pfrankli, rjones, siddhesh, virt-maint
Target Milestone: ---   
Target Release: ---   
Hardware: armv7hl   
OS: Unspecified   
Whiteboard:
Fixed In Version: glibc-2.23.90-24.fc25 Doc Type: If docs needed, set a value
Doc Text:
Story Points: ---
Clone Of: Environment:
Last Closed: 2016-07-05 16:39:26 UTC Type: Bug
Regression: --- Mount Type: ---
Documentation: --- CRM:
Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Embargoed:
Bug Depends On:    
Bug Blocks: 910269    
Attachments:
Description Flags
pwritev-test.c none

Description Richard W.M. Jones 2016-06-13 20:22:31 UTC 
Description of problem:

Note: This is on armv7hl only.

Simple qemu-img commands fail with odd errors, eg:

$ qemu-img create -f qcow2 -o preallocation=metadata blank-disk-1s.qcow2 512
qemu-img: blank-disk-1s.qcow2: The image size is too large for file format 'qcow2' (try using a larger cluster size)
Formatting 'blank-disk-1s.qcow2', fmt=qcow2 size=512 encryption=off cluster_size=65536 preallocation=metadata lazy_refcounts=off refcount_bits=16

$ qemu-img create -f qcow2 -o preallocation=metadata blank-disk-1K.qcow2 1K
qemu-img: blank-disk-1K.qcow2: The image size is too large for file format 'qcow2' (try using a larger cluster size)
Formatting 'blank-disk-1K.qcow2', fmt=qcow2 size=1024 encryption=off cluster_size=65536 preallocation=metadata lazy_refcounts=off refcount_bits=16

Version-Release number of selected component (if applicable):

qemu 2:2.6.0-3.fc25

How reproducible:

Unknown, but at least once.

Steps to Reproduce:
1. See commands above.
Comment 1 Richard W.M. Jones 2016-06-13 21:46:06 UTC 
Weirdly this does *not* happen with qemu 2:2.6.0-3.fc24.
The only apparent difference is F24 vs F25 (so glibc? kernel?)

I can reproduce this in upstream qemu on Rawhide/armv7l.
Comment 2 Richard W.M. Jones 2016-06-14 11:13:38 UTC 
Created attachment 1167837 [details]
pwritev-test.c

Please try the attached program with glibc-2.23.90-21.fc25.armv7hl

$ gcc -Wall pwritev-test.c -o pwritev-test
$ ./pwritev-test 
pwritev: File too large

It works on x86-64, and it also works on armv7 in Fedora 24.

The reason is because glibc is mangling (byte swapping, I think?)
the 'offset' parameter.  I passed offset = 32, but:

$ strace ./pwritev-test 
...
pwritev(3, [{"\0\0\0\0\0\0\0\0\0\0", 10}, {"\0\0\0\0\0\0", 6}], 2, 137438953472) = -1 EFBIG (File too large)

where 137438953472 == 0x2000000000
Comment 3 Carlos O'Donell 2016-06-14 17:26:25 UTC 
Might be caused by this.

commit af5fdf5a358329161cc3960f5e54fac16dbb8063
Author: Adhemerval Zanella <adhemerval.zanella>
Date:   Mon Apr 11 15:07:12 2016 -0300

    Consolidate pwritev/pwritev64 implementations
    
    This patch consolidates all the pwritev{64} implementation for Linux
    in only one (sysdeps/unix/sysv/linux/pwritev{64}.c).  It also removes the
    syscall from the auto-generation using assembly macros.
    
    It was based on previous pwrite/pwrite64 consolidation patch.  The new macro
    SYSCALL_LL{64} is used to handle the offset argument and alias is created
    for __ASSUME_OFF_DIFF_OFF64 in case of pread64.
    
    Checked on x86_64, i386, aarch64, and powerpc64le.
Comment 4 Adhemerval Zanella 2016-06-14 23:48:46 UTC 
I sent a fix for this issue for review [1].

[1] https://sourceware.org/ml/libc-alpha/2016-06/msg00559.html