On 07/09/2012 03:24 PM, Eric Sandeen wrote:
On 7/8/12 1:07 AM, Jon Masters wrote:
On 07/07/2012 08:42 PM, Gordan Bobic wrote:
Can anyone confirm whether this has been fixed since the bug was filed?
Or whether there is still a risk of trashing the file system on ARMv5/ARMv6?
https://bugzilla.redhat.com/show_bug.cgi?id=680090
I believe Eric said this was now likely fixed upstream. Have you asked
him to confirm? Let me copy him, and I'm sure he'll say it's all fine :)
nope, sorry - well, not exactly fine. ;)
We fixed on-disk structure alignment errors for XFS - this is a different
problem, with in-memory alignment...
These memory access problem on arm may well still exist.
It's "only" a warning about alignment though, right - I don't think this
results in any corruption etc, does it (anyway, filefrag is read-only).
What concerns me is that the buffers are allocated as char[4096] all
over the place in e2fsprogs code files. That is inherently unsafe on
everything except x86 and ARMv7+. I wouldn't want to assume that
filefrag is the only affected program from the e2fsprogs suite,
especially since the scope for trashing the file system is pretty high.
And as the comments in this bug indicate, I'm really not quite sure what
the accepted method of fixing is.
The options I can see are:
1) Detect sizeof(int) and declare the arrays as a suitable multiple of
that. int _should_ be word sized on most things AFAIK.
2) Check the required alignment for the arch at build time, and apply it
with "__attribute__ aligned" in every relevant instance. There's a LOT
of those, but that's what you get for using non-portable techniques. :(
3) Add a new flag to gcc to align all arrays to a particular boundary.
Unlikely to happen. FWIW, ICC has such an option, IIRC as it helps with
performance, too, if things aren't straddling cache lines.
I imagine there are several applications
that exhibit similar behavior?
Not many, if you are referring to other packages. I filed bugs for most
of them, but I filed against the available ARM releases (since rawhide
wasn't up to running on ARM), so they all got closed without resolution
pretty quickly. I gave up on bothering to file bugs after that.
Gordan
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