Re: [PATCH-mm 1/8] ntfs: remove private wrapper around endian helpers

From: Anton Altaparmakov
Date: Mon Dec 01 2008 - 03:50:27 EST


On 27 Nov 2008, at 19:35, Harvey Harrison wrote:
On Thu, 2008-11-27 at 08:22 +0000, Anton Altaparmakov wrote:
On 26 Nov 2008, at 21:12, Harvey Harrison wrote:
The base versions handle constant folding just fine.
Done with sed other than the mft.c and inode.c one-liners.

Have you checked the compiler output? And on all architectures? And
on all gcc versions?

Yes I've checked the compiler output for the new byteorder helpers
for gcc 3.4, 4, 4.2 on x86.

Notice this depends on the byteorder bits in -mm. The failure of
the old bits to properly compile-time swap I've only seen at -O0,
which the new bits do properly. If you can cite a particular
version/arch that you know of where the bug arose, please let me

Ah, I failed to notice this required some new byteorder code! Sorry.

The reason I introduced the constant version are precisely that at
least some versions of gcc at least on some architectures do NOT
handle the constant folding and actually put in endianness conversion
code for the constants instead of converting them at compile time.

Which ones....-O0 builds perhaps?

Also you are breaking sparse checking with this patch as you remove
some of the necessary endianness conversions (e.g. your one liner in
mft.c which causes us to apply a binary 'not' operator on a little
endian which sparse complains about - in fact that is the reason the
endianness conversions are in there in the first place - I added them
because sparse was complaining about them).

No, sparse does not complain about it. Bitwise operations are just
fine on types such as le16 etc. Try running sparse again with
my changes, there are no new warnings.

Interesting. Sparse must have grown up then. It used to complain (although I always thought it was complaining incorrectly given that binary bit operations are endianness agnostic).

Andrew, please do not apply this patch.

I hope you change you mind.

Yes, you have convinced me. (-:

Andrew, please feel free to apply the patch.

Best regards,

Anton Altaparmakov <aia21 at> (replace at with @)
Unix Support, Computing Service, University of Cambridge, CB2 3QH, UK
Linux NTFS maintainer,

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