On Oct. 22, 2007, 22:16 +0200, Alan Cox <alan@xxxxxxxxxxxxxxxxxxx> wrote:
On Mon, 22 Oct 2007 12:49:40 -0700 (PDT)
Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
On Mon, 22 Oct 2007, Geert Uytterhoeven wrote:
Better safe than sorry...
Is it possible that a chain entry pointer has bit 1 set on architectures
(e.g. m68k) where the natural alignment of 32-bit quantities is _2_ bytes,
not 4?
Better make sure that such alignment never happens... But no, I don't
think it will, since these things would generally always have to be
allocated with an allocator, and the *allocator* won't return 2-byte
aligned data structures.
No - but a structure which has other objects in it before the object
being written out may well be 2 byte aligned on M68K and some of the
other externally 16bit platforms - ditto local dynamic objects.
Why can't we just make the list one item longer than the entry count and
stick a NULL on the end of it like normal people ? Then you need one bit
which ought to be safe for everyone (and if the bit is a macro any CPU
warped enough to have byte alignment is surely going to have top bits
spare...)
Alternatively, I proposed to check for end of list in sg_next
by calling it with the next iterator value and number of list elements.
We tried that patch here and it seems like a reasonable alternative.
If folks are interested, I can send the full patch for review.
Alan
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