Re: [patch 2/8] compiler-gcc.h: add more comments to RELOC_HIDE

[Christoph Lameter]

On Sat, 10 Jan 2009, Ingo Molnar wrote:

> 2) Special structure sizes
>
>  For example we want to load a value from "&var + LARGE_OFFSET" (common
>  percpu construct). If 'var' is a C structure that happens to have a size
>  of 255 bytes, then GCC could legitimately assume that 'LARGE_OFFSET' is
>  0..255 [inclusive], and could optimize LARGE_OFFSET to be truncated to a
>  single byte.


But that is not what is occurring. We do not do &var + LARGE_OFFSET.
Instead one does

	((void *)&var) + LARGE_OFFSET

or
	((unsigned long)&var) + LARGE_OFFSET


The cast should cause the C compiler to drop all assumptions about size.
And the definition of RELOC_HIDE for icc and generic compilers in the tree
show that this is working.

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