Re: [Xen-devel] [PATCH v10 4/6] xen/x86: use DEFINE_SYMBOL as required

[Ian Jackson <ian.jackson@xxxxxxxxxx>]

Stefano Stabellini writes ("[PATCH v10 4/6] xen/x86: use DEFINE_SYMBOL as 
required"):
> Use SYMBOLS_SUBTRACT and SYMBOLS_COMPARE in cases of comparisons and
> subtractions of:
...
> Use explicit casts to uintptr_t when it is not possible to use the
> provided static inline functions.

Why is it not possible ?  You write:

> +/*
> + * Cannot use DEFINE_SYMBOL because of the way they are passed to
> + * apply_alternatives.
> + */
>  extern struct alt_instr __alt_instructions[], __alt_instructions_end[];

But I don't know why you can't pass a `struct abstract_alt_instr*' to
apply_alternatives.

IMO it should be strictly forbidden to ever write this formulation, as
you have above.  See my proposed rule comment for DEFINE_SYMBOL.

Even if you can't use the macros at some particular calculation site,
you should still ensure that ..._end has a different type, to make
sure that no unsafe uses escape.


FTR, I have not reviewed the rest of this patch yet.

Ian.

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