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    Subject[PATCH 3.16 258/410] nospec: Allow index argument to have const-qualified type
    3.16.57-rc1 review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Rasmus Villemoes <linux@rasmusvillemoes.dk>

    commit b98c6a160a057d5686a8c54c79cc6c8c94a7d0c8 upstream.

    The last expression in a statement expression need not be a bare
    variable, quoting gcc docs

    The last thing in the compound statement should be an expression
    followed by a semicolon; the value of this subexpression serves as the
    value of the entire construct.

    and we already use that in e.g. the min/max macros which end with a
    ternary expression.

    This way, we can allow index to have const-qualified type, which will in
    some cases avoid the need for introducing a local copy of index of
    non-const qualified type. That, in turn, can prevent readers not
    familiar with the internals of array_index_nospec from wondering about
    the seemingly redundant extra variable, and I think that's worthwhile
    considering how confusing the whole _nospec business is.

    The expression _i&_mask has type unsigned long (since that is the type
    of _mask, and the BUILD_BUG_ONs guarantee that _i will get promoted to
    that), so in order not to change the type of the whole expression, add
    a cast back to typeof(_i).

    Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
    Signed-off-by: Dan Williams <dan.j.williams@intel.com>
    Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Andy Lutomirski <luto@kernel.org>
    Cc: Arjan van de Ven <arjan@linux.intel.com>
    Cc: Borislav Petkov <bp@alien8.de>
    Cc: Dave Hansen <dave.hansen@linux.intel.com>
    Cc: David Woodhouse <dwmw2@infradead.org>
    Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    Cc: Josh Poimboeuf <jpoimboe@redhat.com>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: Will Deacon <will.deacon@arm.com>
    Cc: linux-arch@vger.kernel.org
    Link: http://lkml.kernel.org/r/151881604837.17395.10812767547837568328.stgit@dwillia2-desk3.amr.corp.intel.com
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
    ---
    include/linux/nospec.h | 3 +--
    1 file changed, 1 insertion(+), 2 deletions(-)

    --- a/include/linux/nospec.h
    +++ b/include/linux/nospec.h
    @@ -53,7 +53,6 @@ static inline unsigned long array_index_
    BUILD_BUG_ON(sizeof(_i) > sizeof(long)); \
    BUILD_BUG_ON(sizeof(_s) > sizeof(long)); \
    \
    - _i &= _mask; \
    - _i; \
    + (typeof(_i)) (_i & _mask); \
    })
    #endif /* _LINUX_NOSPEC_H */
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