| From | Ben Hutchings <> | Date | Thu, 07 Jun 2018 15:05:21 +0100 | Subject | [PATCH 3.16 258/410] nospec: Allow index argument to have const-qualified type |
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3.16.57-rc1 review patch. If anyone has any objections, please let me know.
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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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