Commit 867046cc authored by David Laight's avatar David Laight Committed by Andrew Morton
Browse files

minmax: relax check to allow comparison between unsigned arguments and signed constants 

Allow (for example) min(unsigned_var, 20).

The opposite min(signed_var, 20u) is still errored.

Since a comparison between signed and unsigned never makes the unsigned
value negative it is only necessary to adjust the __types_ok() test.

Link: https://lkml.kernel.org/r/633b64e2f39e46bb8234809c5595b8c7@AcuMS.aculab.com


Signed-off-by: default avatarDavid Laight <david.laight@aculab.com>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Jason A. Donenfeld <Jason@zx2c4.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 4ead534f

include/linux/minmax.h

+17 −7
Original line number Diff line number Diff line
@@ -10,13 +10,18 @@ 
/*

 * min()/max()/clamp() macros must accomplish three things:

 *

 * - avoid multiple evaluations of the arguments (so side-effects like

 * - Avoid multiple evaluations of the arguments (so side-effects like

 *   "x++" happen only once) when non-constant.

 * - perform signed v unsigned type-checking (to generate compile

 *   errors instead of nasty runtime surprises).

 * - retain result as a constant expressions when called with only

 * - Retain result as a constant expressions when called with only

 *   constant expressions (to avoid tripping VLA warnings in stack

 *   allocation usage).

 * - Perform signed v unsigned type-checking (to generate compile

 *   errors instead of nasty runtime surprises).

 * - Unsigned char/short are always promoted to signed int and can be

 *   compared against signed or unsigned arguments.

 * - Unsigned arguments can be compared against non-negative signed constants.

 * - Comparison of a signed argument against an unsigned constant fails

 *   even if the constant is below __INT_MAX__ and could be cast to int.

 */

#define __typecheck(x, y) \

	(!!(sizeof((typeof(x) *)1 == (typeof(y) *)1)))
@@ -26,9 +31,14 @@ 
	__builtin_choose_expr(__is_constexpr(is_signed_type(typeof(x))),	\

		is_signed_type(typeof(x)), 0)



/* True for a non-negative signed int constant */

#define __is_noneg_int(x)	\

	(__builtin_choose_expr(__is_constexpr(x) && __is_signed(x), x, -1) >= 0)



#define __types_ok(x, y) 					\

	(__is_signed(x) == __is_signed(y) ||			\

		__is_signed((x) + 0) == __is_signed((y) + 0))

		__is_signed((x) + 0) == __is_signed((y) + 0) ||	\

		__is_noneg_int(x) || __is_noneg_int(y))



#define __cmp_op_min <

#define __cmp_op_max >