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

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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: David 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: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
David Laight 2023-09-18 08:19:25 +00:00 committed by Andrew Morton
parent 4ead534fba
commit 867046cc70
1 changed files with 17 additions and 7 deletions
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24
include/linux/minmax.h
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@ -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)
#define __types_ok(x, y) \
(__is_signed(x) == __is_signed(y) || \
__is_signed((x) + 0) == __is_signed((y) + 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_noneg_int(x) || __is_noneg_int(y))
#define __cmp_op_min <
#define __cmp_op_max >