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minmax: allow min()/max()/clamp() if the arguments have the same signedness.

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The type-check in min()/max() is there to stop unexpected results if a
negative value gets converted to a large unsigned value.  However it also
rejects 'unsigned int' v 'unsigned long' compares which are common and
never problematc.

Replace the 'same type' check with a 'same signedness' check.

The new test isn't itself a compile time error, so use static_assert() to
report the error and give a meaningful error message.

Due to the way builtin_choose_expr() works detecting the error in the
'non-constant' side (where static_assert() can be used) also detects
errors when the arguments are constant.

Link: https://lkml.kernel.org/r/fe7e6c542e094bfca655abcd323c1c98@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 08:17:15 +00:00 committed by Andrew Morton
parent 80fcac5538
commit d03eba99f5
1 changed files with 32 additions and 28 deletions
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60
include/linux/minmax.h
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@ -12,9 +12,8 @@
*
* - avoid multiple evaluations of the arguments (so side-effects like
* "x++" happen only once) when non-constant.
* - perform strict type-checking (to generate warnings instead of
* nasty runtime surprises). See the "unnecessary" pointer comparison
* in __typecheck().
* - 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
* constant expressions (to avoid tripping VLA warnings in stack
* allocation usage).
@ -22,23 +21,30 @@
#define __typecheck(x, y) \
(!!(sizeof((typeof(x) *)1 == (typeof(y) *)1)))
#define __no_side_effects(x, y) \
(__is_constexpr(x) && __is_constexpr(y))
/* is_signed_type() isn't a constexpr for pointer types */
#define __is_signed(x) \
__builtin_choose_expr(__is_constexpr(is_signed_type(typeof(x))), \
is_signed_type(typeof(x)), 0)
#define __safe_cmp(x, y) \
(__typecheck(x, y) && __no_side_effects(x, y))
#define __types_ok(x, y) \
(__is_signed(x) == __is_signed(y))
#define __cmp(x, y, op) ((x) op (y) ? (x) : (y))
#define __cmp_op_min <
#define __cmp_op_max >
#define __cmp_once(x, y, unique_x, unique_y, op) ({ \
#define __cmp(op, x, y) ((x) __cmp_op_##op (y) ? (x) : (y))
#define __cmp_once(op, x, y, unique_x, unique_y) ({ \
typeof(x) unique_x = (x); \
typeof(y) unique_y = (y); \
__cmp(unique_x, unique_y, op); })
static_assert(__types_ok(x, y), \
#op "(" #x ", " #y ") signedness error, fix types or consider u" #op "() before " #op "_t()"); \
__cmp(op, unique_x, unique_y); })
#define __careful_cmp(x, y, op) \
__builtin_choose_expr(__safe_cmp(x, y), \
__cmp(x, y, op), \
__cmp_once(x, y, __UNIQUE_ID(__x), __UNIQUE_ID(__y), op))
#define __careful_cmp(op, x, y) \
__builtin_choose_expr(__is_constexpr((x) - (y)), \
__cmp(op, x, y), \
__cmp_once(op, x, y, __UNIQUE_ID(__x), __UNIQUE_ID(__y)))
#define __clamp(val, lo, hi) \
((val) >= (hi) ? (hi) : ((val) <= (lo) ? (lo) : (val)))
@ -47,17 +53,15 @@
typeof(val) unique_val = (val); \
typeof(lo) unique_lo = (lo); \
typeof(hi) unique_hi = (hi); \
static_assert(__builtin_choose_expr(__is_constexpr((lo) > (hi)), \
(lo) <= (hi), true), \
"clamp() low limit " #lo " greater than high limit " #hi); \
static_assert(__types_ok(val, lo), "clamp() 'lo' signedness error"); \
static_assert(__types_ok(val, hi), "clamp() 'hi' signedness error"); \
__clamp(unique_val, unique_lo, unique_hi); })
#define __clamp_input_check(lo, hi) \
(BUILD_BUG_ON_ZERO(__builtin_choose_expr( \
__is_constexpr((lo) > (hi)), (lo) > (hi), false)))
#define __careful_clamp(val, lo, hi) ({ \
__clamp_input_check(lo, hi) + \
__builtin_choose_expr(__typecheck(val, lo) && __typecheck(val, hi) && \
__typecheck(hi, lo) && __is_constexpr(val) && \
__is_constexpr(lo) && __is_constexpr(hi), \
__builtin_choose_expr(__is_constexpr((val) - (lo) + (hi)), \
__clamp(val, lo, hi), \
__clamp_once(val, lo, hi, __UNIQUE_ID(__val), \
__UNIQUE_ID(__lo), __UNIQUE_ID(__hi))); })
@ -67,14 +71,14 @@
* @x: first value
* @y: second value
*/
#define min(x, y) __careful_cmp(x, y, <)
#define min(x, y) __careful_cmp(min, x, y)
/**
* max - return maximum of two values of the same or compatible types
* @x: first value
* @y: second value
*/
#define max(x, y) __careful_cmp(x, y, >)
#define max(x, y) __careful_cmp(max, x, y)
/**
* umin - return minimum of two non-negative values
@ -83,7 +87,7 @@
* @y: second value
*/
#define umin(x, y) \
__careful_cmp((x) + 0u + 0ul + 0ull, (y) + 0u + 0ul + 0ull, <)
__careful_cmp(min, (x) + 0u + 0ul + 0ull, (y) + 0u + 0ul + 0ull)
/**
* umax - return maximum of two non-negative values
@ -91,7 +95,7 @@
* @y: second value
*/
#define umax(x, y) \
__careful_cmp((x) + 0u + 0ul + 0ull, (y) + 0u + 0ul + 0ull, >)
__careful_cmp(max, (x) + 0u + 0ul + 0ull, (y) + 0u + 0ul + 0ull)
/**
* min3 - return minimum of three values
@ -143,7 +147,7 @@
* @x: first value
* @y: second value
*/
#define min_t(type, x, y) __careful_cmp((type)(x), (type)(y), <)
#define min_t(type, x, y) __careful_cmp(min, (type)(x), (type)(y))
/**
* max_t - return maximum of two values, using the specified type
@ -151,7 +155,7 @@
* @x: first value
* @y: second value
*/
#define max_t(type, x, y) __careful_cmp((type)(x), (type)(y), >)
#define max_t(type, x, y) __careful_cmp(max, (type)(x), (type)(y))
/*
* Do not check the array parameter using __must_be_array().