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minmax: fix up min3() and max3() too

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David Laight pointed out that we should deal with the min3() and max3()
mess too, which still does excessive expansion.

And our current macros are actually rather broken.

In particular, the macros did this:

  #define min3(x, y, z) min((typeof(x))min(x, y), z)
  #define max3(x, y, z) max((typeof(x))max(x, y), z)

and that not only is a nested expansion of possibly very complex
arguments with all that involves, the typing with that "typeof()" cast
is completely wrong.

For example, imagine what happens in max3() if 'x' happens to be a
'unsigned char', but 'y' and 'z' are 'unsigned long'.  The types are
compatible, and there's no warning - but the result is just random
garbage.

No, I don't think we've ever hit that issue in practice, but since we
now have sane infrastructure for doing this right, let's just use it.
It fixes any excessive expansion, and also avoids these kinds of broken
type issues.

Requested-by: David Laight <David.Laight@aculab.com>
Acked-by: Arnd Bergmann <arnd@kernel.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Linus Torvalds 2024-07-30 15:44:16 -07:00
parent e4fc196f5b
commit 21b136cc63
1 changed files with 10 additions and 2 deletions
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12
include/linux/minmax.h
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@ -152,13 +152,20 @@
#define umax(x, y) \
__careful_cmp(max, (x) + 0u + 0ul + 0ull, (y) + 0u + 0ul + 0ull)
#define __careful_op3(op, x, y, z, ux, uy, uz) ({ \
__auto_type ux = (x); __auto_type uy = (y);__auto_type uz = (z);\
BUILD_BUG_ON_MSG(!__types_ok3(x,y,z,ux,uy,uz), \
#op"3("#x", "#y", "#z") signedness error"); \
__cmp(op, ux, __cmp(op, uy, uz)); })
/**
* min3 - return minimum of three values
* @x: first value
* @y: second value
* @z: third value
*/
#define min3(x, y, z) min((typeof(x))min(x, y), z)
#define min3(x, y, z) \
__careful_op3(min, x, y, z, __UNIQUE_ID(x_), __UNIQUE_ID(y_), __UNIQUE_ID(z_))
/**
* max3 - return maximum of three values
@ -166,7 +173,8 @@
* @y: second value
* @z: third value
*/
#define max3(x, y, z) max((typeof(x))max(x, y), z)
#define max3(x, y, z) \
__careful_op3(max, x, y, z, __UNIQUE_ID(x_), __UNIQUE_ID(y_), __UNIQUE_ID(z_))
/**
* min_not_zero - return the minimum that is _not_ zero, unless both are zero