RE: [PATCH 1/2] selftests: Provide local define of min() and max()

From: Willem de Bruijn

Sent: Sunday, August 20, 2023 4:15 PM

Mahmoud Maatuq wrote:

quoted

to avoid manual calculation of min and max values
and fix coccinelle warnings such WARNING opportunity for min()/max()
adding one common definition that could be used in multiple files
under selftests.
there are also some defines for min/max scattered locally inside sources
under selftests.
this also prepares for cleaning up those redundant defines and include
kselftest.h instead.

Signed-off-by: Mahmoud Maatuq <redacted>
---
 tools/testing/selftests/kselftest.h | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/tools/testing/selftests/kselftest.h b/tools/testing/selftests/kselftest.h
index 829be379545a..e8eb7e9afbc6 100644
--- a/tools/testing/selftests/kselftest.h
+++ b/tools/testing/selftests/kselftest.h

@@ -55,6 +55,13 @@
 #define ARRAY_SIZE(arr) (sizeof(arr) / sizeof((arr)[0]))
 #endif

+#ifndef min
+# define min(x, y) ((x) < (y) ? (x) : (y))
+#endif
+#ifndef max
+# define max(x, y) ((x) < (y) ? (y) : (x))
+#endif
+

Should this more closely follow include/linux/minmax.h, which is a lot
more strict?

I'm fine with this simpler, more relaxed, version for testing, but
calling it out for people to speak up.

Only the first two of these comments in minmax.h apply to this
userspace code.

/*
 * min()/max()/clamp() macros must accomplish three things:
 *
 * - 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().
 * - retain result as a constant expressions when called with only
 *   constant expressions (to avoid tripping VLA warnings in stack
 *   allocation usage).
 */

Note that a more strict version that includes __typecheck would
warn on the type difference between total_len and cfg_mss. Fine
with changing the type of cfg_mss in the follow-on patch to address
that.

That typecheck() is horrid.
It may well have caused more bugs due to incorrect casts that
it actually detected.

I'd suggest the version that just avoids multiple evaluations.
Or just error signed v unsigned comparisons.
See  https://lore.kernel.org/all/b4ce9dad748e489f9314a2dc95615033@AcuMS.aculab.com/ (local)
for an example patch set.

	David

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