linux-kernel - [PATCH 1/2] lib: test_scanf: Fix incorrect use of type

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Date:   Mon, 24 May 2021 16:59:40 +0100
From:   Richard Fitzgerald <rf@...nsource.cirrus.com>
To:     <pmladek@...e.com>, <rostedt@...dmis.org>,
        <sergey.senozhatsky@...il.com>,
        <andriy.shevchenko@...ux.intel.com>, <linux@...musvillemoes.dk>,
        <w@....eu>, <lkml@....org>, <davem@...emloft.net>,
        <kuba@...nel.org>
CC:     <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <patches@...nsource.cirrus.com>,
        Richard Fitzgerald <rf@...nsource.cirrus.com>
Subject: [PATCH 1/2] lib: test_scanf: Fix incorrect use of type_min() with unsigned types

sparse was producing warnings of the form:

 sparse: cast truncates bits from constant value (ffff0001 becomes 1)

The problem was that value_representable_in_type() compared unsigned types
against type_min(). But type_min() is only valid for signed types because
it is calculating the value -type_max() - 1. The minimum value of an
unsigned is obviously 0, so only type_max() need be tested.

This patch also takes the opportunity to clean up the implementation of
simple_numbers_loop() to use a common pattern for the positive and
negative test.

Reported-by: kernel test robot <lkp@...el.com>
Fixes: 17aadada455d ("lib: test_scanf: Add tests for sscanf number conversion")
Signed-off-by: Richard Fitzgerald <rf@...nsource.cirrus.com>
---
 lib/test_scanf.c | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/lib/test_scanf.c b/lib/test_scanf.c
index 8d577aec6c28..48ff5747a4da 100644
--- a/lib/test_scanf.c
+++ b/lib/test_scanf.c
@@ -187,8 +187,8 @@ static const unsigned long long numbers[] __initconst = {
 #define value_representable_in_type(T, val)					 \
 (is_signed_type(T)								 \
 	? ((long long)(val) >= type_min(T)) && ((long long)(val) <= type_max(T)) \
-	: ((unsigned long long)(val) >= type_min(T)) &&				 \
-	  ((unsigned long long)(val) <= type_max(T)))
+	: ((unsigned long long)(val) <= type_max(T)))
+
 
 #define test_one_number(T, gen_fmt, scan_fmt, val, fn)			\
 do {									\
@@ -204,12 +204,11 @@ do {									\
 	int i;								\
 									\
 	for (i = 0; i < ARRAY_SIZE(numbers); i++) {			\
-		if (!value_representable_in_type(T, numbers[i]))	\
-			continue;					\
-									\
-		test_one_number(T, gen_fmt, scan_fmt, numbers[i], fn);	\
+		if (value_representable_in_type(T, numbers[i]))		\
+			test_one_number(T, gen_fmt, scan_fmt,		\
+					numbers[i], fn);		\
 									\
-		if (is_signed_type(T))					\
+		if (value_representable_in_type(T, -numbers[i]))	\
 			test_one_number(T, gen_fmt, scan_fmt,		\
 					-numbers[i], fn);		\
 	}								\
-- 
2.20.1