From 7aa7c7be6e803de267a165237e23577ab496e792 Mon Sep 17 00:00:00 2001

From: Vishal Verma <vishal.l.verma@intel.com>

Date: Thu, 7 Oct 2021 02:21:26 -0600

Subject: [PATCH 034/217] util: add the struct_size() helper from the kernel

Add struct_size() from include/linux/overflow.h which calculates the

size of a struct with a trailing variable length array.

Suggested-by: Dan Williams <dan.j.williams@intel.com>

Reviewed-by: Dan Williams <dan.j.williams@intel.com>

Signed-off-by: Vishal Verma <vishal.l.verma@intel.com>

---

 util/size.h | 62 +++++++++++++++++++++++++++++++++++++++++++++++++++++

 util/util.h |  6 ++++++

 2 files changed, 68 insertions(+)

diff --git a/util/size.h b/util/size.h

index 646edae..a0f3593 100644

--- a/util/size.h

+++ b/util/size.h

@@ -4,6 +4,8 @@

 #ifndef _NDCTL_SIZE_H_

 #define _NDCTL_SIZE_H_

 #include <stdbool.h>

+#include <stdint.h>

+#include <util/util.h>

 #define SZ_1K     0x00000400

 #define SZ_4K     0x00001000

@@ -30,4 +32,64 @@ static inline bool is_power_of_2(unsigned long long v)

 #define BITS_PER_LONG (sizeof(unsigned long) * 8)

 #define HPAGE_SIZE (2 << 20)

+/*

+ * Helpers for struct_size() copied from include/linux/overflow.h (GPL-2.0)

+ *

+ * For simplicity and code hygiene, the fallback code below insists on

+ * a, b and *d having the same type (similar to the min() and max()

+ * macros), whereas gcc's type-generic overflow checkers accept

+ * different types. Hence we don't just make check_add_overflow an

+ * alias for __builtin_add_overflow, but add type checks similar to

+ * below.

+ */

+#define check_add_overflow(a, b, d) (({	\

+	typeof(a) __a = (a);			\

+	typeof(b) __b = (b);			\

+	typeof(d) __d = (d);			\

+	(void) (&__a == &__b);			\

+	(void) (&__a == __d);			\

+	__builtin_add_overflow(__a, __b, __d);	\

+}))

+

+#define check_mul_overflow(a, b, d) (({	\

+	typeof(a) __a = (a);			\

+	typeof(b) __b = (b);			\

+	typeof(d) __d = (d);			\

+	(void) (&__a == &__b);			\

+	(void) (&__a == __d);			\

+	__builtin_mul_overflow(__a, __b, __d);	\

+}))

+

+/*

+ * Compute a*b+c, returning SIZE_MAX on overflow. Internal helper for

+ * struct_size() below.

+ */

+static inline size_t __ab_c_size(size_t a, size_t b, size_t c)

+{

+	size_t bytes;

+

+	if (check_mul_overflow(a, b, &bytes))

+		return SIZE_MAX;

+	if (check_add_overflow(bytes, c, &bytes))

+		return SIZE_MAX;

+

+	return bytes;

+}

+

+/**

+ * struct_size() - Calculate size of structure with trailing array.

+ * @p: Pointer to the structure.

+ * @member: Name of the array member.

+ * @count: Number of elements in the array.

+ *

+ * Calculates size of memory needed for structure @p followed by an

+ * array of @count number of @member elements.

+ *

+ * Return: number of bytes needed or SIZE_MAX on overflow.

+ */

+#define struct_size(p, member, count)					\

+	__ab_c_size(count,						\

+		    sizeof(*(p)->member) + __must_be_array((p)->member),\

+		    sizeof(*(p)))

+

 #endif /* _NDCTL_SIZE_H_ */

diff --git a/util/util.h b/util/util.h

index ae0e4e1..b2b4ae6 100644

--- a/util/util.h

+++ b/util/util.h

@@ -63,6 +63,12 @@

 #define BUILD_BUG_ON_ZERO(e) (sizeof(struct { int:-!!(e); }))

 #define BUILD_BUG_ON(condition) ((void)sizeof(char[1 - 2*!!(condition)]))

+/* Are two types/vars the same type (ignoring qualifiers)? */

+#define __same_type(a, b) __builtin_types_compatible_p(typeof(a), typeof(b))

+

+/* &a[0] degrades to a pointer: a different type from an array */

+#define __must_be_array(a)	BUILD_BUG_ON_ZERO(__same_type((a), &(a)[0]))

+

 enum {

 	READ, WRITE,

 };

-- 

2.27.0