From b1b864b398b2b7bc2ca54aca91b7abb1acee321d Mon Sep 17 00:00:00 2001
From: Theodore Ts'o <tytso@mit.edu>
Date: Sat, 23 Jan 2021 00:55:25 -0500
Subject: [PATCH] libext2fs: use compiler built-in offsetof() if available

This avoids UBSAN sanitizer warnings, since &(0->member) is
technically undefined per the C standard.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
---
 lib/ext2fs/compiler.h    | 22 ++++++++++++++++++++++
 lib/ext2fs/kernel-list.h |  4 +++-
 lib/ext2fs/rbtree.h      | 12 +-----------
 3 files changed, 26 insertions(+), 12 deletions(-)
 create mode 100644 lib/ext2fs/compiler.h

diff --git a/lib/ext2fs/compiler.h b/lib/ext2fs/compiler.h
new file mode 100644
index 0000000..9aa9b4e
--- /dev/null
+++ b/lib/ext2fs/compiler.h
@@ -0,0 +1,22 @@
+#ifndef _EXT2FS_COMPILER_H
+#define _EXT2FS_COMPILER_H
+
+#ifndef __has_builtin
+#define __has_builtin(x) 0
+#endif
+
+#undef offsetof
+#if __has_builtin(__builtin_offsetof)
+#define offsetof(TYPE, MEMBER) __builtin_offsetof(TYPE, MEMBER)
+#elif defined(__compiler_offsetof)
+#define offsetof(TYPE,MEMBER) __compiler_offsetof(TYPE,MEMBER)
+#else
+#define offsetof(TYPE, MEMBER) ((size_t) &((TYPE *)0)->MEMBER)
+#endif
+
+#define container_of(ptr, type, member) ({			\
+	const __typeof__( ((type *)0)->member ) *__mptr = (ptr);	\
+	(type *)( (char *)__mptr - offsetof(type,member) );})
+
+
+#endif /* _EXT2FS_COMPILER_H */
diff --git a/lib/ext2fs/kernel-list.h b/lib/ext2fs/kernel-list.h
index 01f4f6b..dd7b8e0 100644
--- a/lib/ext2fs/kernel-list.h
+++ b/lib/ext2fs/kernel-list.h
@@ -1,6 +1,8 @@
 #ifndef _LINUX_LIST_H
 #define _LINUX_LIST_H
 
+#include "compiler.h"
+
 /*
  * Simple doubly linked list implementation.
  *
@@ -101,7 +103,7 @@ static __inline__ void list_splice(struct list_head *list, struct list_head *hea
 }
 
 #define list_entry(ptr, type, member) \
-	((type *)((char *)(ptr)-(unsigned long)(&((type *)0)->member)))
+	container_of(ptr, type, member)
 
 #define list_for_each(pos, head) \
         for (pos = (head)->next; pos != (head); pos = pos->next)
diff --git a/lib/ext2fs/rbtree.h b/lib/ext2fs/rbtree.h
index 9e80677..dfeeb23 100644
--- a/lib/ext2fs/rbtree.h
+++ b/lib/ext2fs/rbtree.h
@@ -96,17 +96,7 @@ static inline struct page * rb_insert_page_cache(struct inode * inode,
 
 #include <stdlib.h>
 #include <stdint.h>
-
-#undef offsetof
-#ifdef __compiler_offsetof
-#define offsetof(TYPE,MEMBER) __compiler_offsetof(TYPE,MEMBER)
-#else
-#define offsetof(TYPE, MEMBER) ((size_t) &((TYPE *)0)->MEMBER)
-#endif
-
-#define container_of(ptr, type, member) ({			\
-	const __typeof__( ((type *)0)->member ) *__mptr = (ptr);	\
-	(type *)( (char *)__mptr - offsetof(type,member) );})
+#include "compiler.h"
 
 struct rb_node
 {
-- 
1.8.3.1