linux-kernel - [RFC PATCH v2 5/8] tools/nolibc/types: Implement `offsetof()` and `container

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Date:   Tue, 22 Mar 2022 17:21:12 +0700
From:   Ammar Faizi <ammarfaizi2@...weeb.org>
To:     Willy Tarreau <w@....eu>
Cc:     "Paul E. McKenney" <paulmck@...nel.org>,
        Alviro Iskandar Setiawan <alviro.iskandar@...weeb.org>,
        Nugraha <richiisei@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        GNU/Weeb Mailing List <gwml@...r.gnuweeb.org>,
        Ammar Faizi <ammarfaizi2@...weeb.org>
Subject: [RFC PATCH v2 5/8] tools/nolibc/types: Implement `offsetof()` and `container_of()` macro

Implement `offsetof()` and `container_of()` macro. The first use case
of these macros is for `malloc()`, `realloc()` and `free()`.

Signed-off-by: Ammar Faizi <ammarfaizi2@...weeb.org>
---
 tools/include/nolibc/types.h | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/tools/include/nolibc/types.h b/tools/include/nolibc/types.h
index 357e60ad38a8..959997034e55 100644
--- a/tools/include/nolibc/types.h
+++ b/tools/include/nolibc/types.h
@@ -191,4 +191,15 @@ struct stat {
 #define major(dev) ((unsigned int)(((dev) >> 8) & 0xfff))
 #define minor(dev) ((unsigned int)(((dev) & 0xff))
 
+#ifndef offsetof
+#define offsetof(TYPE, FIELD) ((size_t) &((TYPE *)0)->FIELD)
+#endif
+
+#ifndef container_of
+#define container_of(PTR, TYPE, FIELD) ({			\
+	__typeof__(((TYPE *)0)->FIELD) *__FIELD_PTR = (PTR);	\
+	(TYPE *)((char *) __FIELD_PTR - offsetof(TYPE, FIELD));	\
+})
+#endif
+
 #endif /* _NOLIBC_TYPES_H */
-- 
Ammar Faizi