This patch updates the container_of() implementation taken from the
Linux kernel.
We need to turn off -Wpointer-arith as the new container_of()
implementation does void pointer artihmetic as shown by this example
warning:
linux_helpers.h:43:26: warning: pointer of type ‘void *’ used in
arithmetic [-Wpointer-arith]
---
dlm_controld/Makefile | 2 +-
dlm_controld/linux_helpers.h | 36 ++++++++++++++++++++++++++++++++++++
dlm_controld/list.h | 12 +-----------
dlm_controld/rbtree.h | 2 +-
4 files changed, 39 insertions(+), 13 deletions(-)
diff --git a/dlm_controld/Makefile b/dlm_controld/Makefile
index 28b6bb0a..328a64ba 100644
--- a/dlm_controld/Makefile
+++ b/dlm_controld/Makefile
@@ -38,7 +38,7 @@ LIB_SOURCE = lib.c
CFLAGS += -D_GNU_SOURCE -O2 -ggdb \
-Wall -Wformat -Wformat-security -Wmissing-prototypes -Wnested-externs \
- -Wpointer-arith -Wextra -Wshadow -Wcast-align -Wwrite-strings \
+ -Wextra -Wshadow -Wcast-align -Wwrite-strings \
-Waggregate-return -Wstrict-prototypes -Winline -Wredundant-decls \
-Wno-sign-compare -Wno-unused-parameter -Wp,-D_FORTIFY_SOURCE=2 \
-fexceptions -fasynchronous-unwind-tables -fdiagnostics-show-option \
diff --git a/dlm_controld/linux_helpers.h b/dlm_controld/linux_helpers.h
index 5ef13466..09705cff 100644
--- a/dlm_controld/linux_helpers.h
+++ b/dlm_controld/linux_helpers.h
@@ -3,6 +3,42 @@
#ifndef __DLM_LINUX_HELPERS__
#define __DLM_LINUX_HELPERS__
+/*
+ * static_assert - check integer constant expression at build time
+ *
+ * static_assert() is a wrapper for the C11 _Static_assert, with a
+ * little macro magic to make the message optional (defaulting to the
+ * stringification of the tested expression).
+ *
+ * Contrary to BUILD_BUG_ON(), static_assert() can be used at global
+ * scope, but requires the expression to be an integer constant
+ * expression (i.e., it is not enough that __builtin_constant_p() is
+ * true for expr).
+ *
+ * Also note that BUILD_BUG_ON() fails the build if the condition is
+ * true, while static_assert() fails the build if the expression is
+ * false.
+ */
+#define static_assert(expr, ...) __static_assert(expr, ##__VA_ARGS__, #expr)
+#define __static_assert(expr, msg, ...) _Static_assert(expr, msg)
+
+#define __same_type(a, b) __builtin_types_compatible_p(typeof(a), typeof(b))
+
+/**
+ * container_of - cast a member of a structure out to the containing structure
+ * @ptr: the pointer to the member.
+ * @type: the type of the container struct this is embedded in.
+ * @member: the name of the member within the struct.
+ *
+ * WARNING: any const qualifier of @ptr is lost.
+ */
+#define container_of(ptr, type, member) ({ \
+ void *__mptr = (void *)(ptr); \
+ static_assert(__same_type(*(ptr), ((type *)0)->member) || \
+ __same_type(*(ptr), void), \
+ "pointer type mismatch in container_of()"); \
+ ((type *)(__mptr - offsetof(type, member))); })
+
#define WRITE_ONCE(x, val) \
do { \
*(volatile typeof(x) *)&(x) = (val); \
diff --git a/dlm_controld/list.h b/dlm_controld/list.h
index a2a5e5f3..e9df2ef2 100644
--- a/dlm_controld/list.h
+++ b/dlm_controld/list.h
@@ -3,17 +3,7 @@
#ifndef _LINUX_LIST_H
#define _LINUX_LIST_H
-/**
- * container_of - cast a member of a structure out to the containing structure
- *
- * @ptr: the pointer to the member.
- * @type: the type of the container struct this is embedded in.
- * @member: the name of the member within the struct.
- *
- */
-#define container_of(ptr, type, member) ({ \
- const typeof( ((type *)0)->member ) *__mptr = (ptr); \
- (type *)( (char *)__mptr - offsetof(type,member) );})
+#include "linux_helpers.h"
/*
* These are non-NULL pointers that will result in page faults
diff --git a/dlm_controld/rbtree.h b/dlm_controld/rbtree.h
index ddb86ff6..48b6e32f 100644
--- a/dlm_controld/rbtree.h
+++ b/dlm_controld/rbtree.h
@@ -20,7 +20,7 @@
#include <stdbool.h>
#include <string.h>
-#include "list.h"
+#include "linux_helpers.h"
#include "rbtree_types.h"
#define rb_parent(r) ((struct rb_node *)((r)->__rb_parent_color & ~3))
--
2.31.1
