[PATCH] Fix sparse checks processing

[Christophe Leroy]

A lot of errors are encountered when building with sparse checking
activated (make C=1 or make C=2).

Many of them are fixed in Linux.

Resynchronise Makefile and include/linux/build_bug.h with Linux
kernel sources by porting the following Linux commits into u-boot:
- 6c49f359ca14 ("kbuild: disable sparse warnings about unknown attributes")
- 80591e61a0f7 ("kbuild: tell sparse about the $ARCH")
- 8788994376d8 ("linux/build_bug.h: change type to int")
- 527edbc18a70 ("build_bug.h: remove most of dummy BUILD_BUG_ON stubs for Sparse")
- c60d3b79423a ("build_bug.h: remove negative-array fallback for BUILD_BUG_ON()")
- 14e83077d55f ("include: drop pointless __compiler_offsetof indirection")

Also revert commit aa9e891c63 ("include/linux/stddef.h: avoid
'warning: preprocessor token offsetof redefined'") because the
error it creates is worse than the warning it is trying to fix.

Signed-off-by: Christophe Leroy <christophe.leroy at csgroup.eu>
---
 Makefile                  |  6 +++++-
 include/linux/build_bug.h | 40 ++++++++-------------------------------
 include/linux/stddef.h    |  8 +-------
 3 files changed, 14 insertions(+), 40 deletions(-)

diff --git a/Makefile b/Makefile
index 4f4f014d2c..6bf62ebad6 100644
--- a/Makefile
+++ b/Makefile
@@ -423,7 +423,8 @@ DTC_MIN_VERSION	:= 010406
 CHECK		= sparse
 
 CHECKFLAGS     := -D__linux__ -Dlinux -D__STDC__ -Dunix -D__unix__ \
-		  -Wbitwise -Wno-return-void -D__CHECK_ENDIAN__ $(CF)
+		  -Wbitwise -Wno-return-void -Wno-unknown-attribute \
+		  -D__CHECK_ENDIAN__ $(CF)
 
 KBUILD_CPPFLAGS := -D__KERNEL__ -D__UBOOT__
 
@@ -1032,6 +1033,9 @@ ifeq ($(CONFIG_ARC)$(CONFIG_NIOS2)$(CONFIG_X86)$(CONFIG_XTENSA),)
 LDFLAGS_u-boot += -Ttext $(CONFIG_TEXT_BASE)
 endif
 
+# make the checker run with the right architecture
+CHECKFLAGS += --arch=$(ARCH)
+
 # insure the checker run with the right endianness
 CHECKFLAGS += $(if $(CONFIG_CPU_BIG_ENDIAN),-mbig-endian,-mlittle-endian)
 
diff --git a/include/linux/build_bug.h b/include/linux/build_bug.h
index 9c7088bafa..20c2dc7f4b 100644
--- a/include/linux/build_bug.h
+++ b/include/linux/build_bug.h
@@ -4,15 +4,16 @@
 #include <linux/compiler.h>
 
 #ifdef __CHECKER__
-#define __BUILD_BUG_ON_NOT_POWER_OF_2(n) (0)
-#define BUILD_BUG_ON_NOT_POWER_OF_2(n) (0)
 #define BUILD_BUG_ON_ZERO(e) (0)
-#define BUILD_BUG_ON_NULL(e) ((void *)0)
-#define BUILD_BUG_ON_INVALID(e) (0)
-#define BUILD_BUG_ON_MSG(cond, msg) (0)
-#define BUILD_BUG_ON(condition) (0)
-#define BUILD_BUG() (0)
 #else /* __CHECKER__ */
+/*
+ * Force a compilation error if condition is true, but also produce a
+ * result (of value 0 and type int), so the expression can be used
+ * e.g. in a structure initializer (or where-ever else comma expressions
+ * aren't permitted).
+ */
+#define BUILD_BUG_ON_ZERO(e) ((int)sizeof(struct { int:(-!!(e)); }))
+#endif	/* __CHECKER__ */
 
 /* Force a compilation error if a constant expression is not a power of 2 */
 #define __BUILD_BUG_ON_NOT_POWER_OF_2(n)	\
@@ -20,15 +21,6 @@
 #define BUILD_BUG_ON_NOT_POWER_OF_2(n)			\
 	BUILD_BUG_ON((n) == 0 || (((n) & ((n) - 1)) != 0))
 
-/*
- * Force a compilation error if condition is true, but also produce a
- * result (of value 0 and type size_t), so the expression can be used
- * e.g. in a structure initializer (or where-ever else comma expressions
- * aren't permitted).
- */
-#define BUILD_BUG_ON_ZERO(e) (sizeof(struct { int:(-!!(e)); }))
-#define BUILD_BUG_ON_NULL(e) ((void *)sizeof(struct { int:(-!!(e)); }))
-
 /*
  * BUILD_BUG_ON_INVALID() permits the compiler to check the validity of the
  * expression but avoids the generation of any code, even if that expression
@@ -52,23 +44,9 @@
  * If you have some code which relies on certain constants being equal, or
  * some other compile-time-evaluated condition, you should use BUILD_BUG_ON to
  * detect if someone changes it.
- *
- * The implementation uses gcc's reluctance to create a negative array, but gcc
- * (as of 4.4) only emits that error for obvious cases (e.g. not arguments to
- * inline functions).  Luckily, in 4.3 they added the "error" function
- * attribute just for this type of case.  Thus, we use a negative sized array
- * (should always create an error on gcc versions older than 4.4) and then call
- * an undefined function with the error attribute (should always create an
- * error on gcc 4.3 and later).  If for some reason, neither creates a
- * compile-time error, we'll still have a link-time error, which is harder to
- * track down.
  */
-#ifndef __OPTIMIZE__
-#define BUILD_BUG_ON(condition) ((void)sizeof(char[1 - 2*!!(condition)]))
-#else
 #define BUILD_BUG_ON(condition) \
 	BUILD_BUG_ON_MSG(condition, "BUILD_BUG_ON failed: " #condition)
-#endif
 
 /**
  * BUILD_BUG - break compile if used.
@@ -98,6 +76,4 @@
 #define static_assert(expr, ...) __static_assert(expr, ##__VA_ARGS__, #expr)
 #define __static_assert(expr, msg, ...) _Static_assert(expr, msg)
 
-#endif	/* __CHECKER__ */
-
 #endif	/* _LINUX_BUILD_BUG_H */
diff --git a/include/linux/stddef.h b/include/linux/stddef.h
index a7f546fdfe..c732eef65a 100644
--- a/include/linux/stddef.h
+++ b/include/linux/stddef.h
@@ -14,13 +14,7 @@
 #include <linux/types.h>
 #endif
 
-#ifndef __CHECKER__
 #undef offsetof
-#ifdef __compiler_offsetof
-#define offsetof(TYPE, MEMBER)	__compiler_offsetof(TYPE, MEMBER)
-#else
-#define offsetof(TYPE, MEMBER)	((size_t)&((TYPE *)0)->MEMBER)
-#endif
-#endif
+#define offsetof(TYPE, MEMBER)	__builtin_offsetof(TYPE, MEMBER)
 
 #endif
-- 
2.39.2