Re: [PATCH] kernel.h: fix new warnings for container_of()

From: Ian Abbott
Date: Wed Jun 21 2017 - 05:25:41 EST

On 20/06/17 21:09, Arnd Bergmann wrote:
I see new warnings with gcc-7.0.1 with the modified container_of():

fs/f2fs/dir.c: In function 'F2FS_I':
fs/f2fs/f2fs.h:1122:385: note: found mismatched ssa struct pointer types: 'struct f2fs_inode_info' and 'struct inode'

Is that actually a warning, or just informational? In any case, it seems like a good idea to avoid it.

This seems to happen for all structures that have a zero offset
between the member and the container structure, i.e. idential

Reverting to an intermediate pointer avoids the warning, and using
a void pointer instead of the target type should also avoid
regressing on the previous patch again.

Fixes: mmotm ("kernel.h: handle pointers to arrays better in container_of()")
Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
include/linux/kernel.h | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index d043adadcf33..bd6d96cf80b1 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -856,10 +856,11 @@ static inline void ftrace_dump(enum ftrace_dump_mode oops_dump_mode) { }
#define container_of(ptr, type, member) ({ \
+ void *__mptr = (void *)(ptr); \
BUILD_BUG_ON_MSG(!__same_type(*(ptr), ((type *)0)->member) && \
!__same_type(*(ptr), void), \
"pointer type mismatch in container_of()"); \
- ((type *)((char *)(ptr) - offsetof(type, member))); })
+ ((type *)(__mptr - offsetof(type, member))); })

/* Rebuild everything on CONFIG_FTRACE_MCOUNT_RECORD */

Acked-by: Ian Abbott <abbotti@xxxxxxxxx>

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