Messages in this thread Patch in this message |  | | From | Ian Abbott <> | Subject | [PATCH] kernel.h: handle pointers to arrays better in container_of() | Date | Mon, 10 Oct 2016 21:16:02 +0100 |
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If the first parameter of container_of() is a pointer to a non-const-qualified array type, the local variable __mptr will be defined with a const-qualified array type. In ISO C, these types are incompatible. They work as expected in GNU C, but some versions will issue warnings. For example, GCC 4.9 produces the warning "initialization from incompatible pointer type". Fix it by avoiding defining the __mptr variable. This also avoids other GCC extensions.
The container_of_safe() macro has the same problem. Here, we cannot avoid all GCC extensions without eliminating possible side-effects, but we can avoid having pointers to differently qualified array types.
Signed-off-by: Ian Abbott <abbotti@mev.co.uk> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Michal Nazarewicz <mina86@mina86.com> Cc: Hidehiro Kawai <hidehiro.kawai.ez@hitachi.com> Cc: Borislav Petkov <bp@suse.de> Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk> Cc: Johannes Berg <johannes.berg@intel.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Alexander Potapenko <glider@google.com> --- include/linux/kernel.h | 11 +++++------ 1 file changed, 5 insertions(+), 6 deletions(-)
diff --git a/include/linux/kernel.h b/include/linux/kernel.h index c64f998..5117b9f 100644 --- a/include/linux/kernel.h +++ b/include/linux/kernel.h @@ -832,9 +832,8 @@ static inline void ftrace_dump(enum ftrace_dump_mode oops_dump_mode) { } * @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) );}) +#define container_of(ptr, type, member) \ + ((type *)((char *)(ptr) - offsetof(type, member))) /** * container_of_safe - safe version of container_of @@ -846,9 +845,9 @@ static inline void ftrace_dump(enum ftrace_dump_mode oops_dump_mode) { } * @type, return 0. */ #define container_of_safe(ptr, type, member) ({ \ - const typeof( ((type *)0)->member ) *__mptr = (ptr); \ - (size_t)__mptr >= offsetof(type,member) ? \ - (type *)( (char *)__mptr - offsetof(type,member) ) : (type *)0 ;}) + char *__mptr = (char *)(ptr); \ + (size_t)__mptr >= offsetof(type, member) ? \ + (type *)(__mptr - offsetof(type, member)) : (type *)0; }) /* Rebuild everything on CONFIG_FTRACE_MCOUNT_RECORD */ -- 2.9.3
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