On 04/25/2012 01:56 PM, Greg Kroah-Hartman wrote: > On Wed, Apr 25, 2012 at 09:35:25AM -0400, Nitin Gupta wrote: >> On 04/25/2012 02:23 AM, Minchan Kim wrote: >> >>> Let's remove unnecessary type casting of (void *). >>> >>> Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx> >>> --- >>> drivers/staging/zsmalloc/zsmalloc-main.c | 3 +-- >>> 1 file changed, 1 insertion(+), 2 deletions(-) >>> >>> diff --git a/drivers/staging/zsmalloc/zsmalloc-main.c b/drivers/staging/zsmalloc/zsmalloc-main.c >>> index b7d31cc..ff089f8 100644 >>> --- a/drivers/staging/zsmalloc/zsmalloc-main.c >>> +++ b/drivers/staging/zsmalloc/zsmalloc-main.c >>> @@ -644,8 +644,7 @@ void zs_free(struct zs_pool *pool, void *obj) >>> spin_lock(&class->lock); >>> >>> /* Insert this object in containing zspage's freelist */ >>> - link = (struct link_free *)((unsigned char *)kmap_atomic(f_page) >>> - + f_offset); >>> + link = (struct link_free *)(kmap_atomic(f_page) + f_offset); >>> link->next = first_page->freelist; >>> kunmap_atomic(link); >>> first_page->freelist = obj; >> >> >> >> Incrementing a void pointer looks weired and should not be allowed by C >> compilers though gcc and clang seem to allow this without any warnings. >> (fortunately C++ forbids incrementing void pointers) > > Huh? A void pointer can safely be incremented by C I thought, do you > have a pointer to where in the reference it says it is "unspecified"? > Arithmetic on void pointers and function pointers is listed as a GNU C extension, so I don't think these operations are part of C standard. >From info gcc (section 6.23): """ 6.23 Arithmetic on `void'- and Function-Pointers In GNU C, addition and subtraction operations are supported on pointers to `void' and on pointers to functions. This is done by treating the size of a `void' or of a function as 1. A consequence of this is that `sizeof' is also allowed on `void' and on function types, and returns 1. The option `-Wpointer-arith' requests a warning if these extensions are used. """ >> So, we should keep this cast to unsigned char pointer to avoid relying >> on a non-standard, compiler specific behavior. > > I do agree about this, more people are starting to build the kernel with > other compilers than gcc, so it would be nice to ensure that we get > stuff like this right. > As an example, MSVC does not support arithmetic on void pointers: http://stackoverflow.com/questions/1864352/pointer-arithmetic-when-void-has-unknown-size Thanks, Nitin -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>