On Sat, Feb 02, 2013 at 10:03:43PM -0500, Theodore Ts'o wrote:
> On Wed, Jan 30, 2013 at 10:43:33AM +0800, Zheng Liu wrote:
> >
> > Clang is first coming in my mind. I know that some one try to use it
> > to build a linux kernel and get a lot of problems that are about gcc
> > extension. But for us it seems that things are not too bad. ;)
>
> Clang accepts bitfields with "unsigned long long", but I've discovered
> something which does _not_ support unsigned long long --- the "sparse"
> tool. :-(
Yes, this problem has been reported by Fengguang. So I am plan to use
another method to define extent_status structure as last time we
discuessed. What do you think?
Thanks,
- Zheng
>
> I discovered this when running "make C=1", i.e.:
>
> rm -f fs/ext4/extents_status.o
> make C=1 fs/ext4/extents_status.o
>
> Here's a simple test case which demo's that sparse doesn't deal well
> with unsigned long long. If we change the last two fields in struct
> extents_status to:
>
> unsigned long es_pblk : 30; /* first physical block */
> unsigned long es_status : 2; /* record the status of extent */
>
> sparse doesn't complain. But as shown below, sparse complains bitterly:
>
> /tmp/foo.c:22:24: warning: invalid access past the end of 'es' (24 28)
>
> I'm not sure Chris will consider this a bug, since bitfields
> with "unsigned long long" isn't standards complaint, even if gcc and
> clang supports it. Chris, what do you think?
>
> - Ted
>
>
> #!/bin/sh
> cat > /tmp/foo.c << EOF
> #include <unistd.h>
> #include <stdio.h>
>
> struct rb_node {
> unsigned long __rb_parent_color;
> struct rb_node *rb_right;
> struct rb_node *rb_left;
> } __attribute__((aligned(sizeof(long))));
>
> struct extent_status {
> struct rb_node rb_node;
> unsigned long es_lblk; /* first logical block extent covers */
> unsigned long es_len; /* length of extent in block */
> unsigned long long es_pblk : 62; /* first physical block */
> unsigned long long es_status : 2; /* record the status of extent */
> };
>
> int main(int argc, char **argv)
> {
> struct extent_status es;
>
> es.es_status = 3;
>
> printf("%d\n", es.es_status);
> printf("size %u\n", sizeof(es));
> }
> EOF
> sparse /tmp/foo.c
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