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. :-(
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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