Em Wed, Nov 11, 2015 at 10:05:19PM +0100, David Sterba escreveu:
> On Wed, Nov 11, 2015 at 05:11:51PM -0300, Arnaldo Carvalho de Melo wrote:
> > > struct btrfs_path {
> ...
> > > u8 reada; /* 128 1 */
> > > u8 lowest_level; /* 129 1 */
> ...
> > > };
...
> > int reada; /* 128 4 */
> > int lowest_level; /* 132 4 */
> > unsigned int search_for_split:1; /* 136:31 4 */
> > unsigned int keep_locks:1; /* 136:30 4 */
...
> > Ok, but then 'reada' and 'lowest_level' are both int in my file, lemme try
> > converting it and rebuilding...
> Yes, they're both 'int' in current git versions, I'm trying to reduce
> size of the structure and using pahole to see the result. When both
> members were switched to u8 the warning appeared. Sorry for confusion.
So, I did the change and got the same BFA, with:
gcc version 4.9.2 20150212 (Red Hat 4.9.2-6) (GCC)
I'm trying to figure out how this can make sense:
u8 reada; /* 128 1 */
u8 lowest_level; /* 129 1 */
/* Bitfield combined with previous fields */
unsigned int search_for_split:1; /* 128:15 4 */
unsigned int keep_locks:1; /* 128:14 4 */
unsigned int skip_locking:1; /* 128:13 4 */
unsigned int leave_spinning:1; /* 128:12 4 */
unsigned int search_commit_root:1; /* 128:11 4 */
unsigned int need_commit_sem:1; /* 128:10 4 */
unsigned int skip_release_on_error:1; /* 128: 9 4 */
I.e. it is like skip_release_on_error uses the first bit of 'lowest_level',
i.e. the ninth bit starting at byte offset 128... I was expecting it to be:
u8 reada; /* 128 1 */
u8 lowest_level; /* 129 1 */
/* Bitfield combined with previous fields */
unsigned int search_for_split:1; /* 128:22 4 */
unsigned int keep_locks:1; /* 128:21 4 */
unsigned int skip_locking:1; /* 128:20 4 */
unsigned int leave_spinning:1; /* 128:19 4 */
unsigned int search_commit_root:1; /* 128:18 4 */
unsigned int need_commit_sem:1; /* 128:17 4 */
unsigned int skip_release_on_error:1; /* 128:16 4 */
Because by combining the bitfield with the two u8 before it, it would read as:
unsigned int reada:8; /* 128:0 4 */
unsigned int lowest_level:8; /* 128:8 4 */
:-\
Looking at the readelf output now...
- Arnaldo
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