Em Wed, Nov 11, 2015 at 07:13:40PM -0300, Arnaldo Carvalho de Melo escreveu:
> 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...
So, it seems to be a BFA, but on gcc's part, I'll try to cook a test...
<2><10cb7>: Abbrev Number: 34 (DW_TAG_member)
<10cb8> DW_AT_name : (indirect string, offset: 0x10d67): reada
<10cbf> DW_AT_type : <0xad>
<10cc3> DW_AT_data_member_location: 128
<2><10cc4>: Abbrev Number: 34 (DW_TAG_member)
<10cc5> DW_AT_name : (indirect string, offset: 0xfbc0): lowest_level
<10ccc> DW_AT_type : <0xad>
<10cd0> DW_AT_data_member_location: 129
<2><10cd1>: Abbrev Number: 55 (DW_TAG_member)
<10cd2> DW_AT_name : (indirect string, offset: 0xff9a): search_for_split
<10cd9> DW_AT_type : <0x78>
<10cdd> DW_AT_byte_size : 4
<10cde> DW_AT_bit_size : 1
<10cdf> DW_AT_bit_offset : 15
<10ce0> DW_AT_data_member_location: 128
<2><10ce1>: Abbrev Number: 55 (DW_TAG_member)
<10ce2> DW_AT_name : (indirect string, offset: 0x7278): keep_locks
<10ce9> DW_AT_type : <0x78>
<10ced> DW_AT_byte_size : 4
<10cee> DW_AT_bit_size : 1
<10cef> DW_AT_bit_offset : 14
<10cf0> DW_AT_data_member_location: 128
<2><10cf1>: Abbrev Number: 55 (DW_TAG_member)
<10cf2> DW_AT_name : (indirect string, offset: 0x8d9a): skip_locking
<10cf9> DW_AT_type : <0x78>
<10cfd> DW_AT_byte_size : 4
<10cfe> DW_AT_bit_size : 1
<10cff> DW_AT_bit_offset : 13
<10d00> DW_AT_data_member_location: 128
<2><10d01>: Abbrev Number: 55 (DW_TAG_member)
<10d02> DW_AT_name : (indirect string, offset: 0x1297b): leave_spinning
<10d09> DW_AT_type : <0x78>
<10d0d> DW_AT_byte_size : 4
<10d0e> DW_AT_bit_size : 1
<10d0f> DW_AT_bit_offset : 12
<10d10> DW_AT_data_member_location: 128
<2><10d11>: Abbrev Number: 55 (DW_TAG_member)
<10d12> DW_AT_name : (indirect string, offset: 0x1837): search_commit_root
<10d19> DW_AT_type : <0x78>
<10d1d> DW_AT_byte_size : 4
<10d1e> DW_AT_bit_size : 1
<10d1f> DW_AT_bit_offset : 11
<10d20> DW_AT_data_member_location: 128
<2><10d21>: Abbrev Number: 55 (DW_TAG_member)
<10d22> DW_AT_name : (indirect string, offset: 0x1205c): need_commit_sem
<10d29> DW_AT_type : <0x78>
<10d2d> DW_AT_byte_size : 4
<10d2e> DW_AT_bit_size : 1
<10d2f> DW_AT_bit_offset : 10
<10d30> DW_AT_data_member_location: 128
<2><10d31>: Abbrev Number: 55 (DW_TAG_member)
<10d32> DW_AT_name : (indirect string, offset: 0xcc1e): skip_release_on_error
<10d39> DW_AT_type : <0x78>
<10d3d> DW_AT_byte_size : 4
<10d3e> DW_AT_bit_size : 1
<10d3f> DW_AT_bit_offset : 9
<10d40> DW_AT_data_member_location: 128
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