On 1/10/19 3:03 PM, Andrii Nakryiko wrote:
> On Thu, Jan 10, 2019 at 10:10 AM Arnaldo Carvalho de Melo
> <acme@xxxxxxxxxx> wrote:
>>
>> Em Thu, Jan 10, 2019 at 02:50:32PM -0300, Arnaldo Carvalho de Melo escreveu:
>>> So, the size for an enumeration in BTF is in bytes, not in bits, as in
>>> CTF, fixed with the patch below, looking at the other cases now.
>>
>> We're down to packed data structs, probably in the BTF encoder, see
>> below.
>>
>> $ diff -u /tmp/tcp.o.dwarf.c /tmp/tcp.o.btf.c
>> --- /tmp/tcp.o.dwarf.c 2019-01-10 12:10:26.890521322 -0300
>> +++ /tmp/tcp.o.btf.c 2019-01-10 14:46:04.584743337 -0300
>> @@ -585,11 +585,17 @@
>> __u16 vesapm_off; /* 48 2 */
>> __u16 pages; /* 50 2 */
>> __u16 vesa_attributes; /* 52 2 */
>> - __u32 capabilities; /* 54 4 */
>> - __u32 ext_lfb_base; /* 58 4 */
>> + __u32 capabilities; /* 52 4 */
>> + __u32 ext_lfb_base; /* 56 4 */
>> +
>> + /* XXX 2 bytes hole, try to pack */
>> +
>> __u8 _reserved[2]; /* 62 2 */
>>
>> Were these 4 extra bytes came from? The original struct is:
>>
>> /*
>> * These are set up by the setup-routine at boot-time:
>> */
>>
>> struct screen_info {
>> __u8 orig_x; /* 0x00 */
>> __u8 orig_y; /* 0x01 */
>> __u16 ext_mem_k; /* 0x02 */
>> __u16 orig_video_page; /* 0x04 */
>> __u8 orig_video_mode; /* 0x06 */
>> __u8 orig_video_cols; /* 0x07 */
>> __u8 flags; /* 0x08 */
>> __u8 unused2; /* 0x09 */
>> __u16 orig_video_ega_bx;/* 0x0a */
>> __u16 unused3; /* 0x0c */
>> __u8 orig_video_lines; /* 0x0e */
>> __u8 orig_video_isVGA; /* 0x0f */
>> __u16 orig_video_points;/* 0x10 */
>>
>> /* VESA graphic mode -- linear frame buffer */
>> __u16 lfb_width; /* 0x12 */
>> __u16 lfb_height; /* 0x14 */
>> __u16 lfb_depth; /* 0x16 */
>> __u32 lfb_base; /* 0x18 */
>> __u32 lfb_size; /* 0x1c */
>> __u16 cl_magic, cl_offset; /* 0x20 */
>> __u16 lfb_linelength; /* 0x24 */
>> __u8 red_size; /* 0x26 */
>> __u8 red_pos; /* 0x27 */
>> __u8 green_size; /* 0x28 */
>> __u8 green_pos; /* 0x29 */
>> __u8 blue_size; /* 0x2a */
>> __u8 blue_pos; /* 0x2b */
>> __u8 rsvd_size; /* 0x2c */
>> __u8 rsvd_pos; /* 0x2d */
>> __u16 vesapm_seg; /* 0x2e */
>> __u16 vesapm_off; /* 0x30 */
>> __u16 pages; /* 0x32 */
>> __u16 vesa_attributes; /* 0x34 */
>> __u32 capabilities; /* 0x36 */
>> __u32 ext_lfb_base; /* 0x3a */
>> __u8 _reserved[2]; /* 0x3e */
>> } __attribute__((packed));
>>
>> $ pahole --hex -F dwarf -C screen_info ~/git/build/v4.20-rc5/net/ipv4/tcp.o
>> struct screen_info {
>> __u8 orig_x; /* 0 0x1 */
>> __u8 orig_y; /* 0x1 0x1 */
>> __u16 ext_mem_k; /* 0x2 0x2 */
>> __u16 orig_video_page; /* 0x4 0x2 */
>> __u8 orig_video_mode; /* 0x6 0x1 */
>> __u8 orig_video_cols; /* 0x7 0x1 */
>> __u8 flags; /* 0x8 0x1 */
>> __u8 unused2; /* 0x9 0x1 */
>> __u16 orig_video_ega_bx; /* 0xa 0x2 */
>> __u16 unused3; /* 0xc 0x2 */
>> __u8 orig_video_lines; /* 0xe 0x1 */
>> __u8 orig_video_isVGA; /* 0xf 0x1 */
>> __u16 orig_video_points; /* 0x10 0x2 */
>> __u16 lfb_width; /* 0x12 0x2 */
>> __u16 lfb_height; /* 0x14 0x2 */
>> __u16 lfb_depth; /* 0x16 0x2 */
>> __u32 lfb_base; /* 0x18 0x4 */
>> __u32 lfb_size; /* 0x1c 0x4 */
>> __u16 cl_magic; /* 0x20 0x2 */
>> __u16 cl_offset; /* 0x22 0x2 */
>> __u16 lfb_linelength; /* 0x24 0x2 */
>> __u8 red_size; /* 0x26 0x1 */
>> __u8 red_pos; /* 0x27 0x1 */
>> __u8 green_size; /* 0x28 0x1 */
>> __u8 green_pos; /* 0x29 0x1 */
>> __u8 blue_size; /* 0x2a 0x1 */
>> __u8 blue_pos; /* 0x2b 0x1 */
>> __u8 rsvd_size; /* 0x2c 0x1 */
>> __u8 rsvd_pos; /* 0x2d 0x1 */
>> __u16 vesapm_seg; /* 0x2e 0x2 */
>> __u16 vesapm_off; /* 0x30 0x2 */
>> __u16 pages; /* 0x32 0x2 */
>> __u16 vesa_attributes; /* 0x34 0x2 */
>> __u32 capabilities; /* 0x36 0x4 */
>> __u32 ext_lfb_base; /* 0x3a 0x4 */
>> __u8 _reserved[2]; /* 0x3e 0x2 */
>>
>> /* size: 64, cachelines: 1, members: 36 */
>> };
>>
>> the dwarf loader/pahole printer seem to be doing the right thing, the
>> BTF encoder, it seems, has issues with attribute((packed)) structs, see
>> below.
>>
>> [acme@quaco pahole]$ pahole --hex -F dwarf -C screen_info ~/git/build/v4.20-rc5/net/ipv4/tcp.o > /tmp/dwarf
>> [acme@quaco pahole]$ pahole --hex -F btf -C screen_info ~/git/build/v4.20-rc5/net/ipv4/tcp.o > /tmp/btf
>> [acme@quaco pahole]$ diff -u /tmp/dwarf /tmp/btf
>> --- /tmp/dwarf 2019-01-10 15:00:14.946723885 -0300
>> +++ /tmp/btf 2019-01-10 15:00:18.669757798 -0300
>> @@ -32,9 +32,15 @@
>> __u16 vesapm_off; /* 0x30 0x2 */
>> __u16 pages; /* 0x32 0x2 */
>> __u16 vesa_attributes; /* 0x34 0x2 */
>> - __u32 capabilities; /* 0x36 0x4 */
>> + __u32 capabilities; /* 0x34 0x4 */
>> - __u32 ext_lfb_base; /* 0x3a 0x4 */
>> + __u32 ext_lfb_base; /* 0x38 0x4 */
>> +
>> + /* XXX 2 bytes hole, try to pack */
>> +
>> __u8 _reserved[2]; /* 0x3e 0x2 */
>>
>> /* size: 64, cachelines: 1, members: 36 */
>> + /* sum members: 60, holes: 1, sum holes: 2 */
>> +
>> + /* BRAIN FART ALERT! 64 != 60 + 2(holes), diff = 2 */
>> };
>> [acme@quaco pahole]$
>>
>> Why the BTF encoder or loader is getting this in the wrong place...
>> Debugging...
>>
>> /* size: 64, cachelines: 1, members: 36 */
>> + /* sum members: 60, holes: 1, sum holes: 2 */
>> +
>> + /* BRAIN FART ALERT! 64 != 60 + 2(holes), diff = 2 */
>> };
>> struct apm_bios_info {
>> __u16 version; /* 0 2 */
>> @@ -630,7 +636,10 @@
>> __u32 sectors_per_track; /* 12 4 */
>> __u64 number_of_sectors; /* 16 8 */
>> __u16 bytes_per_sector; /* 24 2 */
>> - __u32 dpte_ptr; /* 26 4 */
>> + __u32 dpte_ptr; /* 24 4 */
>>
>>
>> Looks like the same problem as with screen_info, 'dpte_ptr' got
>> "unionized" with 'bytes_per_sector'
>>
>> +
>> + /* XXX 2 bytes hole, try to pack */
>> +
>> __u16 key; /* 30 2 */
>> __u8 device_path_info_length; /* 32 1 */
>> __u8 reserved2; /* 33 1 */
>> @@ -683,7 +692,10 @@
>> } atapi; /* 56 16 */
>> struct {
>> __u16 id; /* 56 2 */
>> - __u64 lun; /* 58 8 */
>> + __u64 lun; /* 56 8 */
>>
>> Ditto, here it could be trying to put 'lun' in its natural alignment,
>> probably 'struct edd_device_params' is packed like screen_info? Yes...
>> include/uapi/linux/edd.h line 72
>>
>> +
>> + /* XXX 2 bytes hole, try to pack */
>> +
>> /* --- cacheline 1 boundary (64 bytes) was 2 bytes ago --- */
>> __u16 reserved1; /* 66 2 */
>> __u32 reserved2; /* 68 4 */
>> @@ -733,7 +745,10 @@
>> __u8 checksum; /* 73 1 */
>>
>> /* size: 74, cachelines: 2, members: 18 */
>> + /* sum members: 70, holes: 1, sum holes: 2 */
>> /* last cacheline: 10 bytes */
>> +
>> + /* BRAIN FART ALERT! 74 != 70 + 2(holes), diff = 2 */
>> };
>> struct edd_info {
>> __u8 device; /* 0 1 */
>> @@ -849,10 +864,13 @@
>> };
>> struct desc_ptr {
>> short unsigned int size; /* 0 2 */
>> - long unsigned int address; /* 2 8 */
>> + long unsigned int address; /* 0 8 */
>>
>> One more packed struct:
>>
>> struct desc_ptr {
>> unsigned short size;
>> unsigned long address;
>> } __attribute__((packed)) ;
>>
>> /* size: 10, cachelines: 1, members: 2 */
>> + /* padding: 2 */
>> /* last cacheline: 10 bytes */
>> +
>> + /* BRAIN FART ALERT! 10 != 2 + 0(holes), diff = 8 */
>> };
>> struct pgprot {
>> pgprotval_t pgprot; /* 0 8 */
>> @@ -1467,10 +1485,13 @@
>> };
>> struct x86_hw_tss {
>>
>> Also a packed struct
>>
>> u32 reserved1; /* 0 4 */
>> - u64 sp0; /* 4 8 */
>> - u64 sp1; /* 12 8 */
>> - u64 sp2; /* 20 8 */
>> - u64 reserved2; /* 28 8 */
>> + u64 sp0; /* 0 8 */
>> + u64 sp1; /* 8 8 */
>> + u64 sp2; /* 16 8 */
>> + u64 reserved2; /* 24 8 */
>> +
>> + /* XXX 4 bytes hole, try to pack */
>> +
>> u64 ist[7]; /* 36 56 */
>> /* --- cacheline 1 boundary (64 bytes) was 28 bytes ago --- */
>> u32 reserved3; /* 92 4 */
>> @@ -1479,7 +1500,10 @@
>> u16 io_bitmap_base; /* 102 2 */
>>
>> /* size: 104, cachelines: 2, members: 10 */
>> + /* sum members: 96, holes: 1, sum holes: 4 */
>> /* last cacheline: 40 bytes */
>> +
>> + /* BRAIN FART ALERT! 104 != 96 + 4(holes), diff = 4 */
>> };
>> struct seq_operations {
>> void * (*start)(struct seq_file *, loff_t *); /* 0 8 */
>>
>>
>> This last one is interesting, was this done on purpose? I think one
>> level of indirection more and we would keep the original expressiveness.
>>
>> @@ -8473,7 +8497,7 @@
>> struct lruvec_stat * lruvec_stat_cpu; /* 136 8 */
>> atomic_long_t lruvec_stat[30]; /* 144 240 */
>> /* --- cacheline 6 boundary (384 bytes) --- */
>> - long unsigned int lru_zone_size[5][5]; /* 384 200 */
>> + long unsigned int lru_zone_size[25]; /* 384 200 */
>> /* --- cacheline 9 boundary (576 bytes) was 8 bytes ago --- */
>> struct mem_cgroup_reclaim_iter iter[13]; /* 584 208 */
>> /* --- cacheline 12 boundary (768 bytes) was 24 bytes ago --- */
>>
>> - Arnaldo
>
> There appears to be problems with bitfields in both DWARF data and
> pahole's conversion from DWARF to BTF (see test file source code and
> pahole output at the bottom).
>
> 1. pahole believes unpacked.y1 has offset 7, which is incorrect
> (should be 32?).
> unpacked.y2 has offset 32, which also doesn't make sense.
> DWARF info for unpacked.y1 and unpacked.y2 also seem wrong (how
> do we get offset 18 for y1?).
>
> <2><63>: Abbrev Number: 3 (DW_TAG_member)
> <64> DW_AT_name : y1
> <67> DW_AT_decl_file : 1
> <68> DW_AT_decl_line : 5
> <69> DW_AT_type : <0x87>
> <6d> DW_AT_byte_size : 4
> <6e> DW_AT_bit_size : 7
> <6f> DW_AT_bit_offset : 18
> <70> DW_AT_data_member_location: 0
> <2><71>: Abbrev Number: 3 (DW_TAG_member)
> <72> DW_AT_name : y2
> <75> DW_AT_decl_file : 1
> <76> DW_AT_decl_line : 6
> <77> DW_AT_type : <0x87>
> <7b> DW_AT_byte_size : 4
> <7c> DW_AT_bit_size : 20
> <7d> DW_AT_bit_offset : 12
> <7e> DW_AT_data_member_location: 4
>
>
> 2. Similar problems with packed.y1 and packed.y2. packed.y2 offset
> is negative value even in DWARF:
>
> <2><d2>: Abbrev Number: 6 (DW_TAG_member)
> <d3> DW_AT_name : y2
> <d6> DW_AT_decl_file : 1
> <d7> DW_AT_decl_line : 14
> <d8> DW_AT_type : <0x87>
> <dc> DW_AT_byte_size : 4
> <dd> DW_AT_bit_size : 20
> <de> DW_AT_bit_offset : -2
> <df> DW_AT_data_member_location: 0
Did some research on why we got -2 as bit_offset with the above packed
data structure.
First, the compiler generates correct thing. the negative
DW_AT_bit_offset is allowed for dwarf2, but not dwarf4.
The "-2" here means (1). the member is crossing two
adjacent "4" bytes boundary (DW_AT_byte_size = 4), and
(2). the -2 means the the starting bit is at the "4" byte boundary - 2
bits. So basically it covers:
| |
V V
[0 1 .....30 31][0 .. 17 18 ... 31]
totally 20 bits.
The following patch fixed the issue:
-bash-4.4$ git diff
diff --git a/dwarves.h b/dwarves.h
index e6bffe8..e5f8347 100644
--- a/dwarves.h
+++ b/dwarves.h
@@ -831,7 +831,7 @@ struct class_member {
uint32_t bit_size;
uint32_t byte_offset;
size_t byte_size;
- uint8_t bitfield_offset;
+ int8_t bitfield_offset;
uint8_t bitfield_size;
uint8_t bit_hole;
uint8_t bitfield_end:1;
-bash-4.4$
With the above change:
-bash-4.4$ ~/work/github/pahole/build/pahole -JV bitfields.o
File bitfields.o:
[1] INT int size=4 bit_offset=0 nr_bits=32 encoding=SIGNED
[2] STRUCT packed kind_flag=1 size=5 vlen=5
x1 type_id=3 bitfield_size=1 bits_offset=0
x2 type_id=3 bitfield_size=3 bits_offset=1
x3 type_id=3 bitfield_size=3 bits_offset=4
y1 type_id=1 bitfield_size=7 bits_offset=7
y2 type_id=1 bitfield_size=20 bits_offset=14
[3] INT char size=1 bit_offset=0 nr_bits=8 encoding=(none)
[4] STRUCT unpacked kind_flag=1 size=8 vlen=5
x1 type_id=3 bitfield_size=1 bits_offset=0
x2 type_id=3 bitfield_size=3 bits_offset=1
x3 type_id=3 bitfield_size=3 bits_offset=4
y1 type_id=1 bitfield_size=7 bits_offset=7
y2 type_id=1 bitfield_size=20 bits_offset=32
[5] UNION packed_union kind_flag=0 size=8 vlen=4
x1 type_id=3 bits_offset=0
y2 type_id=1 bits_offset=0
s1 type_id=2 bits_offset=0
s2 type_id=4 bits_offset=0
[6] UNION unpacked_union kind_flag=0 size=8 vlen=3
x1 type_id=3 bits_offset=0
y2 type_id=1 bits_offset=0
s type_id=4 bits_offset=0
-bash-4.4$
Will send out a patch shortly.
>
> andriin@devvm$ cat bitfields.c
> struct unpacked{
> char x1: 1;
> char x2: 3;
> char x3: 3;
> int y1: 7;
> int y2: 20;
> };
>
> struct packed{
> char x1: 1;
> char x2: 3;
> char x3: 3;
> int y1: 7;
> int y2: 20;
> } __attribute__((packed));
>
> union packed_union {
> char x1;
> int y2;
> struct packed s1;
> struct unpacked s2;
> };
>
> union unpacked_union {
> char x1;
> int y2;
> struct unpacked s;
> } __attribute__((packed));
>
> int main() {
> struct packed s1;
> struct unpacked s2;
> union packed_union u1;
> union unpacked_union u2;
> return 0;
> }
> andriin@devvm$ cc -g bitfields.c -o bitfields
> andriin@devvm$ LLVM_OBJCOPY=objcopy ~/local/pahole/build/pahole -JV bitfields
> File bitfields:
> [1] STRUCT unpacked kind_flag=1 size=8 vlen=5
> x1 type_id=2 bitfield_size=1 bits_offset=0
> x2 type_id=2 bitfield_size=3 bits_offset=1
> x3 type_id=2 bitfield_size=3 bits_offset=4
> y1 type_id=3 bitfield_size=7 bits_offset=7
> y2 type_id=3 bitfield_size=20 bits_offset=32
> [2] INT char size=1 bit_offset=0 nr_bits=8 encoding=(none)
> [3] INT int size=4 bit_offset=0 nr_bits=32 encoding=SIGNED
> [4] STRUCT packed kind_flag=1 size=5 vlen=5
> x1 type_id=2 bitfield_size=1 bits_offset=0
> x2 type_id=2 bitfield_size=3 bits_offset=1
> x3 type_id=2 bitfield_size=3 bits_offset=4
> y1 type_id=3 bitfield_size=7 bits_offset=7
> y2 type_id=3 bitfield_size=255 bits_offset=16776974
> [5] UNION packed_union kind_flag=0 size=8 vlen=4
> x1 type_id=2 bits_offset=0
> y2 type_id=3 bits_offset=0
> s1 type_id=4 bits_offset=0
> s2 type_id=1 bits_offset=0
> [6] UNION unpacked_union kind_flag=0 size=8 vlen=3
> x1 type_id=2 bits_offset=0
> y2 type_id=3 bits_offset=0
> s type_id=1 bits_offset=0
> andriin@devvm$ readelf -wi bitfields
> Contents of the .debug_info section:
>
> ...
>
> <1><2d>: Abbrev Number: 2 (DW_TAG_structure_type)
> <2e> DW_AT_name : (indirect string, offset: 0x4e): unpacked
> <32> DW_AT_byte_size : 8
> <33> DW_AT_decl_file : 1
> <34> DW_AT_decl_line : 1
> <35> DW_AT_sibling : <0x80>
> <2><39>: Abbrev Number: 3 (DW_TAG_member)
> <3a> DW_AT_name : x1
> <3d> DW_AT_decl_file : 1
> <3e> DW_AT_decl_line : 2
> <3f> DW_AT_type : <0x80>
> <43> DW_AT_byte_size : 1
> <44> DW_AT_bit_size : 1
> <45> DW_AT_bit_offset : 7
> <46> DW_AT_data_member_location: 0
> <2><47>: Abbrev Number: 3 (DW_TAG_member)
> <48> DW_AT_name : x2
> <4b> DW_AT_decl_file : 1
> <4c> DW_AT_decl_line : 3
> <4d> DW_AT_type : <0x80>
> <51> DW_AT_byte_size : 1
> <52> DW_AT_bit_size : 3
> <53> DW_AT_bit_offset : 4
> <54> DW_AT_data_member_location: 0
> <2><55>: Abbrev Number: 3 (DW_TAG_member)
> <56> DW_AT_name : x3
> <59> DW_AT_decl_file : 1
> <5a> DW_AT_decl_line : 4
> <5b> DW_AT_type : <0x80>
> <5f> DW_AT_byte_size : 1
> <60> DW_AT_bit_size : 3
> <61> DW_AT_bit_offset : 1
> <62> DW_AT_data_member_location: 0
> <2><63>: Abbrev Number: 3 (DW_TAG_member)
> <64> DW_AT_name : y1
> <67> DW_AT_decl_file : 1
> <68> DW_AT_decl_line : 5
> <69> DW_AT_type : <0x87>
> <6d> DW_AT_byte_size : 4
> <6e> DW_AT_bit_size : 7
> <6f> DW_AT_bit_offset : 18
> <70> DW_AT_data_member_location: 0
> <2><71>: Abbrev Number: 3 (DW_TAG_member)
> <72> DW_AT_name : y2
> <75> DW_AT_decl_file : 1
> <76> DW_AT_decl_line : 6
> <77> DW_AT_type : <0x87>
> <7b> DW_AT_byte_size : 4
> <7c> DW_AT_bit_size : 20
> <7d> DW_AT_bit_offset : 12
> <7e> DW_AT_data_member_location: 4
> <2><7f>: Abbrev Number: 0
> <1><80>: Abbrev Number: 4 (DW_TAG_base_type)
> <81> DW_AT_byte_size : 1
> <82> DW_AT_encoding : 6 (signed char)
> <83> DW_AT_name : (indirect string, offset: 0xb3): char
> <1><87>: Abbrev Number: 5 (DW_TAG_base_type)
> <88> DW_AT_byte_size : 4
> <89> DW_AT_encoding : 5 (signed)
> <8a> DW_AT_name : int
> <1><8e>: Abbrev Number: 2 (DW_TAG_structure_type)
> <8f> DW_AT_name : (indirect string, offset: 0x50): packed
> <93> DW_AT_byte_size : 5
> <94> DW_AT_decl_file : 1
> <95> DW_AT_decl_line : 9
> <96> DW_AT_sibling : <0xe1>
> <2><9a>: Abbrev Number: 3 (DW_TAG_member)
> <9b> DW_AT_name : x1
> <9e> DW_AT_decl_file : 1
> <9f> DW_AT_decl_line : 10
> <a0> DW_AT_type : <0x80>
> <a4> DW_AT_byte_size : 1
> <a5> DW_AT_bit_size : 1
> <a6> DW_AT_bit_offset : 7
> <a7> DW_AT_data_member_location: 0
> <2><a8>: Abbrev Number: 3 (DW_TAG_member)
> <a9> DW_AT_name : x2
> <ac> DW_AT_decl_file : 1
> <ad> DW_AT_decl_line : 11
> <ae> DW_AT_type : <0x80>
> <b2> DW_AT_byte_size : 1
> <b3> DW_AT_bit_size : 3
> <b4> DW_AT_bit_offset : 4
> <b5> DW_AT_data_member_location: 0
> <2><b6>: Abbrev Number: 3 (DW_TAG_member)
> <b7> DW_AT_name : x3
> <ba> DW_AT_decl_file : 1
> <bb> DW_AT_decl_line : 12
> <bc> DW_AT_type : <0x80>
> <c0> DW_AT_byte_size : 1
> <c1> DW_AT_bit_size : 3
> <c2> DW_AT_bit_offset : 1
> <c3> DW_AT_data_member_location: 0
> <2><c4>: Abbrev Number: 3 (DW_TAG_member)
> <c5> DW_AT_name : y1
> <c8> DW_AT_decl_file : 1
> <c9> DW_AT_decl_line : 13
> <ca> DW_AT_type : <0x87>
> <ce> DW_AT_byte_size : 4
> <cf> DW_AT_bit_size : 7
> <d0> DW_AT_bit_offset : 18
> <d1> DW_AT_data_member_location: 0
> <2><d2>: Abbrev Number: 6 (DW_TAG_member)
> <d3> DW_AT_name : y2
> <d6> DW_AT_decl_file : 1
> <d7> DW_AT_decl_line : 14
> <d8> DW_AT_type : <0x87>
> <dc> DW_AT_byte_size : 4
> <dd> DW_AT_bit_size : 20
> <de> DW_AT_bit_offset : -2
> <df> DW_AT_data_member_location: 0
> <2><e0>: Abbrev Number: 0
>
> ...
>
