Em Mon, Jan 14, 2019 at 10:06:11PM +0000, Yonghong Song escreveu:
> On 1/14/19 10:13 AM, Arnaldo Carvalho de Melo wrote:
> > Em Mon, Jan 14, 2019 at 04:55:42PM +0000, Yonghong Song escreveu:
> >> On 1/14/19 6:27 AM, Arnaldo Carvalho de Melo wrote:
> > Which ends up producing this output, that still has stuff to do wrt the
> > hole/padding calculations, but has the offset adjusted to that '30'
> > value instead of showing -1:
> >
> > [acme@quaco pahole]$ pahole examples/yonghong/packed_bitfield.o
> > struct packed {
> > char x1:1; /* 0: 7 1 */
> > char x2:3; /* 0: 4 1 */
> > char x3:3; /* 0: 1 1 */
> > int y1:7; /* 0:18 4 */
> > int y2:20; /* 0:30 4 */
>
> The y2 should be "4:30"?
So, I kept that patch and added another hunk, the first one here:
diff --git a/dwarves_fprintf.c b/dwarves_fprintf.c
index bd46f97916fc..39f96318625e 100644
--- a/dwarves_fprintf.c
+++ b/dwarves_fprintf.c
@@ -753,6 +753,9 @@ static size_t class_member__fprintf(struct class_member *member, bool union_memb
sconf.base_offset = offset;
}
+ if (member->bitfield_offset < 0)
+ offset += member->byte_size;
+
if (!conf->suppress_comments)
printed_cacheline = class__fprintf_cacheline_boundary(conf, offset, fp);
@@ -807,9 +810,14 @@ static size_t class_member__fprintf(struct class_member *member, bool union_memb
offset);
if (member->bitfield_size != 0) {
+ unsigned int bitfield_offset = member->bitfield_offset;
+
+ if (member->bitfield_offset < 0)
+ bitfield_offset = member->byte_size * 8 + member->bitfield_offset;
+
printed += fprintf(fp, sconf.hex_fmt ?
":%#2x" : ":%2u",
- member->bitfield_offset);
+ bitfield_offset);
size_spacing -= 3;
}
With it we get what you suggested:
[acme@quaco pahole]$ pahole examples/yonghong/packed_bitfield.o
struct packed {
char x1:1; /* 0: 7 1 */
char x2:3; /* 0: 4 1 */
char x3:3; /* 0: 1 1 */
int y1:7; /* 0:18 4 */
int y2:20; /* 4:30 4 */
/* size: 5, cachelines: 1, members: 5 */
/* padding: 1 */
/* bit_padding: 254 bits */
/* last cacheline: 5 bytes */
/* BRAIN FART ALERT! 5 != 1 + 0(holes), diff = 4 */
};
[acme@quaco pahole]$
And, if I use a cross compiler to build a big endian .o:
[acme@quaco ~]$ dsh ubuntu:18.04-x-powerpc
perfbuilder@47aa4489b67f:/git/pahole$ powerpc-linux-gnu-gcc -O2 -g -c examples/yonghong/packed_bitfield.c -o /git/tmp/packed_bitfield.powerpc.o
perfbuilder@47aa4489b67f:/git/pahole$ exit
The one for x86_64:
[acme@quaco pahole]$ file examples/yonghong/packed_bitfield.o
examples/yonghong/packed_bitfield.o: ELF 64-bit LSB relocatable, x86-64, version 1 (SYSV), with debug_info, not stripped
For powerpc:
[acme@quaco pahole]$ file ~acme/git/tmp/packed_bitfield.powerpc.o
/home/acme/git/tmp/packed_bitfield.powerpc.o: ELF 32-bit MSB relocatable, PowerPC or cisco 4500, version 1 (SYSV), with debug_info, not stripped
[acme@quaco pahole]$
[acme@quaco pahole]$ pahole ~acme/git/tmp/packed_bitfield.powerpc.o
struct packed {
char x1:1; /* 0: 0 1 */
char x2:3; /* 0: 1 1 */
char x3:3; /* 0: 4 1 */
int y1:7; /* 0: 7 4 */
int y2:20; /* 0:14 4 */
/* size: 5, cachelines: 1, members: 5 */
/* padding: 1 */
/* bit_padding: 254 bits */
/* last cacheline: 5 bytes */
/* BRAIN FART ALERT! 5 != 1 + 0(holes), diff = 4 */
};
[acme@quaco pahole]$
And with sparc64:
[acme@quaco ~]$ dsh ubuntu:18.04-x-sparc64
perfbuilder@1ded5e9c526a:/git/pahole$ sparc64-linux-gnu-gcc -O2 -g -c examples/yonghong/packed_bitfield.c -o /git/tmp/packed_bitfield.sparc64.o
perfbuilder@1ded5e9c526a:/git/pahole$ exit
[acme@quaco pahole]$ file ~acme/git/tmp/packed_bitfield.sparc64.o
/home/acme/git/tmp/packed_bitfield.sparc64.o: ELF 64-bit MSB relocatable, SPARC V9, relaxed memory ordering, version 1 (SYSV), with debug_info, not stripped
[acme@quaco pahole]$ pahole ~acme/git/tmp/packed_bitfield.sparc64.o
struct packed {
char x1:1; /* 0: 0 1 */
char x2:3; /* 0: 1 1 */
char x3:3; /* 0: 4 1 */
int y1:7; /* 0: 7 4 */
int y2:20; /* 0:14 4 */
/* size: 5, cachelines: 1, members: 5 */
/* padding: 1 */
/* bit_padding: 254 bits */
/* last cacheline: 5 bytes */
/* BRAIN FART ALERT! 5 != 1 + 0(holes), diff = 4 */
};
[acme@quaco pahole]$
Seems to work?
Now need to tackle the holes calculations.
> This is how I interpret the above:
>
> > char x1:1; /* 0: 7 1 */
>
> ==> this will convert to big endian offset 0, size 1
> ==> offset = sizeof(char) - 7 - 1
>
> > char x2:3; /* 0: 4 1 */
> ===> this will convert to big endian offset 1, size 3
> ===> offset = sizeof(char) - 4 - 3
>
> > char x3:3; /* 0: 1 1 */
> ===> this will convert to big endian offset 4, size 3
> ===> offset = sizeof(char) - 1 - 3
>
> > int y1:7; /* 0:18 4 */
> ===> this will convert to big endian offset 7, size 7
> ===> offset = sizeof(int) - 18 - 7 = 7
> > int y2:20; /* 4:30 4 */
> ===> this will convert to big endian offset 14, size 20
> ===> offset = 4 * 8 + sizeof(int) - 30 - 20 = 14
>
>
> >
> > /* size: 5, cachelines: 1, members: 5 */
> > /* padding: 1 */
> > /* bit_padding: 254 bits */
> > /* last cacheline: 5 bytes */
> >
> > /* BRAIN FART ALERT! 5 != 1 + 0(holes), diff = 4 */
> > };
> > [acme@quaco pahole]$
> >
> > The following drawing _tries_ to paint this picture according to the
> > description you gave for negative bit_offsets, butthen it would be 8
> > bytes, the size of the struct is 5 bytes, sizeof(char) + sizeof(int),
> > and since the sum of the bit sizes is 34 bits, we need 5 bytes.
> >
> > x x
> > + 3 + + 2 + x1 +---- y2 ---+ +-- y2 --+
> > | | | | | | | | |
> > V V V V V V V V V
> > [0 1 2 3 4 5 6 7 ... 30 31][0 .. 17 18 ..... 24 .. 31]
>
> With packing, the elements layout may not be similar to the above.
>
> It probably likes below (I have a C program later):
>
> => memory increasing
> bits
> 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 ... 30 31 32 33 34 ...
> x1 | x2 | | x3 | | y1 | | y2 |
>
> In little representation, the following looks like the case:
> x1: byte0, bit 7
> x2: byte0, bit 4 - 6
> x3: byte0, bit 1 - 3
> y1: byte0, bit 0 and byte1, bit 2 - 7.
> y2: byte1, bit 0 - 1, and byte 2, 3, and byte4 6 -7.
>
> So there is no wasted bits. In the above your diagram, there are
> some wasted bits.
>
> I didn't check exactly how the little endian DW attributes are computed
> inside the compiler for the packed case. But one way to do it is
> - do a big endian bit offset/size assignment first. This should be
> straight forward.
> - convert to the little endian offset based on the corresponding
> field type and big endian field offset/type.
>
> -bash-4.4$ cat t2.c
> #include <stdio.h>
>
> struct packed {
> char x1: 1;
> char x2: 3;
> char x3: 3;
> int y1: 7;
> int y2: 20;
> } __attribute__((packed));
>
> int main() {
> struct packed p;
> int i;
>
> p.x1 = 1;
> p.x2 = 0;
> p.x3 = 2;
> p.y1 = 7 << 2;
> p.y2 = (1 << 18) + 3;
>
> for (i = 0; i < sizeof(p); i++)
> printf("i = %x\n", *(((unsigned char *)&p) + i));
>
> return 0;
> }
> -bash-4.4$ gcc t2.c
> -bash-4.4$ ./a.out
> i = 21
> i = ce
> i = 0
> i = 0
> i = fd
> -bash-4.4$
>
> >
> > Doesn't make sense, we don't have 64 bits, just 40.
> >
> > Can you hand hold me here? :-)
> >
> >>> seeing negative DW_AT_bit_offsets we should think it starts in this
> >>> location (0 in this case), but straddles to the next, so I should say
> >>> that it is at bit offset (DW_AT_byte_size * 8 - DW_AT_bit_offset), the
> >>> user, looking at this new pahole output will realize that it has 2 bits
> >>> at the end of the current DW_AT_data_member_location (0) but has 18 bits
> >>> in the next.
> >>>
> >>>
> >>>> (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
> >>>>>
> >>>>> ...
> >>>>>
> >>>
> >
--
- Arnaldo
