[Dwarf-Discuss] armcc DWARF
Michael Eager
eager@eagercon.com
Wed May 23 00:07:50 GMT 2018
On 05/22/2018 04:34 PM, David Anderson wrote:
> On 05/22/2018 04:18 PM, Michael Eager wrote:
>> On 05/22/2018 02:33 PM, David Anderson via Dwarf-Discuss wrote:
>>>
>>> I have been given a tiny object file? created by armcc
>>> using DWARF and things make no sense to me so far.
>>>
>>> dwarfdump (and libdwarf) use the SHT_GROUP section data to associate
>>> sections to their group.? This is a .o, not a fully linked executable or
>>> shared-library.
>>>
>>> (libdwarf assigns group numbers itself. group 1 is? non-dwo .debug
>>> sections)
>>> (any .dwo sections present would be shown as group 2
>>> if not listed in a section-group header, but no such are present here)
>>>
>>>
>> Can you post the output of readelf?
>>
> Section Headers:
> ? [Nr] Name????????????? Type??????????? Addr???? Off??? Size?? ES Flg
> Lk Inf Al
> ? [ 0]?????????????????? NULL??????????? 00000000 000000 000000 00
> 0?? 0? 0
> ? [ 1] .text???????????? PROGBITS??????? 00000000 000034 000008 00? AX
> 0?? 0? 4
> ? [ 2] .arm_vfe_header?? PROGBITS??????? 00000000 00003c 000004 00
> 0?? 0? 4
> ? [ 3] .comment????????? PROGBITS??????? 00000000 000040 00007a 00
> 0?? 0? 1
> ? [ 4] .debug_frame????? PROGBITS??????? 00000000 0000ba 000044 00
> 0?? 0? 1
> ? [ 5] .debug_info?????? PROGBITS??????? 00000000 0000fe 000098 00
> 0?? 0? 1
> ? [ 6] .debug_info?????? PROGBITS??????? 00000000 000196 0000e0 00
> ? [ 7] .debug_line?????? PROGBITS??????? 00000000 000276 00002c 00
> 0?? 0? 1
> ? [ 8] .debug_line?????? PROGBITS??????? 00000000 0002a2 000038 00
> 0?? 0? 1
> ? [ 9] .debug_loc??????? PROGBITS??????? 00000000 0002da 000050 00
> 0?? 0? 1
> ? [10] .debug_macinfo??? PROGBITS??????? 00000000 00032a 0002cc 00
> 0?? 0? 1
> ? [11] .debug_pubnames?? PROGBITS??????? 00000000 0005f6 000020 00
> 0?? 0? 1
> ? [12] __ARM_grp.a.h.2_sq0000_$0QbXG$5KW3_200000 GROUP
> 00000000 000618 00000c 04???? 23? 17? 4
> ? [13] .debug_info?????? PROGBITS??????? 00000000 000624 0000a8 00?? G
> 0?? 0? 1
> ? [14] .debug_line?????? PROGBITS??????? 00000000 0006cc 000028 00?? G
> 0?? 0? 1
> ? [15] __ARM_grp.b.h.2_ws0000_eYI6SD7WPJ9_500000 GROUP
> 00000000 0006f4 000008 04???? 23? 18? 4
> ? [16] .debug_info?????? PROGBITS??????? 00000000 0006fc 0000ac 00?? G
> 0?? 0? 1
> ? [17] __ARM_grp.test.c.2_cx0000_sjeCPPJ9rd8_900000 GROUP
> 00000000 0007a8 000010 04???? 23? 19? 4
> ? [18] .debug_info?????? PROGBITS??????? 00000000 0007b8 00009c 00?? G
> 0?? 0? 1
> ? [19] .debug_line?????? PROGBITS??????? 00000000 000854 000038 00?? G
> 0?? 0? 1
> ? [20] .debug_macinfo??? PROGBITS??????? 00000000 00088c 000010 00?? G
> 0?? 0? 1
> ? [21] __ARM_grp..debug_abbrev.group.2_Am0000_lbphKItke$2_000000
> GROUP?????????? 00000000 00089c 000008 04???? 23? 13? 4
> ? [22] .debug_abbrev???? PROGBITS??????? 00000000 0008a4 0005a4 00?? G
> 0?? 0? 1
> ? [23] .symtab?????????? SYMTAB????????? 00000000 000e48 000190 10
> 33? 13? 4
> ? [24] .rel.debug_frame? REL???????????? 00000000 000fd8 000010 08
> 23?? 4? 4
> ? [25] .rel.debug_info?? REL???????????? 00000000 000fe8 000018 08
> 23?? 5? 4
> ? [26] .rel.debug_info?? REL???????????? 00000000 001000 000068 08
> 23?? 6? 4
> ? [27] .rel.debug_line?? REL???????????? 00000000 001068 000008 08
> 23?? 8? 4
> ? [28] .rel.debug_pubnames REL???????????? 00000000 001070 000008 08
> 23? 11? 4
> ? [29] .rel.debug_info?? REL???????????? 00000000 001078 000010 08
> 23? 13? 4
> ? [30] .rel.debug_info?? REL???????????? 00000000 001088 000018 08
> 23? 16? 4
> ? [31] .rel.debug_info?? REL???????????? 00000000 0010a0 000020 08
> 23? 18? 4
> ? [32] .shstrtab???????? STRTAB????????? 00000000 0010c0 000172 00
> 0?? 0? 1
> ? [33] .strtab?????????? STRTAB????????? 00000000 001232 00037e 00
> 0?? 0? 1
> ? [34] .ARM.attributes?? ARM_ATTRIBUTES? 00000000 0015b0 000045 00
> 0?? 0? 1
>
>
> I'll email you? the test case object file, Mike, so you can see the
> group records etc.
>
> Here is the test source:
> #include "a.h"
> #include "b.h"
>
> void set_point(struct POINT *point, NUMBER x, NUMBER y)
> {
> ??? point->x = x;
> ??? point->y = y;
> }
>
>
> q3 1708: cat a.h
> typedef float NUMBER;
> q3 1709: cat b.h
> struct POINT {
> ??? NUMBER x;
> ??? NUMBER y;
> };
I compiled the test with ARM-GCC. Here is what it generates:
Section Headers:
[Nr] Name Type Addr Off Size ES Flg
Lk Inf Al
[ 0] NULL 00000000 000000 000000 00
0 0 0
[ 1] .text PROGBITS 00000000 000034 000040 00 AX
0 0 4
[ 2] .rel.text REL 00000000 000440 000008 08 I
17 1 4
[ 3] .data PROGBITS 00000000 000074 000000 00 WA
0 0 1
[ 4] .bss NOBITS 00000000 000074 000000 00 WA
0 0 1
[ 5] .debug_info PROGBITS 00000000 000074 0000a3 00
0 0 1
[ 6] .rel.debug_info REL 00000000 000448 000060 08 I
17 5 4
[ 7] .debug_abbrev PROGBITS 00000000 000117 000097 00
0 0 1
[ 8] .debug_aranges PROGBITS 00000000 0001ae 000020 00
0 0 1
[ 9] .rel.debug_arange REL 00000000 0004a8 000010 08 I
17 8 4
[10] .debug_line PROGBITS 00000000 0001ce 00004b 00
0 0 1
[11] .rel.debug_line REL 00000000 0004b8 000008 08 I
17 10 4
[12] .debug_str PROGBITS 00000000 000219 000090 01 MS
0 0 1
[13] .comment PROGBITS 00000000 0002a9 000031 01 MS
0 0 1
[14] .debug_frame PROGBITS 00000000 0002dc 000030 00
0 0 4
[15] .rel.debug_frame REL 00000000 0004c0 000010 08 I
17 14 4
[16] .ARM.attributes ARM_ATTRIBUTES 00000000 00030c 00002a 00
0 0 1
[17] .symtab SYMTAB 00000000 000338 0000f0 10
18 14 4
[18] .strtab STRTAB 00000000 000428 000015 00
0 0 1
[19] .shstrtab STRTAB 00000000 0004d0 0000a6 00
0 0 1
One, and only one, .debug_info, .debug_line, etc.
If the .debug_info section is generated in multiple pieces, IMO a
reasonable assembler would combine the pieces into a single section.
A quick glance at the SVR4 ELF doc does not say that the names of
sections in an ELF file must be unique. I can't guess whether this
is an oversight or intentional, but I always assumed that any given
section name would only appear once in an ELF file.
The thinking may be that if the linker is going to coalesce like-
named sections from multiple object files, it might as well do
the same for like-named sections in the same object file.
--
Michael Eager eager at eagercon.com
1960 Park Blvd., Palo Alto, CA 94306
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