[Dwarf-Discuss] armcc DWARF
Wed May 23 09:33:14 GMT 2018
- Why is .debug_abbrev in a group by itself?
So that it can be placed into a COMDAT group and the linker can ensure that only one copy of the .debug_abbrev sections appears in the final image.
armcc generates a fixed table of entries into the .debug_abbrev section, so this allows the linker to ensure only one copy ends up in the final image. All .debug_info sections in a .o file reference this one .debug_abbrev section.
This is different to many other compilers which generate a .debug_abbrev section which only contains the entries required by a single .debug_info section; thus each .debug_abbrev section is different. The resulting table in the final image, which concatenates all the .debug_abbrev sections together, may therefore be larger than having a single table of fixed entries.
- There are two .debug_info not in any group
Armcc partitions up the debugging information in order to allow debugging information to be removed from the final image if the associated code/data is removed.
The debugging information that should always be retained (usually type information) will be placed into sections not in a group.
The debugging information that is associated with code/data that could be discarded by the linker will be placed into the same group section; so if the code/data is discarded so is the associated debugging information. The .debug_info entries in a group section will often reference type entries in the .debug_info section which is always retained.
The often happens for C++ code, or if you are generating each function into its own section to allow the linker to discard unused functions.
- Which .debug_line (sec 7 or 8)would be referred to from section 6 debug_line? How would one know?
The magic of relocation entries. The DW_AT_stmt_list entry in section 6 should have an associated relocation entry whose symbol is associated with the section to which it refers.
From: Dwarf-Discuss <firstname.lastname@example.org> On Behalf Of David Anderson via Dwarf-Discuss
Sent: 22 May 2018 22:33
To: dwarf-discuss at lists.dwarfstd.org
Subject: [Dwarf-Discuss] armcc DWARF
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)
Here is dwarfdump/libdwarf/s reading of the sections and section-group sections.
Section Groups data
Number of Elf-like sections: 35
Number of groups : 5
Group to print : 3
Count of map entries : 15
[index] group section
[ 0] 1 4 .debug_frame
[ 1] 1 5 .debug_info
[ 2] 1 6 .debug_info
[ 3] 1 7 .debug_line
[ 4] 1 8 .debug_line
[ 5] 1 9 .debug_loc
[ 6] 1 10 .debug_macinfo
[ 7] 1 11 .debug_pubnames
[ 8] 3 13 .debug_info
[ 9] 3 14 .debug_line
[ 10] 4 16 .debug_info
[ 11] 5 18 .debug_info
[ 12] 5 19 .debug_line
[ 13] 5 20 .debug_macinfo
[ 14] 6 22 .debug_abbrev
There are two .debug_info not in any group (called group 1 by libdwarf).
There is only one .debug_abbrev and it is in group six.
How is one to make sense of this? Which .debug_line (sec 7 or 8)would be referred to from section 6 debug_line? How would one know?
Why is .debug_abbrev in a group by itself?
I would appreciate any information on how the sections tie together...
how is a reader supposed to know what goes with what?
Thanks for any hints.
Duct tape is like the force. It has a light side, a dark side, and it holds the universe together.... -- Carl Zwanzig
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