Thanks again for all of the insight into all this. The reason we're looking into this is because we develop a tool that extracts dwarf info from an elf file called juicer <https://github.com/WindhoverLabs/juicer>, which dumps it into a SQLITE db for other tools. And we want to make sure we document all the various cases when it comes to different types of object files(shared, object file, executable/linked, etc) so that our users are aware of all of this.
In any case it looks I can apply relocations with the "-r" switch in gcc and I tried the following: gcc -r macro_test.o -o macro_test_relocatable After running dwarfdump on "macro_test.o" I get the following: Macro data from CU-DIE at .debug_info offset 0x0000000c: Macro version: 5 MacroInformationEntries count: 13, bytes length: 46 [ 0] 0x07 DW_MACRO_import offset 0x00000000 [ 1] 0x03 DW_MACRO_start_file line 0 file number 1 /usr/include/stdc-predef.h [ 2] 0x03 DW_MACRO_start_file line 31 file number 2 /home/lgomez/projects/openc3/cosmology/juicer/src/macro_test.h [ 3] 0x07 DW_MACRO_import offset 0x00000000 [ 4] 0x04 DW_MACRO_end_file [ 5] 0x05 DW_MACRO_define_strp line 1 str offset 0x00001de8 MAC1 2 [ 6] 0x05 DW_MACRO_define_strp line 2 str offset 0x000013bd MAC2 3 [ 7] 0x03 DW_MACRO_start_file line 3 file number 3 <src-index-high-no-source-file-name-available> [ 8] 0x07 DW_MACRO_import offset 0x00000000 [ 9] 0x04 DW_MACRO_end_file [ 10] 0x05 DW_MACRO_define_strp line 4 str offset 0x00002265 MAC3 4 [ 11] 0x04 DW_MACRO_end_file [ 12] 0x00 end-of-macros As you mentioned there is the "DW_MACRO_import", but it has an offset of "0x00000000". Which, if I'm interpreting the DWARF5 spec correctly, means "end of macros" for macro import units (and we still don't get the "MAC4", "MAC5" macros). And this makes sense in that this is what "dwarf_get_macro_import" returns when I step through code in juicer. And I believe that dwarfdump is using libdwarf too so that makes sense. So is this expected behavior as well? Essentially an object file has to be linked in order for all macros to show up under one debug_macro section? I apologize if this question sounds obvious/silly; I'm just trying to make sure I concretely document this for our tooling that depends on this... Again, Thanks so much for your time/explanations about this. It's much appreciated! On Thu, Sep 12, 2024 at 5:38 PM Jakub Jelinek <ja...@redhat.com> wrote: > On Thu, Sep 12, 2024 at 05:10:01PM -0500, Lorenzo Gomez wrote: > > Thanks so much for the detailed explanation. So clearly all the macros > are > > there as we can see from readelf. I ran it myself and can see all the > > macros as David pointed out. And just to make sure I understand, this is > > what I took away: > > > > 1. All the macros are in the file as we can see from readelf output. > > 2. As per the DWARF5 spec it states "As described in Section 3.1.1 on > page > > 60, the macro information for a given compilation unit is represented in > > the .debug_macro section of an object file." > > Meaning that there should be only *one*.debug_macro section, not > more > > than 1 as gcc is structuring it. > > Generally, in binaries/executables there is (at most) one .debug_* section > of > each kind with the different additions concatenated. > In object files, there can be many, that is something eventually linked > into > the output section. E.g. for comdat functions the producer could in ELF > emit separate .debug_info contributions in the comdat of the specific > function. > So, IMO nothing is violated, there is no bug, that is how .debug_macro > was meant to be used from the beginning (when what we implemented in GCC > as a DWARF 4 extension was then with small changes standardized in DWARF > 5). > If you are trying to look at debug info in object files rather than > binaries/shared libraries, you need to apply relocations, and the > DW_MACRO_import ops > have relocations to those corresponding .debug_macro contributions; > .debug_info compilation unit(s) also has DW_AT_macros attribute which > should have relocation pointing to the .debug_macro contribution where > the macros for that compilation unit start. And each DW_AT_import there > includes everything in the referenced contribution. > > Jakub > >
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