[Bug tapsets/30407] Tapset function print_ubacktrace_fileline() no longer works on kernel 6.2/6.1

["mcermak at redhat dot com" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=30407

Martin Cermak <mcermak at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |mcermak at redhat dot com

--- Comment #2 from Martin Cermak <mcermak at redhat dot com> ---
This can be replicated with rhel8 (works) versusus rhel9 (doesn't work).  But I
don't think it's related to kernel:  After copying my test binary from rhel8
over to rhel9 (and making sure it's md5-identical, things started to work even
on rhel9!

The following comes from my rhel8 binary where things work fine:

> 8 x86_64 # eu-readelf --debug-dump=info a.out 
> 
> DWARF section [26] '.debug_info' at offset 0x2e70:
>  [Offset]
>  Compilation unit at offset 0:
>  Version: 4, Abbreviation section offset: 0, Address size: 8, Offset size: 4
>  [     b]  compile_unit         abbrev: 1
>            producer             (strp) "GNU C17 8.5.0 20210514 (Red Hat 8.5.0-19) -mtune=generic -march=x86-64 -g"
>            language             (data1) C99 (12)
>            name                 (strp) "test.c"
>            comp_dir             (strp) "/root/build"
>            low_pc               (addr) 0x0000000000400536 <main>
>            high_pc              (data8) 11 (0x0000000000400541)
>            stmt_list            (sec_offset) 0
>  [    2d]    subprogram           abbrev: 2
>              external             (flag_present) yes
>              name                 (strp) "main"
>              decl_file            (data1) test.c (1)
>              decl_line            (data1) 1
>              decl_column          (data1) 5
>              prototyped           (flag_present) yes
>              type                 (ref4) [    4b]
>              low_pc               (addr) 0x0000000000400536 <main>
>              high_pc              (data8) 11 (0x0000000000400541)
>              frame_base           (exprloc) 
>               [ 0] call_frame_cfa
>              GNU_all_call_sites   (flag_present) yes
>  [    4b]    base_type            abbrev: 3
>              byte_size            (data1) 4
>              encoding             (data1) signed (5)
>              name                 (string) "int"
> 8 x86_64 #

Now here's what my rhel9 binary shows:

> 9 x86_64 # eu-readelf --debug-dump=info a.out 
> 
> DWARF section [27] '.debug_info' at offset 0x47a0:
>  [Offset]
>  Compilation unit at offset 0:
>  Version: 5, Abbreviation section offset: 0, Address size: 8, Offset size: 4
>  Unit type: compile (1)
>  [     c]  compile_unit         abbrev: 1
>            producer             (strp) "GNU C17 11.3.1 20221121 (Red Hat 11.3.1-4) -mtune=generic -march=x86-64-v2 -g"
>            language             (data1) C11 (29)
>            name                 (line_strp) "test.c"
>            comp_dir             (line_strp) "/root/build"
>            low_pc               (addr) 0x0000000000401106 <main>
>            high_pc              (data8) 11 (0x0000000000401111)
>            stmt_list            (sec_offset) 0
>  [    2e]    subprogram           abbrev: 2
>              external             (flag_present) yes
>              name                 (strp) "main"
>              decl_file            (data1) test.c (1)
>              decl_line            (data1) 1
>              decl_column          (data1) 5
>              prototyped           (flag_present) yes
>              type                 (ref4) [    4c]
>              low_pc               (addr) 0x0000000000401106 <main>
>              high_pc              (data8) 11 (0x0000000000401111)
>              frame_base           (exprloc) 
>               [ 0] call_frame_cfa
>              call_all_calls       (flag_present) yes
>  [    4c]    base_type            abbrev: 3
>              byte_size            (data1) 4
>              encoding             (data1) signed (5)
>              name                 (string) "int"
> 9 x86_64 # 

I've verified that -march, doesn't cause the difference.  But enforcing DWARF4
on rhel9 with `gcc -gdwarf-4` makes things work again on rhel9!  So I think
it's the DWARF version that makes the difference :)


The print_ubacktrace_fileline() call propagates down to
_stp_linenumber_lookup(address, task, &filename, ...) which already returns the
NULL filename.  Stepping in, this calls _stp_linenumber_lookup(), which returns
struct _stp_module with a NULL debug_line member.  Looking farther...

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