DWARF support

[bjorn3]

• Unmangled symbols names (Various small debuginfo improvements #1470)
• Arguments and locals
• Statics (Add debuginfo for statics #1472)
• Types
• Line info (Implement line debuginfo #291)
• Inlining information (long term)
• Backtrace information (Implement .eh_frame writing #982)
• Unwinding information (long term)

Edit: add unwinding information
Edit2: state which things are for the long term
Edit3: gimli-rs/gimli#340 has been merged
Edit4: m4b/faerie#51 has been merged and CraneStation/cranelift#426 is not necessary anymore I believe.

[philipc]

Does this cover eh_frame too?

[bjorn3]

Added

[bjorn3]

From m4b/faerie#51 (comment) by @philipc:

https://github.com/philipc/rustc_codegen_cranelift/tree/debuginfo
https://github.com/philipc/cranelift/tree/debug

Both still WIP. The rustc support will be better once it's using more of rustc_codegen_ssa (eg it has set_debug_loc() calls in all the right places). I'm currently working on .debug_line support in gimli.

I don't see the .debug_info contents. :(

(please note that I had to rebase both branches to get it working with the latest nightly)

$ llvm-dwarfdump-3.8 target/out/mini_core_hello_world
target/out/mini_core_hello_world:       file format ELF64-x86-64

.debug_abbrev contents:
Abbrev table for offset: 0x00000000
[1] DW_TAG_compile_unit DW_CHILDREN_yes
        DW_AT_producer  DW_FORM_strp
        DW_AT_language  DW_FORM_udata
        DW_AT_name      DW_FORM_strp
        DW_AT_comp_dir  DW_FORM_strp

[2] DW_TAG_subprogram   DW_CHILDREN_no
        DW_AT_linkage_name      DW_FORM_strp
        DW_AT_decl_file DW_FORM_strp
        DW_AT_decl_line DW_FORM_udata
        DW_AT_decl_column       DW_FORM_udata

Abbrev table for offset: 0x0000001b
[1] DW_TAG_compile_unit DW_CHILDREN_yes
        DW_AT_producer  DW_FORM_strp
        DW_AT_language  DW_FORM_udata
        DW_AT_name      DW_FORM_strp
        DW_AT_comp_dir  DW_FORM_strp

[2] DW_TAG_subprogram   DW_CHILDREN_no
        DW_AT_linkage_name      DW_FORM_strp
        DW_AT_decl_file DW_FORM_strp
        DW_AT_decl_line DW_FORM_udata
        DW_AT_decl_column       DW_FORM_udata


.debug_abbrev.dwo contents:
< EMPTY >

.debug_info contents:

.debug_loc contents:

.debug_loc.dwo contents:

.debug_frame contents:


.debug_macinfo contents:

.debug_aranges contents:

.debug_line contents:

.debug_cu_index contents:

.debug_tu_index contents:

.debug_line.dwo contents:

.debug_str contents:
0x00000000: "example/mini_core_hello_world.rs"
0x00000021: "/home/bjorn/Documenten/rustc_codegen_cranelift"
0x00000050: "cranelift (rustc version unknown version)"
0x0000007a: "_ZN21mini_core_hello_world4main17he1655d58f9d91204E"
0x000000ae: "_ZN68_$LT$mini_core_hello_world..NoisyDrop$u20$as$u20$mini_core..Drop$GT$4drop17h6f94045255c03089E"
0x00000111: "_ZN63_$LT$$LP$$RP$$u20$as$u20$mini_core_hello_world..Termination$GT$6report17hdb0778df210e78ccE"
0x00000171: "_ZN9mini_core13drop_in_place17hce2f1c802ab2620fE"
0x000001a2: "/home/bjorn/Documenten/rustc_codegen_cranelift/example/mini_core.rs"
0x000001e6: "_ZN21mini_core_hello_world5start17h1e715bf6fab28115E"
0x0000021b: "_ZN9mini_core13drop_in_place17hd9450b03d573a12fE"
0x0000024c: "_ZN73_$LT$mini_core_hello_world..NoisyDropInner$u20$as$u20$mini_core..Drop$GT$4drop17h47d84ca54e8a334aE"
0x000002b4: "_ZN9mini_core13drop_in_place17h916a3813cccd8138E"
0x000002e5: "_ZN76_$LT$$RF$$u27$static$u20$str$u20$as$u20$mini_core_hello_world..SomeTrait$GT$11object_safe17ha78f10b266d14c40E"
0x00000358: "_ZN9mini_core13drop_in_place17h0dfa83ab1d2ac08dE"
0x00000389: "example/mini_core.rs"
0x0000039e: "/home/bjorn/Documenten/rustc_codegen_cranelift"
0x000003cd: "cranelift (rustc version unknown version)"
0x000003f7: "_ZN9mini_core8allocate17h122bb7e874c2cf63E"
0x00000422: "_ZN37_$LT$u8$u20$as$u20$mini_core..Add$GT$3add17h2ed4592d072eae4dE"
0x00000465: "_ZN68_$LT$$RF$$u27$a$u20$bool$u20$as$u20$mini_core..BitOr$LT$bool$GT$$GT$5bitor17hbdb95c272ef985e2E"
0x000004c9: "_ZN40_$LT$usize$u20$as$u20$mini_core..Sub$GT$3sub17h5e441af28e85913cE"
0x0000050f: "_ZN43_$LT$u8$u20$as$u20$mini_core..PartialEq$GT$2eq17h19e3d34341b7ef63E"
0x00000557: "_ZN37_$LT$u8$u20$as$u20$mini_core..Mul$GT$3mul17h1b0786eb335e6b00E"
0x0000059a: "_ZN41_$LT$bool$u20$as$u20$mini_core..BitOr$GT$5bitor17h7c5a454fe7ec849bE"
0x000005e3: "_ZN45_$LT$char$u20$as$u20$mini_core..PartialEq$GT$2ne17h3bbde2eaedbb9611E"
0x0000062d: "_ZN39_$LT$bool$u20$as$u20$mini_core..Not$GT$3not17hd55c09678b9ff6b0E"
0x00000672: "_ZN40_$LT$isize$u20$as$u20$mini_core..Neg$GT$3neg17h61958dbcef5ebc0fE"
0x000006b8: "_ZN45_$LT$char$u20$as$u20$mini_core..PartialEq$GT$2eq17hdae5677cbecc8595E"
0x00000702: "_ZN43_$LT$u8$u20$as$u20$mini_core..PartialEq$GT$2ne17hc2dba50b5506e1e4E"
0x0000074a: "rust_eh_personality"
0x0000075e: "_ZN9mini_core5panic17h1b8c87c5633941c5E"

.debug_ranges contents:

.debug_pubnames contents:

.debug_pubtypes contents:

.debug_gnu_pubnames contents:

.debug_gnu_pubtypes contents:

.apple_names contents:

.apple_types contents:

.apple_namespaces contents:

.apple_objc contents:

$ readelf --sections target/out/mini_core_hello_world
There are 31 section headers, starting at offset 0x51a8:

Section Headers:
  [Nr] Name              Type             Address           Offset
       Size              EntSize          Flags  Link  Info  Align
  [ 0]                   NULL             0000000000000000  00000000
       0000000000000000  0000000000000000           0     0     0
  [ 1] .interp           PROGBITS         0000000000000238  00000238
       000000000000001c  0000000000000000   A       0     0     1
  [ 2] .note.ABI-tag     NOTE             0000000000000254  00000254
       0000000000000020  0000000000000000   A       0     0     4
  [ 3] .note.gnu.build-i NOTE             0000000000000274  00000274
       0000000000000024  0000000000000000   A       0     0     4
  [ 4] .gnu.hash         GNU_HASH         0000000000000298  00000298
       000000000000001c  0000000000000000   A       5     0     8
  [ 5] .dynsym           DYNSYM           00000000000002b8  000002b8
       00000000000000c0  0000000000000018   A       6     1     8
  [ 6] .dynstr           STRTAB           0000000000000378  00000378
       0000000000000096  0000000000000000   A       0     0     1
  [ 7] .gnu.version      VERSYM           000000000000040e  0000040e
       0000000000000010  0000000000000002   A       5     0     2
  [ 8] .gnu.version_r    VERNEED          0000000000000420  00000420
       0000000000000020  0000000000000000   A       6     1     8
  [ 9] .rela.dyn         RELA             0000000000000440  00000440
       00000000000003a8  0000000000000018   A       5     0     8
  [10] .init             PROGBITS         00000000000007e8  000007e8
       0000000000000017  0000000000000000  AX       0     0     4
  [11] .plt              PROGBITS         0000000000000800  00000800
       0000000000000010  0000000000000010  AX       0     0     16
  [12] .plt.got          PROGBITS         0000000000000810  00000810
       0000000000000010  0000000000000000  AX       0     0     8
  [13] .text             PROGBITS         0000000000000820  00000820
       00000000000014dd  0000000000000000  AX       0     0     16
  [14] .fini             PROGBITS         0000000000001d00  00001d00
       0000000000000009  0000000000000000  AX       0     0     4
  [15] .eh_frame_hdr     PROGBITS         0000000000001d0c  00001d0c
       0000000000000034  0000000000000000   A       0     0     4
  [16] .eh_frame         PROGBITS         0000000000001d40  00001d40
       00000000000000ec  0000000000000000   A       0     0     8
  [17] .init_array       INIT_ARRAY       0000000000202dd8  00002dd8
       0000000000000008  0000000000000008  WA       0     0     8
  [18] .fini_array       FINI_ARRAY       0000000000202de0  00002de0
       0000000000000008  0000000000000008  WA       0     0     8
  [19] .jcr              PROGBITS         0000000000202de8  00002de8
       0000000000000008  0000000000000000  WA       0     0     8
  [20] .dynamic          DYNAMIC          0000000000202df0  00002df0
       00000000000001c0  0000000000000010  WA       6     0     8
  [21] .got              PROGBITS         0000000000202fb0  00002fb0
       0000000000000050  0000000000000008  WA       0     0     8
  [22] .data             PROGBITS         0000000000203000  00003000
       0000000000000530  0000000000000000  WA       0     0     8
  [23] .bss              NOBITS           0000000000203530  00003530
       0000000000000008  0000000000000000  WA       0     0     1
  [24] .comment          PROGBITS         0000000000000000  00003530
       000000000000002d  0000000000000001  MS       0     0     1
  [25] .debug_info       PROGBITS         0000000000000000  0000355d
       000000000000014c  0000000000000000           0     0     1
  [26] .debug_abbrev     PROGBITS         0000000000000000  000036a9
       0000000000000036  0000000000000000           0     0     1
  [27] .debug_str        PROGBITS         0000000000000000  000036df
       0000000000000786  0000000000000000           0     0     1
  [28] .symtab           SYMTAB           0000000000000000  00003e68
       0000000000000bb8  0000000000000018          29    92     8
  [29] .strtab           STRTAB           0000000000000000  00004a20
       0000000000000668  0000000000000000           0     0     1
  [30] .shstrtab         STRTAB           0000000000000000  00005088
       000000000000011b  0000000000000000           0     0     1
Key to Flags:
  W (write), A (alloc), X (execute), M (merge), S (strings), I (info),
  L (link order), O (extra OS processing required), G (group), T (TLS),
  C (compressed), x (unknown), o (OS specific), E (exclude),
  l (large), p (processor specific)

$ readelf --hex-dump=.debug_info target/out/mini_core_hello_world

Hex dump of section '.debug_info':
  0x00000000 89000000 05000108 00000000 01500000 .............P..
  0x00000010 001c0000 00002100 0000027a 00000000 ......!....z....
  0x00000020 00000076 0002ae00 00000000 00003e04 ...v..........>.
  0x00000030 02110100 00000000 00220402 71010000 ........."..q...
  0x00000040 a2010000 ee010002 e6010000 00000000 ................
  0x00000050 5400021b 020000a2 010000ee 0100024c T..............L
  0x00000060 02000000 00000046 0402b402 0000a201 .......F........
  0x00000070 0000ee01 0002e502 00000000 00002f04 ............../.
  0x00000080 02580300 00a20100 00ee0100 00bb0000 .X..............
  0x00000090 00050001 081b0000 0001cd03 00001c89 ................
  0x000000a0 0300009e 03000002 f7030000 89030000 ................
  0x000000b0 fc010002 22040000 89030000 6c040265 ....".......l..e
  0x000000c0 04000089 03000093 010402c9 04000089 ................
  0x000000d0 0300007b 04020f05 00008903 00009f01 ...{............
  0x000000e0 04025705 00008903 00005d04 029a0500 ..W.......].....
  0x000000f0 00890300 008b0104 02e30500 00890300 ................
  0x00000100 00ab0104 022d0600 00890300 004d0402 .....-.......M..
  0x00000110 72060000 89030000 c3010402 b8060000 r...............
  0x00000120 89030000 a8010402 02070000 89030000 ................
  0x00000130 a2010402 4a070000 89030000 e8010002 ....J...........
  0x00000140 5e070000 89030000 e1010000          ^...........

Posting here, because I think this is a more appropriate place to continue this conversation.

[philipc]

I'll look into it later today, but maybe you need to change the DWARF version to 4. I've been using gimli's dwarfdump, I'll try llvm-dwarfdump later.

[bjorn3]

Thanks. Using version 4 fixes it.

[bjorn3]

I rebased @philipc's debuginfo branch and extended it a bit.

It is currently blocked on bytecodealliance/cranelift#651 (merged) and m4b/faerie#59 (merged)

[bjorn3]

_argc=<optimized out> here confuses me, because I provided DW_AT_location.

~/Documents/rustc_codegen_cranelift(philipc_debuginfo_updated*) » gdb target/out/mini_core_hello_world
[...]
(gdb) break main
Breakpoint 1 at 0x1db0
(gdb) run
Starting program: /home/bjorn/Documents/rustc_codegen_cranelift/target/out/mini_core_hello_world

Breakpoint 1, 0x0000000008001db0 in main ()
(gdb) si
0x0000000008001db2 in main ()
[...]
0x0000000008001dc5 in main ()
(gdb) si
0x0000000008000a00 in mini_core_hello_world::start::h1e715bf6fab28115 (main=..., _argc=<optimized out>, _argv=...)

[philipc]

Looks like gdb ignores DW_TAG_formal_parameter if a DW_TAG_variable shadows it, since deleting the DW_TAG_variable gives:

Breakpoint 1, 0x0000555555555b70 in mini_core_hello_world::start::h1e715bf6fab28115 (main=..., _argc=1, _argv=...)

This duplication of arguments as variables is unnecessary and should be avoided (see rust-lang/rust#45380).

[bjorn3]

Thanks. I renamed the DW_TAG_formal_parameter for now.

[bjorn3]

Note to self:

• DW_AT_variable_parameter for DW_TAG_formal_parameter
• .debug_loc for changing variable locations
• http://dwarfstd.org/doc/DWARF4.pdf
• DW_AT_stmt_list on DW_TAG_compile_unit is needed for line info.
• According https://llvm.org/devmtg/2014-10/Slides/Christopher-DebugInfoTutorial.pdf omitting is_stmt causes gdb to do strange things.
• https://events.static.linuxfound.org/images/stories/pdf/lfcs2012_eager.pdf
• http://dwarfstd.org/doc/Debugging%20using%20DWARF-2012.pdf

[bjorn3]

@philipc could you advise me some other sources about DWARF information than the spec?

[philipc]

Most of my information comes from:

• DWARF spec
• inspecting binaries using dwarfdump/llvm-dwarfdump/readelf
• reading LLVM/gdb source code

If you have a specific question I can try to answer.