delve/dwarf/line.Parse() only reads first directory table and file name table

[mpictor]

I guess this isn't an issue with ELF files generated by gc, but I'm trying to extract data from C++ libs. It would be nice if your dwarf package wasn't limited to golang 😄

If I use line.Parse() on the .debug_line section of one lib I have, it sees the files and dirs in the first pair of tables, but not the second pair.

On that file, readelf sees two dir tables and two file tables (see below).

I think line.Parse() shouldn't assume that all remaining data is instructions, as it does at line 45. I'm able to work around this by calling Parse() again on a slice starting at DebugLinePrologue.Length + 4. This appears to work correctly even on libraries with as many as 82 directory and file table pairs.

---

Output of $ readelf -Wwl /path/to/icu_data-l64d-4-0.so:

Raw dump of debug contents of section .debug_line:

  Offset:                      0x0
  Length:                      296
  DWARF Version:               2
  Prologue Length:             290
  Minimum Instruction Length:  1
  Initial value of 'is_stmt':  1
  Line Base:                   -5
  Line Range:                  14
  Opcode Base:                 13

 Opcodes:
  Opcode 1 has 0 args
  Opcode 2 has 1 args
  Opcode 3 has 1 args
  Opcode 4 has 1 args
  Opcode 5 has 1 args
  Opcode 6 has 0 args
  Opcode 7 has 0 args
  Opcode 8 has 0 args
  Opcode 9 has 1 args
  Opcode 10 has 0 args
  Opcode 11 has 0 args
  Opcode 12 has 1 args

 The Directory Table:
  /path/to/winhost/linux64/x86_64/x86_64-i3mingw32host-linux-gnu/sysroot/usr/include
  ../common/unicode
  /path/to/dists/icu/source/stubdata

 The File Name Table:
  Entry Dir     Time    Size    Name
  1     1       0       0       stdint.h
  2     2       0       0       udata.h
  3     3       0       0       stubdata.c

 Line Number Statements:

  Offset:                      0x12c
  Length:                      787
  DWARF Version:               2
  Prologue Length:             684
  Minimum Instruction Length:  1
  Initial value of 'is_stmt':  1
  Line Base:                   -5
  Line Range:                  14
  Opcode Base:                 13

 Opcodes:
  Opcode 1 has 0 args
  Opcode 2 has 1 args
  Opcode 3 has 1 args
  Opcode 4 has 1 args
  Opcode 5 has 1 args
  Opcode 6 has 0 args
  Opcode 7 has 0 args
  Opcode 8 has 0 args
  Opcode 9 has 1 args
  Opcode 10 has 0 args
  Opcode 11 has 0 args
  Opcode 12 has 1 args

 The Directory Table:
  /path/to/inc/system/somemoduleregistry
  gen/debug/l64/obj
  /path/to/winhost/linux64/x86_64/lib/gcc/x86_64-i3mingw32host-linux-gnu/4.8.1/include
  /path/to/winhost/linux64/x86_64/x86_64-i3mingw32host-linux-gnu/sysroot/usr/include/bits
  /path/to/winhost/linux64/x86_64/x86_64-i3mingw32host-linux-gnu/sysroot/usr/include

 The File Name Table:
  Entry Dir     Time    Size    Name
  1     1       0       0       registry.h
  2     2       0       0       tmp_manifest_datae58d12755ddb176ad98bdcc842e958ed.cpp
  3     3       0       0       stddef.h
  4     4       0       0       types.h
  5     5       0       0       libio.h
  6     1       0       0       common.h
  7     5       0       0       stdio.h

 Line Number Statements:
  Extended opcode 2: set Address to 0xdea
  Advance Line by 214 to 215
  Copy
  Special opcode 118: advance Address by 8 to 0xdf2 and Line by 1 to 216
  Special opcode 118: advance Address by 8 to 0xdfa and Line by 1 to 217
  Advance PC by 2 to 0xdfc
  Extended opcode 1: End of Sequence

  Set File Name to entry 2 in the File Name Table
<and so on...>

[derekparker]

I have thought about breaking the dwarf stuff out into a completely separate package, in case it would be useful for other projects.

Would you mind putting together a PR for this? Otherwise I'll keep this issue open and try to get to it as soon as I can.

[mpictor]

I wish I had the time, but I don't. Sorry!