ELF program header table in MiniDebugInfo files

[Martin Milata]

Hello,
in the process of making ABRT aware of MiniDebugInfo[1] through the
libunwind library, I noticed that the MiniDebugInfo files in Fedora 19
(F18 too) have different ELF program header tables than the
corresponding binaries and separate debuginfo files:

  $ eu-readelf -l /usr/bin/cat
  Program Headers:
    Type           Offset   VirtAddr           PhysAddr           FileSiz  MemSiz   Flg Align
    PHDR           0x000040 0x0000000000400040 0x0000000000400040 0x0001f8 0x0001f8 R E 0x8
    INTERP         0x000238 0x0000000000400238 0x0000000000400238 0x00001c 0x00001c R   0x1
          [Requesting program interpreter: /lib64/ld-linux-x86-64.so.2]
    LOAD           0x000000 0x0000000000400000 0x0000000000400000 0x00b3e0 0x00b3e0 R E 0x200000
    LOAD           0x00bc30 0x000000000060bc30 0x000000000060bc30 0x0006f0 0x001078 RW  0x200000
    DYNAMIC        0x00bde8 0x000000000060bde8 0x000000000060bde8 0x0001d0 0x0001d0 RW  0x8
    NOTE           0x000254 0x0000000000400254 0x0000000000400254 0x000044 0x000044 R   0x4
    GNU_EH_FRAME   0x009a14 0x0000000000409a14 0x0000000000409a14 0x00030c 0x00030c R   0x4
    GNU_STACK      0x000000 0x0000000000000000 0x0000000000000000 0x000000 0x000000 RW  0x10
    GNU_RELRO      0x00bc30 0x000000000060bc30 0x000000000060bc30 0x0003d0 0x0003d0 R   0x1

  (snip)
  $ eu-readelf -l /usr/lib/debug/usr/bin/cat.debug
  Program Headers:
    Type           Offset   VirtAddr           PhysAddr           FileSiz  MemSiz   Flg Align
    PHDR           0x000040 0x0000000000400040 0x0000000000400040 0x0001f8 0x0001f8 R E 0x8
    INTERP         0x000238 0x0000000000400238 0x0000000000400238 0x00001c 0x00001c R   0x1
          [Requesting program interpreter: ]
    LOAD           0x000000 0x0000000000400000 0x0000000000400000 0x00ad14 0x00ad14 R E 0x200000
    LOAD           0x00bc30 0x000000000060bc30 0x000000000060bc30 0x0006f0 0x001078 RW  0x200000
    DYNAMIC        0x00bde8 0x000000000060bde8 0x000000000060bde8 0x0001d0 0x0001d0 RW  0x8
    NOTE           0x000254 0x0000000000400254 0x0000000000400254 0x000044 0x000044 R   0x4
    GNU_EH_FRAME   0x009a14 0x0000000000409a14 0x0000000000409a14 0x00030c 0x00030c R   0x4
    GNU_STACK      0x000000 0x0000000000000000 0x0000000000000000 0x000000 0x000000 RW  0x10
    GNU_RELRO      0x00bc30 0x000000000060bc30 0x000000000060bc30 0x0003d0 0x0003d0 R   0x1

  (snip)
  $ ./extract-elf-section.sh .gnu_debugdata /usr/bin/cat cat.mdi.xz # script attached
  $ xzdec cat.mdi.xz > cat.mdi
  $ readelf -l cat.mdi
  Program Headers:
    Type           Offset   VirtAddr           PhysAddr           FileSiz  MemSiz   Flg Align
    PHDR           0x000040 0x0000000000400060 0x0000000000400040 0x0001c0 0x0001c0 R E 0x8
    INTERP         0x000218 0x0000000000400238 0x0000000000400238 0x000000 0x00001c R   0x1
          [Requesting program interpreter: ]
    LOAD           0x000000 0x0000000000400020 0x0000000000400000 0x000298 0x00ad14 R E 0x20
    LOAD           0x0002b0 0x000000000060bc30 0x000000000060bc30 0x000000 0x001078 RW  0x20
    DYNAMIC        0x0002b0 0x000000000060bde8 0x000000000060bde8 0x000000 0x0001d0 RW  0x8
    NOTE           0x000274 0x0000000000400270 0x0000000000400254 0x000024 0x000024 R   0x4
    GNU_EH_FRAME   0x000298 0x0000000000409a14 0x0000000000409a14 0x000000 0x00030c R   0x4
    GNU_STACK      0x000000 0x0000000000000000 0x0000000000000000 0x000000 0x000000 RW  0x8
   (snip)

My problem is that the virtual address of the first LOAD segment changed.
Libunwind uses this value when resolving addresses to procedure names and
because the addresses in the symbol tables are the same in both debuginfo
files, the unexpected offset (of 0x20 here) causes it to return wrong result.

The addresses are changed by objcopy when removing sections and symbols
[2]. GDB doesn't seem to care. My question is, is the table supposed to
look like this and libunwind needs to be patched, or is it a bug? The
fact that the virtual address and physical address differ seems a bit
weird to me.

Cheers,
Martin Milata

[1] http://fedoraproject.org/wiki/Features/MiniDebugInfo
[2] http://sourceware.org/gdb/onlinedocs/gdb/MiniDebugInfo.html
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