title: Explaining readelf -S output
body: <p>I'm trying to load an elf file into a MIPS simulator I made.  The problem I'm having is that I don't quite understand the meaning behind the elf section header offset.  When I do a segment dump, segments 25 - 31 and 33 - 35 "start" at 0x00000000 but the header states that the segment starts at an offset of some value (ex. 010190).  Also at the beginning of the -S section readelf states that the headers start in memory at 0x107b4.  But as can be seen in -S, the earliest memory allocation (because segment 0 is empty)  is actually in segment 26 at offset 010210.  Can someone explain what's going on here?  I want to statically allocate all of this file into a memory array.  Is there some assumption about offsets that's preventing me from doing this?  And why does readelf say  0x107b4 is the header starting point?</p>
  
  <p>Also, should I be running <code>.init</code> before I place the PC at the "entry point" specified by readelf?</p>
  
  <p>EDIT: Okay, so, I did a hex dump of the executable file and I now realize that the offset is referring to the location in the actual elf file (contains elements at "addresses" 0 - 11d48.) So my question now is... how do I resolve the fact that many of the memory addresses reference address 0x00000000? They have different offsets of course but now that I know that is file specific, it means that several section alias. Do I actually use the offsets in memory addressing?</p>
  
  <p>Segment 25:</p>
  
  <pre><code>  0x00000000 00474343 3a202847 4e552920 332e342e .GCC: (GNU) 3.4.
    0x00000010 35000047 43433a20 ...
  </code></pre>
  
  <p><code>Readelf -S</code> output:</p>
  
  <pre><code>  There are 36 section headers, starting at offset 0x107b4:
  </code></pre>
  
  <p>Section Headers:</p>
  
  <pre><code>  [Nr] Name              Type            Addr     Off    Size   ES Flg Lk Inf Al
    [ 0]                   NULL            00000000 000000 000000 00      0   0  0
    [ 1] .interp           PROGBITS        00400134 000134 00000d 00   A  0   0  1
    [ 2] .note.ABI-tag     NOTE            00400144 000144 000020 00   A  0   0  4
    [ 3] .reginfo          MIPS_REGINFO    00400164 000164 000018 18   A  0   0  4
    [ 4] .dynamic          DYNAMIC         0040017c 00017c 000108 08   A  7   0  4
    [ 5] .hash             HASH            00400284 000284 0000bc 04   A  6   0  4
    [ 6] .dynsym           DYNSYM          00400340 000340 0001c0 10   A  7   1  4
    [ 7] .dynstr           STRTAB          00400500 000500 00023c 00   A  0   0  1
    [ 8] .gnu.version      VERSYM          0040073c 00073c 000038 02   A  6   0  2
    [ 9] .gnu.version_r    VERNEED         00400774 000774 000060 00   A  7   2  4
    [10] .init             PROGBITS        004007e4 0007e4 0000a8 00  AX  0   0  4
    [11] .text             PROGBITS        00400890 000890 000810 00  AX  0   0 16
    [12] .MIPS.stubs       PROGBITS        004010a0 0010a0 000090 00  AX  0   0  4
    [13] .fini             PROGBITS        00401130 001130 000058 00  AX  0   0  4
    [14] .rodata           PROGBITS        00401190 001190 000020 00   A  0   0 16
    [15] .eh_frame_hdr     PROGBITS        004011b0 0011b0 000034 00   A  0   0  4
    [16] .data             PROGBITS        10000000 010000 000030 00  WA  0   0 16
    [17] .rld_map          PROGBITS        10000030 010030 000004 00  WA  0   0  4
    [18] .eh_frame         PROGBITS        10000034 010034 0000bc 00  WA  0   0  4
    [19] .ctors            PROGBITS        100000f0 0100f0 00000c 00  WA  0   0  4
    [20] .dtors            PROGBITS        100000fc 0100fc 000008 00  WA  0   0  4
    [21] .jcr              PROGBITS        10000104 010104 000004 00  WA  0   0  4
    [22] .got              PROGBITS        10000110 010110 00007c 04 WAp  0   0 16
    [23] .sbss             NOBITS          1000018c 010190 000000 00 WAp  0   0  1
    [24] .bss              NOBITS          10000190 010190 000020 00  WA  0   0 16
    [25] .comment          PROGBITS        00000000 010190 00007e 00      0   0  1
    [26] .debug_aranges    MIPS_DWARF      00000000 010210 000058 00      0   0  8
    [27] .debug_info       MIPS_DWARF      00000000 010268 000146 00      0   0  1
    [28] .debug_abbrev     MIPS_DWARF      00000000 0103ae 000020 00      0   0  1
    [29] .debug_line       MIPS_DWARF      00000000 0103ce 0001a6 00      0   0  1
    [30] .pdr              PROGBITS        00000000 010574 000100 00      0   0  4
    [31] .mdebug.abi32     PROGBITS        00000000 010674 000000 00      0   0  1
    [32] .rel.dyn          REL             004007d4 0007d4 000010 08   A  6   0  4
    [33] .shstrtab         STRTAB          00000000 010674 00013f 00      0   0  1
    [34] .symtab           SYMTAB          00000000 010d54 000920 10     35 107  4
    [35] .strtab           STRTAB          00000000 011674 0006d4 00      0   0  1
  </code></pre>