vendor/gimli/fixtures/self/README.md

   1 # What are these files?
   2
   3 These files are the DWARF data generated for (an early version of) this
   4 library. Each file corresponds is a section from the built library's object
   5 file. By splitting the sections out to their own files, we don't need to worry
   6 about cross platform and cross object file format issues when running examples.
   7
   8 # Updating and adding new sections
   9
  10 ## macOS
  11
  12 Use `otool` to list the sections of a binary:
  13
  14 ```
  15 $ otool -l path/to/binary
  16 ```
  17
  18 You should see output similar to this:
  19
  20 ```
  21 Load command 0
  22       cmd LC_SEGMENT_64
  23   cmdsize 72
  24   segname __PAGEZERO
  25    vmaddr 0x0000000000000000
  26    vmsize 0x0000000100000000
  27   fileoff 0
  28  filesize 0
  29   maxprot 0x00000000
  30  initprot 0x00000000
  31    nsects 0
  32     flags 0x0
  33 Load command 1
  34       cmd LC_SEGMENT_64
  35   cmdsize 712
  36   segname __TEXT
  37    vmaddr 0x0000000100000000
  38    vmsize 0x00000000001b7000
  39   fileoff 0
  40  filesize 1798144
  41   maxprot 0x00000007
  42  initprot 0x00000005
  43    nsects 8
  44     flags 0x0
  45 Section
  46   sectname __text
  47    segname __TEXT
  48       addr 0x0000000100000a50
  49       size 0x0000000000170716
  50     offset 2640
  51      align 2^4 (16)
  52     reloff 0
  53     nreloc 0
  54      flags 0x80000400
  55  reserved1 0
  56  reserved2 0
  57 ```
  58
  59 Etc.
  60
  61 Find the `Section` entry of the section you'd like to isolate. For example, if
  62 you're looking for `eh_frame`, find an entry like this:
  63
  64 ```
  65 Section
  66   sectname __eh_frame
  67    segname __TEXT
  68       addr 0x0000000100192f38
  69       size 0x00000000000240c8
  70     offset 1650488
  71      align 2^3 (8)
  72     reloff 0
  73     nreloc 0
  74      flags 0x00000000
  75  reserved1 0
  76  reserved2 0
  77 ```
  78
  79 Then use `dd` to copy `size` bytes starting from `offset`:
  80
  81 ```
  82 $ dd bs=1 skip=1650488 count=$(printf "%d" 0x00000000000240c8) if=path/to/binary of=fixtures/self/eh_frame
  83 ```
  84
  85 Finally, use `otool` and `hexdump` to verify that the isolated section has the
  86 same data as the section within the binary:
  87
  88 ```
  89 $ otool -s __TEXT __eh_frame path/to/binary | head
  90 path/to/binary:
  91 Contents of (__TEXT,__eh_frame) section
  92 0000000100192f38        14 00 00 00 00 00 00 00 01 7a 52 00 01 78 10 01
  93 0000000100192f48        10 0c 07 08 90 01 00 00 24 00 00 00 1c 00 00 00
  94 0000000100192f58        f8 da e6 ff ff ff ff ff 66 00 00 00 00 00 00 00
  95 0000000100192f68        00 41 0e 10 86 02 43 0d 06 00 00 00 00 00 00 00
  96 0000000100192f78        1c 00 00 00 00 00 00 00 01 7a 50 4c 52 00 01 78
  97 0000000100192f88        10 07 9b 9d 40 02 00 10 10 0c 07 08 90 01 00 00
  98 0000000100192f98        2c 00 00 00 24 00 00 00 20 db e6 ff ff ff ff ff
  99 0000000100192fa8        8d 00 00 00 00 00 00 00 08 37 e7 fd ff ff ff ff
 100
 101 $ otool -s __TEXT __eh_frame path/to/binary | tail
 102 00000001001b6f68        9a 0a 00 00 00 00 00 00 00 41 0e 10 86 02 43 0d
 103 00000001001b6f78        06 50 83 07 8c 06 8d 05 8e 04 8f 03 00 00 00 00
 104 00000001001b6f88        24 00 00 00 7c 0e 00 00 30 a0 fb ff ff ff ff ff
 105 00000001001b6f98        15 00 00 00 00 00 00 00 00 41 0e 10 86 02 43 0d
 106 00000001001b6fa8        06 00 00 00 00 00 00 00 24 00 00 00 a4 0e 00 00
 107 00000001001b6fb8        28 a0 fb ff ff ff ff ff 1c 00 00 00 00 00 00 00
 108 00000001001b6fc8        00 41 0e 10 86 02 43 0d 06 00 00 00 00 00 00 00
 109 00000001001b6fd8        24 00 00 00 cc 0e 00 00 20 a0 fb ff ff ff ff ff
 110 00000001001b6fe8        66 01 00 00 00 00 00 00 00 41 0e 10 86 02 43 0d
 111 00000001001b6ff8        06 00 00 00 00 00 00 00
 112 ```
 113
 114 This should be the same, ignoring the leading offsets:
 115
 116 ```
 117 $ hexdump fixtures/self/eh_frame | head
 118 0000000 14 00 00 00 00 00 00 00 01 7a 52 00 01 78 10 01
 119 0000010 10 0c 07 08 90 01 00 00 24 00 00 00 1c 00 00 00
 120 0000020 f8 da e6 ff ff ff ff ff 66 00 00 00 00 00 00 00
 121 0000030 00 41 0e 10 86 02 43 0d 06 00 00 00 00 00 00 00
 122 0000040 1c 00 00 00 00 00 00 00 01 7a 50 4c 52 00 01 78
 123 0000050 10 07 9b 9d 40 02 00 10 10 0c 07 08 90 01 00 00
 124 0000060 2c 00 00 00 24 00 00 00 20 db e6 ff ff ff ff ff
 125 0000070 8d 00 00 00 00 00 00 00 08 37 e7 fd ff ff ff ff
 126 0000080 ff 41 0e 10 86 02 43 0d 06 00 00 00 00 00 00 00
 127 0000090 24 00 00 00 94 00 00 00 80 db e6 ff ff ff ff ff
 128
 129 $ hexdump fixtures/self/eh_frame | tail
 130 0024040 06 50 83 07 8c 06 8d 05 8e 04 8f 03 00 00 00 00
 131 0024050 24 00 00 00 7c 0e 00 00 30 a0 fb ff ff ff ff ff
 132 0024060 15 00 00 00 00 00 00 00 00 41 0e 10 86 02 43 0d
 133 0024070 06 00 00 00 00 00 00 00 24 00 00 00 a4 0e 00 00
 134 0024080 28 a0 fb ff ff ff ff ff 1c 00 00 00 00 00 00 00
 135 0024090 00 41 0e 10 86 02 43 0d 06 00 00 00 00 00 00 00
 136 00240a0 24 00 00 00 cc 0e 00 00 20 a0 fb ff ff ff ff ff
 137 00240b0 66 01 00 00 00 00 00 00 00 41 0e 10 86 02 43 0d
 138 00240c0 06 00 00 00 00 00 00 00
 139 ```
 140
 141 ## Linux
 142
 143 Something like this:
 144
 145 ```
 146 objcopy --dump-section .eh_frame=fixtures/self/eh_frame path/to/binary
 147 ```