mingw/info/gdb/Machine-Code.html

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  12 Node:<a name="Machine%20Code">Machine Code</a>,
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  17
  18 <h3 class="section">Source and machine code</h3>
  19
  20    <p>You can use the command <code>info line</code> to map source lines to program
  21 addresses (and vice versa), and the command <code>disassemble</code> to display
  22 a range of addresses as machine instructions.  When run under <small>GNU</small> Emacs
  23 mode, the <code>info line</code> command causes the arrow to point to the
  24 line specified.  Also, <code>info line</code> prints addresses in symbolic form as
  25 well as hex.
  26
  27      <dl>
  28 <dt><code>info line </code><var>linespec</var><code></code>
  29      <dd>Print the starting and ending addresses of the compiled code for
  30 source line <var>linespec</var>.  You can specify source lines in any of
  31 the ways understood by the <code>list</code> command (see <a href="List.html#List">Printing source lines</a>).
  32 </dl>
  33
  34    <p>For example, we can use <code>info line</code> to discover the location of
  35 the object code for the first line of function
  36 <code>m4_changequote</code>:
  37
  38 <pre class="smallexample">     (gdb) info line m4_changequote
  39      Line 895 of "builtin.c" starts at pc 0x634c and ends at 0x6350.
  40      </pre>
  41
  42 <p>We can also inquire (using <code>*</code><var>addr</var><code></code> as the form for
  43 <var>linespec</var>) what source line covers a particular address:
  44 <pre class="smallexample">     (gdb) info line *0x63ff
  45      Line 926 of "builtin.c" starts at pc 0x63e4 and ends at 0x6404.
  46      </pre>
  47
  48    <p>After <code>info line</code>, the default address for the <code>x</code> command
  49 is changed to the starting address of the line, so that <code>x/i</code> is
  50 sufficient to begin examining the machine code (see <a href="Memory.html#Memory">Examining memory</a>).  Also, this address is saved as the value of the
  51 convenience variable <code>$_</code> (see <a href="Convenience-Vars.html#Convenience%20Vars">Convenience variables</a>).
  52
  53      <dl>
  54 <dt><code>disassemble</code>
  55      <dd>This specialized command dumps a range of memory as machine
  56 instructions.  The default memory range is the function surrounding the
  57 program counter of the selected frame.  A single argument to this
  58 command is a program counter value; GDB dumps the function
  59 surrounding this value.  Two arguments specify a range of addresses
  60 (first inclusive, second exclusive) to dump.
  61 </dl>
  62
  63    <p>The following example shows the disassembly of a range of addresses of
  64 HP PA-RISC 2.0 code:
  65
  66 <pre class="smallexample">     (gdb) disas 0x32c4 0x32e4
  67      Dump of assembler code from 0x32c4 to 0x32e4:
  68      0x32c4 &lt;main+204&gt;:      addil 0,dp
  69      0x32c8 &lt;main+208&gt;:      ldw 0x22c(sr0,r1),r26
  70      0x32cc &lt;main+212&gt;:      ldil 0x3000,r31
  71      0x32d0 &lt;main+216&gt;:      ble 0x3f8(sr4,r31)
  72      0x32d4 &lt;main+220&gt;:      ldo 0(r31),rp
  73      0x32d8 &lt;main+224&gt;:      addil -0x800,dp
  74      0x32dc &lt;main+228&gt;:      ldo 0x588(r1),r26
  75      0x32e0 &lt;main+232&gt;:      ldil 0x3000,r31
  76      End of assembler dump.
  77      </pre>
  78
  79    <p>Some architectures have more than one commonly-used set of instruction
  80 mnemonics or other syntax.
  81
  82      <dl>
  83 <dt><code>set disassembly-flavor </code><var>instruction-set</var><code></code>
  84      <dd>Select the instruction set to use when disassembling the
  85 program via the <code>disassemble</code> or <code>x/i</code> commands.
  86
  87      <p>Currently this command is only defined for the Intel x86 family.  You
  88 can set <var>instruction-set</var> to either <code>intel</code> or <code>att</code>.
  89 The default is <code>att</code>, the AT&amp;T flavor used by default by Unix
  90 assemblers for x86-based targets.
  91 </dl>
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