Machine Code

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Source and machine code

You can use the command `info line' to map source lines to program
addresses (and vice versa), and the command `disassemble' to display a
range of addresses as machine instructions.  When run under GNU Emacs
mode, the `info line' command causes the arrow to point to the line
specified.  Also, `info line' prints addresses in symbolic form as well
as hex.
`info line LINESPEC'
     Print the starting and ending addresses of the compiled code for
     source line LINESPEC.  You can specify source lines in any of the
     ways understood by the `list' command (*note Printing source
     lines: List.).
   For example, we can use `info line' to discover the location of the
object code for the first line of function `m4_changequote':
     (gdb) info line m4_changequote
     Line 895 of "builtin.c" starts at pc 0x634c and ends at 0x6350.
We can also inquire (using `*ADDR' as the form for LINESPEC) what
source line covers a particular address:
     (gdb) info line *0x63ff
     Line 926 of "builtin.c" starts at pc 0x63e4 and ends at 0x6404.
   After `info line', the default address for the `x' command is
changed to the starting address of the line, so that `x/i' is
sufficient to begin examining the machine code (*note Examining memory:
Memory.).  Also, this address is saved as the value of the convenience
variable `$_' (*note Convenience variables: Convenience Vars.).
     This specialized command dumps a range of memory as machine
     instructions.  The default memory range is the function
     surrounding the program counter of the selected frame.  A single
     argument to this command is a program counter value; GDB dumps the
     function surrounding this value.  Two arguments specify a range of
     addresses (first inclusive, second exclusive) to dump.
   The following example shows the disassembly of a range of addresses
of HP PA-RISC 2.0 code:
     (gdb) disas 0x32c4 0x32e4
     Dump of assembler code from 0x32c4 to 0x32e4:
     0x32c4 <main+204>:      addil 0,dp
     0x32c8 <main+208>:      ldw 0x22c(sr0,r1),r26
     0x32cc <main+212>:      ldil 0x3000,r31
     0x32d0 <main+216>:      ble 0x3f8(sr4,r31)
     0x32d4 <main+220>:      ldo 0(r31),rp
     0x32d8 <main+224>:      addil -0x800,dp
     0x32dc <main+228>:      ldo 0x588(r1),r26
     0x32e0 <main+232>:      ldil 0x3000,r31
     End of assembler dump.
   Some architectures have more than one commonly-used set of
instruction mnemonics or other syntax.
`set disassembly-flavor INSTRUCTION-SET'
     Select the instruction set to use when disassembling the program
     via the `disassemble' or `x/i' commands.
     Currently this command is only defined for the Intel x86 family.
     You can set INSTRUCTION-SET to either `intel' or `att'.  The
     default is `att', the AT&T flavor used by default by Unix
     assemblers for x86-based targets.