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 now 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_changecom
     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 (see Examining memory: Memory.).  Also, this address is saved as the value of the convenience
variable `$_' (see Convenience variables: Convenience Vars.).

`disassemble'
     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.

   We can use `disassemble' to inspect the object code range shown in
the last `info line' example (the example shows SPARC machine
instructions):

     (gdb) disas 0x63e4 0x6404
     Dump of assembler code from 0x63e4 to 0x6404:
     0x63e4 <builtin_init+5340>:     ble 0x63f8 <builtin_init+5360>
     0x63e8 <builtin_init+5344>:     sethi %hi(0x4c00), %o0
     0x63ec <builtin_init+5348>:     ld [%i1+4], %o0
     0x63f0 <builtin_init+5352>:     b 0x63fc <builtin_init+5364>
     0x63f4 <builtin_init+5356>:     ld [%o0+4], %o0
     0x63f8 <builtin_init+5360>:     or %o0, 0x1a4, %o0
     0x63fc <builtin_init+5364>:     call 0x9288 <path_search>
     0x6400 <builtin_init+5368>:     nop
     End of assembler dump.