Red Hat ENTERPRISE LINUX 4 - DEVELOPER TOOLS GUIDE, Manual

Page: 73 / 410

Chapter 9. Examining Source Files 63
9.5. 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 (refer to Section 9.1
Printing source lines ).
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 (refer to Section 10.5 Examining
memory ). Also, this address is saved as the value of the convenience variable
$_
(refer to Section 10.9
Convenience variables ).
disassemble
This specialized command dumps a range of memory as machine instructions. The default mem-
ory range is the function surrounding the program counter of the selected frame. A single ar-
gument 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.