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
(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).
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.