10.23 Search Memory

Memory can be searched for a particular sequence of bytes with the find command.

find [/sn] start_addr, +len, val1 [, val2, …]

find [/sn] start_addr, end_addr, val1 [, val2, …]

Search memory for the sequence of bytes specified by val1, val2, etc. The search begins at address start_addr and continues for either len bytes or through to end_addr inclusive.

s and n are optional parameters. They may be specified in either order, apart or together.

s, search query size

The size of each search query value.

b

bytes

h

halfwords (two bytes)

w

words (four bytes)

g

giant words (eight bytes)

All values are interpreted in the current language. This means, for example, that if the current source language is C/C++ then searching for the string “hello” includes the trailing ’\0’. The null terminator can be removed from searching by using casts, e.g.: ‘{char[5]}"hello"’.

If the value size is not specified, it is taken from the value’s type in the current language. This is useful when one wants to specify the search pattern as a mixture of types. Note that this means, for example, that in the case of C-like languages a search for an untyped 0x42 will search for ‘(int) 0x42’ which is typically four bytes.

n, maximum number of finds

The maximum number of matches to print. The default is to print all finds.

You can use strings as search values. Quote them with double-quotes ("). The string value is copied into the search pattern byte by byte, regardless of the endianness of the target and the size specification.

The address of each match found is printed as well as a count of the number of matches found.

The address of the last value found is stored in convenience variable ‘$_’. A count of the number of matches is stored in ‘$numfound’.

For example, if stopped at the printf in this function:

void
hello ()
{
  static char hello[] = "hello-hello";
  static struct { char c; short s; int i; }
    __attribute__ ((packed)) mixed
    = { 'c', 0x1234, 0x87654321 };
  printf ("%s\n", hello);
}

you get during debugging:

(gdb) find &hello[0], +sizeof(hello), "hello"
0x804956d <hello.1620+6>
1 pattern found
(gdb) find &hello[0], +sizeof(hello), 'h', 'e', 'l', 'l', 'o'
0x8049567 <hello.1620>
0x804956d <hello.1620+6>
2 patterns found.
(gdb) find &hello[0], +sizeof(hello), {char[5]}"hello"
0x8049567 <hello.1620>
0x804956d <hello.1620+6>
2 patterns found.
(gdb) find /b1 &hello[0], +sizeof(hello), 'h', 0x65, 'l'
0x8049567 <hello.1620>
1 pattern found
(gdb) find &mixed, +sizeof(mixed), (char) 'c', (short) 0x1234, (int) 0x87654321
0x8049560 <mixed.1625>
1 pattern found
(gdb) print $numfound
$1 = 1
(gdb) print $_
$2 = (void *) 0x8049560