142 lines
6.3 KiB
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142 lines
6.3 KiB
HTML
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<title>Searching Memory - Debugging with GDB</title>
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<a name="Searching-Memory"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="Value-Sizes.html#Value-Sizes">Value Sizes</a>,
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Previous: <a rel="previous" accesskey="p" href="Caching-Target-Data.html#Caching-Target-Data">Caching Target Data</a>,
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Up: <a rel="up" accesskey="u" href="Data.html#Data">Data</a>
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</div>
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<h3 class="section">10.22 Search Memory</h3>
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<p><a name="index-searching-memory-830"></a>
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Memory can be searched for a particular sequence of bytes with the
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<code>find</code> command.
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<a name="index-find-831"></a>
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<dl><dt><code>find </code><span class="roman">[</span><code>/</code><var>sn</var><span class="roman">]</span> <var>start_addr</var><code>, +</code><var>len</var><code>, </code><var>val1</var> <span class="roman">[</span><code>, </code><var>val2</var><code>, ...</code><span class="roman">]</span><dt><code>find </code><span class="roman">[</span><code>/</code><var>sn</var><span class="roman">]</span> <var>start_addr</var><code>, </code><var>end_addr</var><code>, </code><var>val1</var> <span class="roman">[</span><code>, </code><var>val2</var><code>, ...</code><span class="roman">]</span><dd>Search memory for the sequence of bytes specified by <var>val1</var>, <var>val2</var>,
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etc. The search begins at address <var>start_addr</var> and continues for either
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<var>len</var> bytes or through to <var>end_addr</var> inclusive.
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</dl>
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<p><var>s</var> and <var>n</var> are optional parameters.
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They may be specified in either order, apart or together.
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<dl>
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<dt><var>s</var><span class="roman">, search query size</span><dd>The size of each search query value.
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<dl>
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<dt><code>b</code><dd>bytes
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<br><dt><code>h</code><dd>halfwords (two bytes)
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<br><dt><code>w</code><dd>words (four bytes)
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<br><dt><code>g</code><dd>giant words (eight bytes)
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</dl>
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<p>All values are interpreted in the current language.
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This means, for example, that if the current source language is C/C<tt>++</tt>
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then searching for the string “hello” includes the trailing '\0'.
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The null terminator can be removed from searching by using casts,
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e.g.: ‘<samp><span class="samp">{char[5]}"hello"</span></samp>’.
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<p>If the value size is not specified, it is taken from the
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value's type in the current language.
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This is useful when one wants to specify the search
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pattern as a mixture of types.
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Note that this means, for example, that in the case of C-like languages
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a search for an untyped 0x42 will search for ‘<samp><span class="samp">(int) 0x42</span></samp>’
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which is typically four bytes.
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<br><dt><var>n</var><span class="roman">, maximum number of finds</span><dd>The maximum number of matches to print. The default is to print all finds.
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</dl>
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<p>You can use strings as search values. Quote them with double-quotes
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(<code>"</code>).
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The string value is copied into the search pattern byte by byte,
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regardless of the endianness of the target and the size specification.
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<p>The address of each match found is printed as well as a count of the
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number of matches found.
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<p>The address of the last value found is stored in convenience variable
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‘<samp><span class="samp">$_</span></samp>’.
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A count of the number of matches is stored in ‘<samp><span class="samp">$numfound</span></samp>’.
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<p>For example, if stopped at the <code>printf</code> in this function:
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<pre class="smallexample"> void
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hello ()
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{
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static char hello[] = "hello-hello";
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static struct { char c; short s; int i; }
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__attribute__ ((packed)) mixed
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= { 'c', 0x1234, 0x87654321 };
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printf ("%s\n", hello);
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}
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</pre>
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<p class="noindent">you get during debugging:
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<pre class="smallexample"> (gdb) find &hello[0], +sizeof(hello), "hello"
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0x804956d <hello.1620+6>
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1 pattern found
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(gdb) find &hello[0], +sizeof(hello), 'h', 'e', 'l', 'l', 'o'
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0x8049567 <hello.1620>
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0x804956d <hello.1620+6>
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2 patterns found.
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(gdb) find &hello[0], +sizeof(hello), {char[5]}"hello"
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0x8049567 <hello.1620>
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0x804956d <hello.1620+6>
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2 patterns found.
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(gdb) find /b1 &hello[0], +sizeof(hello), 'h', 0x65, 'l'
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0x8049567 <hello.1620>
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1 pattern found
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(gdb) find &mixed, +sizeof(mixed), (char) 'c', (short) 0x1234, (int) 0x87654321
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0x8049560 <mixed.1625>
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1 pattern found
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(gdb) print $numfound
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$1 = 1
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(gdb) print $_
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$2 = (void *) 0x8049560
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</pre>
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</body></html>
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