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| <title>Debugging with GDB: Searching Memory</title> |
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| Previous: <a href="Caching-Target-Data.html#Caching-Target-Data" accesskey="p" rel="prev">Caching Target Data</a>, Up: <a href="Data.html#Data" accesskey="u" rel="up">Data</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p> |
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| <a name="Search-Memory"></a> |
| <h3 class="section">10.22 Search Memory</h3> |
| <a name="index-searching-memory"></a> |
| |
| <p>Memory can be searched for a particular sequence of bytes with the |
| <code>find</code> command. |
| </p> |
| <dl compact="compact"> |
| <dd><a name="index-find"></a> |
| </dd> |
| <dt><code>find <span class="roman">[</span>/<var>sn</var><span class="roman">]</span> <var>start_addr</var>, +<var>len</var>, <var>val1</var> <span class="roman">[</span>, <var>val2</var>, …<span class="roman">]</span></code></dt> |
| <dt><code>find <span class="roman">[</span>/<var>sn</var><span class="roman">]</span> <var>start_addr</var>, <var>end_addr</var>, <var>val1</var> <span class="roman">[</span>, <var>val2</var>, …<span class="roman">]</span></code></dt> |
| <dd><p>Search memory for the sequence of bytes specified by <var>val1</var>, <var>val2</var>, |
| etc. The search begins at address <var>start_addr</var> and continues for either |
| <var>len</var> bytes or through to <var>end_addr</var> inclusive. |
| </p></dd> |
| </dl> |
| |
| <p><var>s</var> and <var>n</var> are optional parameters. |
| They may be specified in either order, apart or together. |
| </p> |
| <dl compact="compact"> |
| <dt><span class="roman"><var>s</var>, search query size</span></dt> |
| <dd><p>The size of each search query value. |
| </p> |
| <dl compact="compact"> |
| <dt><code>b</code></dt> |
| <dd><p>bytes |
| </p></dd> |
| <dt><code>h</code></dt> |
| <dd><p>halfwords (two bytes) |
| </p></dd> |
| <dt><code>w</code></dt> |
| <dd><p>words (four bytes) |
| </p></dd> |
| <dt><code>g</code></dt> |
| <dd><p>giant words (eight bytes) |
| </p></dd> |
| </dl> |
| |
| <p>All values are interpreted in the current language. |
| This means, for example, that if the current source language is C/C<tt>++</tt> |
| then searching for the string “hello” includes the trailing ’\0’. |
| </p> |
| <p>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 ‘<samp>(int) 0x42</samp>’ |
| which is typically four bytes. |
| </p> |
| </dd> |
| <dt><span class="roman"><var>n</var>, maximum number of finds</span></dt> |
| <dd><p>The maximum number of matches to print. The default is to print all finds. |
| </p></dd> |
| </dl> |
| |
| <p>You can use strings as search values. Quote them with double-quotes |
| (<code>"</code>). |
| The string value is copied into the search pattern byte by byte, |
| regardless of the endianness of the target and the size specification. |
| </p> |
| <p>The address of each match found is printed as well as a count of the |
| number of matches found. |
| </p> |
| <p>The address of the last value found is stored in convenience variable |
| ‘<samp>$_</samp>’. |
| A count of the number of matches is stored in ‘<samp>$numfound</samp>’. |
| </p> |
| <p>For example, if stopped at the <code>printf</code> in this function: |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">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); |
| } |
| </pre></div> |
| |
| <p>you get during debugging: |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">(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 /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 |
| </pre></div> |
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