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| Next: <a href="Debug-Session.html#Debug-Session" accesskey="n" rel="next">Debug Session</a>, Previous: <a href="Stub-Contents.html#Stub-Contents" accesskey="p" rel="prev">Stub Contents</a>, Up: <a href="Remote-Stub.html#Remote-Stub" accesskey="u" rel="up">Remote Stub</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="What-You-Must-Do-for-the-Stub"></a> |
| <h4 class="subsection">20.5.2 What You Must Do for the Stub</h4> |
| |
| <a name="index-remote-stub_002c-support-routines"></a> |
| <p>The debugging stubs that come with <small>GDB</small> are set up for a particular |
| chip architecture, but they have no information about the rest of your |
| debugging target machine. |
| </p> |
| <p>First of all you need to tell the stub how to communicate with the |
| serial port. |
| </p> |
| <dl compact="compact"> |
| <dt><code>int getDebugChar()</code></dt> |
| <dd><a name="index-getDebugChar"></a> |
| <p>Write this subroutine to read a single character from the serial port. |
| It may be identical to <code>getchar</code> for your target system; a |
| different name is used to allow you to distinguish the two if you wish. |
| </p> |
| </dd> |
| <dt><code>void putDebugChar(int)</code></dt> |
| <dd><a name="index-putDebugChar"></a> |
| <p>Write this subroutine to write a single character to the serial port. |
| It may be identical to <code>putchar</code> for your target system; a |
| different name is used to allow you to distinguish the two if you wish. |
| </p></dd> |
| </dl> |
| |
| <a name="index-control-C_002c-and-remote-debugging"></a> |
| <a name="index-interrupting-remote-targets"></a> |
| <p>If you want <small>GDB</small> to be able to stop your program while it is |
| running, you need to use an interrupt-driven serial driver, and arrange |
| for it to stop when it receives a <code>^C</code> (‘<samp>\003</samp>’, the control-C |
| character). That is the character which <small>GDB</small> uses to tell the |
| remote system to stop. |
| </p> |
| <p>Getting the debugging target to return the proper status to <small>GDB</small> |
| probably requires changes to the standard stub; one quick and dirty way |
| is to just execute a breakpoint instruction (the “dirty” part is that |
| <small>GDB</small> reports a <code>SIGTRAP</code> instead of a <code>SIGINT</code>). |
| </p> |
| <p>Other routines you need to supply are: |
| </p> |
| <dl compact="compact"> |
| <dt><code>void exceptionHandler (int <var>exception_number</var>, void *<var>exception_address</var>)</code></dt> |
| <dd><a name="index-exceptionHandler"></a> |
| <p>Write this function to install <var>exception_address</var> in the exception |
| handling tables. You need to do this because the stub does not have any |
| way of knowing what the exception handling tables on your target system |
| are like (for example, the processor’s table might be in <small>ROM</small>, |
| containing entries which point to a table in <small>RAM</small>). |
| The <var>exception_number</var> specifies the exception which should be changed; |
| its meaning is architecture-dependent (for example, different numbers |
| might represent divide by zero, misaligned access, etc). When this |
| exception occurs, control should be transferred directly to |
| <var>exception_address</var>, and the processor state (stack, registers, |
| and so on) should be just as it is when a processor exception occurs. So if |
| you want to use a jump instruction to reach <var>exception_address</var>, it |
| should be a simple jump, not a jump to subroutine. |
| </p> |
| <p>For the 386, <var>exception_address</var> should be installed as an interrupt |
| gate so that interrupts are masked while the handler runs. The gate |
| should be at privilege level 0 (the most privileged level). The |
| <small>SPARC</small> and 68k stubs are able to mask interrupts themselves without |
| help from <code>exceptionHandler</code>. |
| </p> |
| </dd> |
| <dt><code>void flush_i_cache()</code></dt> |
| <dd><a name="index-flush_005fi_005fcache"></a> |
| <p>On <small>SPARC</small> and <small>SPARCLITE</small> only, write this subroutine to flush the |
| instruction cache, if any, on your target machine. If there is no |
| instruction cache, this subroutine may be a no-op. |
| </p> |
| <p>On target machines that have instruction caches, <small>GDB</small> requires this |
| function to make certain that the state of your program is stable. |
| </p></dd> |
| </dl> |
| |
| <p>You must also make sure this library routine is available: |
| </p> |
| <dl compact="compact"> |
| <dt><code>void *memset(void *, int, int)</code></dt> |
| <dd><a name="index-memset"></a> |
| <p>This is the standard library function <code>memset</code> that sets an area of |
| memory to a known value. If you have one of the free versions of |
| <code>libc.a</code>, <code>memset</code> can be found there; otherwise, you must |
| either obtain it from your hardware manufacturer, or write your own. |
| </p></dd> |
| </dl> |
| |
| <p>If you do not use the GNU C compiler, you may need other standard |
| library subroutines as well; this varies from one stub to another, |
| but in general the stubs are likely to use any of the common library |
| subroutines which <code><small>GCC</small></code> generates as inline code. |
| </p> |
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| Next: <a href="Debug-Session.html#Debug-Session" accesskey="n" rel="next">Debug Session</a>, Previous: <a href="Stub-Contents.html#Stub-Contents" accesskey="p" rel="prev">Stub Contents</a>, Up: <a href="Remote-Stub.html#Remote-Stub" accesskey="u" rel="up">Remote Stub</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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