126 lines
6.7 KiB
HTML
126 lines
6.7 KiB
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<html lang="en">
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<head>
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<title>Bootstrapping - Debugging with GDB</title>
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<meta name="description" content="Debugging with GDB">
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<meta name="generator" content="makeinfo 4.13">
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<link title="Top" rel="start" href="index.html#Top">
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<link rel="up" href="Remote-Stub.html#Remote-Stub" title="Remote Stub">
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<link rel="prev" href="Stub-Contents.html#Stub-Contents" title="Stub Contents">
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<link rel="next" href="Debug-Session.html#Debug-Session" title="Debug Session">
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<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage">
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Copyright (C) 1988-2019 Free Software Foundation, Inc.
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3 or
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any later version published by the Free Software Foundation; with the
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Invariant Sections being ``Free Software'' and ``Free Software Needs
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Free Documentation'', with the Front-Cover Texts being ``A GNU Manual,''
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and with the Back-Cover Texts as in (a) below.
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(a) The FSF's Back-Cover Text is: ``You are free to copy and modify
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this GNU Manual. Buying copies from GNU Press supports the FSF in
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</head>
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<body>
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<div class="node">
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<a name="Bootstrapping"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="Debug-Session.html#Debug-Session">Debug Session</a>,
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Previous: <a rel="previous" accesskey="p" href="Stub-Contents.html#Stub-Contents">Stub Contents</a>,
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Up: <a rel="up" accesskey="u" href="Remote-Stub.html#Remote-Stub">Remote Stub</a>
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<hr>
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</div>
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<h4 class="subsection">20.5.2 What You Must Do for the Stub</h4>
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<p><a name="index-remote-stub_002c-support-routines-1430"></a>The debugging stubs that come with <span class="sc">gdb</span> are set up for a particular
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chip architecture, but they have no information about the rest of your
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debugging target machine.
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<p>First of all you need to tell the stub how to communicate with the
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serial port.
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<dl>
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<dt><code>int getDebugChar()</code><dd><a name="index-getDebugChar-1431"></a>Write this subroutine to read a single character from the serial port.
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It may be identical to <code>getchar</code> for your target system; a
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different name is used to allow you to distinguish the two if you wish.
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<br><dt><code>void putDebugChar(int)</code><dd><a name="index-putDebugChar-1432"></a>Write this subroutine to write a single character to the serial port.
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It may be identical to <code>putchar</code> for your target system; a
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different name is used to allow you to distinguish the two if you wish.
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</dl>
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<p><a name="index-control-C_002c-and-remote-debugging-1433"></a><a name="index-interrupting-remote-targets-1434"></a>If you want <span class="sc">gdb</span> to be able to stop your program while it is
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running, you need to use an interrupt-driven serial driver, and arrange
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for it to stop when it receives a <code>^C</code> (‘<samp><span class="samp">\003</span></samp>’, the control-C
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character). That is the character which <span class="sc">gdb</span> uses to tell the
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remote system to stop.
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<p>Getting the debugging target to return the proper status to <span class="sc">gdb</span>
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probably requires changes to the standard stub; one quick and dirty way
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is to just execute a breakpoint instruction (the “dirty” part is that
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<span class="sc">gdb</span> reports a <code>SIGTRAP</code> instead of a <code>SIGINT</code>).
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<p>Other routines you need to supply are:
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<dl>
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<dt><code>void exceptionHandler (int </code><var>exception_number</var><code>, void *</code><var>exception_address</var><code>)</code><dd><a name="index-exceptionHandler-1435"></a>Write this function to install <var>exception_address</var> in the exception
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handling tables. You need to do this because the stub does not have any
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way of knowing what the exception handling tables on your target system
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are like (for example, the processor's table might be in <span class="sc">rom</span>,
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containing entries which point to a table in <span class="sc">ram</span>).
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The <var>exception_number</var> specifies the exception which should be changed;
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its meaning is architecture-dependent (for example, different numbers
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might represent divide by zero, misaligned access, etc). When this
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exception occurs, control should be transferred directly to
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<var>exception_address</var>, and the processor state (stack, registers,
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and so on) should be just as it is when a processor exception occurs. So if
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you want to use a jump instruction to reach <var>exception_address</var>, it
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should be a simple jump, not a jump to subroutine.
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<p>For the 386, <var>exception_address</var> should be installed as an interrupt
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gate so that interrupts are masked while the handler runs. The gate
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should be at privilege level 0 (the most privileged level). The
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<span class="sc">sparc</span> and 68k stubs are able to mask interrupts themselves without
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help from <code>exceptionHandler</code>.
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<br><dt><code>void flush_i_cache()</code><dd><a name="index-flush_005fi_005fcache-1436"></a>On <span class="sc">sparc</span> and <span class="sc">sparclite</span> only, write this subroutine to flush the
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instruction cache, if any, on your target machine. If there is no
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instruction cache, this subroutine may be a no-op.
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<p>On target machines that have instruction caches, <span class="sc">gdb</span> requires this
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function to make certain that the state of your program is stable.
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</dl>
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<p class="noindent">You must also make sure this library routine is available:
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<dl>
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<dt><code>void *memset(void *, int, int)</code><dd><a name="index-memset-1437"></a>This is the standard library function <code>memset</code> that sets an area of
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memory to a known value. If you have one of the free versions of
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<code>libc.a</code>, <code>memset</code> can be found there; otherwise, you must
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either obtain it from your hardware manufacturer, or write your own.
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</dl>
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<p>If you do not use the GNU C compiler, you may need other standard
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library subroutines as well; this varies from one stub to another,
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but in general the stubs are likely to use any of the common library
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subroutines which <span class="sc">gcc</span> generates as inline code.
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</body></html>
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