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  1. <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">

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  18. <title>File-I/O Overview (Debugging with GDB)</title>

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  27. <link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">

  28. <link href="File_002dI_002fO-Remote-Protocol-Extension.html#File_002dI_002fO-Remote-Protocol-Extension" rel="up" title="File-I/O Remote Protocol Extension">

  29. <link href="Protocol-Basics.html#Protocol-Basics" rel="next" title="Protocol Basics">

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  62. <body lang="en">

  63. <a name="File_002dI_002fO-Overview"></a>

  64. <div class="header">

  65. <p>

  66. Next: <a href="Protocol-Basics.html#Protocol-Basics" accesskey="n" rel="next">Protocol Basics</a>, Up: <a href="File_002dI_002fO-Remote-Protocol-Extension.html#File_002dI_002fO-Remote-Protocol-Extension" accesskey="u" rel="up">File-I/O Remote Protocol Extension</a> &nbsp; [<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>

  67. </div>

  68. <hr>

  69. <a name="File_002dI_002fO-Overview-1"></a>

  70. <h4 class="subsection">E.13.1 File-I/O Overview</h4>

  71. <a name="index-file_002di_002fo-overview"></a>

  72. 

  73. <p>The <em>File I/O remote protocol extension</em> (short: File-I/O) allows the

  74. target to use the host&rsquo;s file system and console I/O to perform various

  75. system calls.  System calls on the target system are translated into a

  76. remote protocol packet to the host system, which then performs the needed

  77. actions and returns a response packet to the target system.

  78. This simulates file system operations even on targets that lack file systems.

  79. </p>

  80. <p>The protocol is defined to be independent of both the host and target systems.

  81. It uses its own internal representation of datatypes and values.  Both

  82. <small>GDB</small> and the target&rsquo;s <small>GDB</small> stub are responsible for

  83. translating the system-dependent value representations into the internal

  84. protocol representations when data is transmitted.

  85. </p>

  86. <p>The communication is synchronous.  A system call is possible only when 

  87. <small>GDB</small> is waiting for a response from the &lsquo;<samp>C</samp>&rsquo;, &lsquo;<samp>c</samp>&rsquo;, &lsquo;<samp>S</samp>&rsquo; 

  88. or &lsquo;<samp>s</samp>&rsquo; packets.  While <small>GDB</small> handles the request for a system call,

  89. the target is stopped to allow deterministic access to the target&rsquo;s

  90. memory.  Therefore File-I/O is not interruptible by target signals.  On

  91. the other hand, it is possible to interrupt File-I/O by a user interrupt 

  92. (&lsquo;<samp>Ctrl-C</samp>&rsquo;) within <small>GDB</small>.

  93. </p>

  94. <p>The target&rsquo;s request to perform a host system call does not finish

  95. the latest &lsquo;<samp>C</samp>&rsquo;, &lsquo;<samp>c</samp>&rsquo;, &lsquo;<samp>S</samp>&rsquo; or &lsquo;<samp>s</samp>&rsquo; action.  That means,

  96. after finishing the system call, the target returns to continuing the

  97. previous activity (continue, step).  No additional continue or step

  98. request from <small>GDB</small> is required.

  99. </p>

  100. <div class="smallexample">

  101. <pre class="smallexample">(gdb) continue

  102.   &lt;- target requests 'system call X'

  103.   target is stopped, GDB executes system call

  104.   -&gt; GDB returns result

  105.   ... target continues, GDB returns to wait for the target

  106.   &lt;- target hits breakpoint and sends a Txx packet

  107. </pre></div>

  108. 

  109. <p>The protocol only supports I/O on the console and to regular files on 

  110. the host file system.  Character or block special devices, pipes,

  111. named pipes, sockets or any other communication method on the host

  112. system are not supported by this protocol.

  113. </p>

  114. <p>File I/O is not supported in non-stop mode.

  115. </p>

  116. <hr>

  117. <div class="header">

  118. <p>

  119. Next: <a href="Protocol-Basics.html#Protocol-Basics" accesskey="n" rel="next">Protocol Basics</a>, Up: <a href="File_002dI_002fO-Remote-Protocol-Extension.html#File_002dI_002fO-Remote-Protocol-Extension" accesskey="u" rel="up">File-I/O Remote Protocol Extension</a> &nbsp; [<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>

  120. </div>

  121. 

  122. 

  123. 

  124. </body>

  125. </html>