1<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> 2<html> 3<!-- Copyright (C) 1988-2021 Free Software Foundation, Inc. 4 5Permission is granted to copy, distribute and/or modify this document 6under the terms of the GNU Free Documentation License, Version 1.3 or 7any later version published by the Free Software Foundation; with the 8Invariant Sections being "Free Software" and "Free Software Needs 9Free Documentation", with the Front-Cover Texts being "A GNU Manual," 10and with the Back-Cover Texts as in (a) below. 11 12(a) The FSF's Back-Cover Text is: "You are free to copy and modify 13this GNU Manual. 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Since a File-I/O system call can only occur when 76<small>GDB</small> is waiting for a response from the continuing or stepping target, 77the File-I/O request is a reply that <small>GDB</small> has to expect as a result 78of a previous ‘<samp>C</samp>’, ‘<samp>c</samp>’, ‘<samp>S</samp>’ or ‘<samp>s</samp>’ packet. 79This <code>F</code> packet contains all information needed to allow <small>GDB</small> 80to call the appropriate host system call: 81</p> 82<ul> 83<li> A unique identifier for the requested system call. 84 85</li><li> All parameters to the system call. Pointers are given as addresses 86in the target memory address space. Pointers to strings are given as 87pointer/length pair. Numerical values are given as they are. 88Numerical control flags are given in a protocol-specific representation. 89 90</li></ul> 91 92<p>At this point, <small>GDB</small> has to perform the following actions. 93</p> 94<ul> 95<li> If the parameters include pointer values to data needed as input to a 96system call, <small>GDB</small> requests this data from the target with a 97standard <code>m</code> packet request. This additional communication has to be 98expected by the target implementation and is handled as any other <code>m</code> 99packet. 100 101</li><li> <small>GDB</small> translates all value from protocol representation to host 102representation as needed. Datatypes are coerced into the host types. 103 104</li><li> <small>GDB</small> calls the system call. 105 106</li><li> It then coerces datatypes back to protocol representation. 107 108</li><li> If the system call is expected to return data in buffer space specified 109by pointer parameters to the call, the data is transmitted to the 110target using a <code>M</code> or <code>X</code> packet. This packet has to be expected 111by the target implementation and is handled as any other <code>M</code> or <code>X</code> 112packet. 113 114</li></ul> 115 116<p>Eventually <small>GDB</small> replies with another <code>F</code> packet which contains all 117necessary information for the target to continue. This at least contains 118</p> 119<ul> 120<li> Return value. 121 122</li><li> <code>errno</code>, if has been changed by the system call. 123 124</li><li> “Ctrl-C” flag. 125 126</li></ul> 127 128<p>After having done the needed type and value coercion, the target continues 129the latest continue or step action. 130</p> 131<hr> 132<div class="header"> 133<p> 134Next: <a href="The-F-Request-Packet.html#The-F-Request-Packet" accesskey="n" rel="next">The F Request Packet</a>, Previous: <a href="File_002dI_002fO-Overview.html#File_002dI_002fO-Overview" accesskey="p" rel="previous">File-I/O Overview</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> [<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> 135</div> 136 137 138 139</body> 140</html> 141