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diff --git a/share/doc/gdb/i386.html b/share/doc/gdb/i386.html new file mode 100644 index 0000000..6bea2f5 --- /dev/null +++ b/share/doc/gdb/i386.html @@ -0,0 +1,195 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> +<html> +<!-- Copyright (C) 1988-2023 Free Software Foundation, Inc. + +Permission is granted to copy, distribute and/or modify this document +under the terms of the GNU Free Documentation License, Version 1.3 or +any later version published by the Free Software Foundation; with the +Invariant Sections being "Free Software" and "Free Software Needs +Free Documentation", with the Front-Cover Texts being "A GNU Manual," +and with the Back-Cover Texts as in (a) below. + +(a) The FSF's Back-Cover Text is: "You are free to copy and modify +this GNU Manual. Buying copies from GNU Press supports the FSF in +developing GNU and promoting software freedom." --> +<!-- Created by GNU Texinfo 5.1, http://www.gnu.org/software/texinfo/ --> +<head> +<title>Debugging with GDB: i386</title> + +<meta name="description" content="Debugging with GDB: i386"> +<meta name="keywords" content="Debugging with GDB: i386"> +<meta name="resource-type" content="document"> +<meta name="distribution" content="global"> +<meta name="Generator" content="makeinfo"> +<meta http-equiv="Content-Type" content="text/html; charset=utf-8"> +<link href="index.html#Top" rel="start" title="Top"> +<link href="Concept-Index.html#Concept-Index" rel="index" title="Concept Index"> +<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents"> +<link href="Architectures.html#Architectures" rel="up" title="Architectures"> +<link href="Alpha.html#Alpha" rel="next" title="Alpha"> +<link href="AArch64.html#AArch64" rel="previous" title="AArch64"> +<style type="text/css"> +<!-- +a.summary-letter {text-decoration: none} +blockquote.smallquotation {font-size: smaller} +div.display {margin-left: 3.2em} +div.example {margin-left: 3.2em} +div.indentedblock {margin-left: 3.2em} +div.lisp {margin-left: 3.2em} +div.smalldisplay {margin-left: 3.2em} +div.smallexample {margin-left: 3.2em} +div.smallindentedblock {margin-left: 3.2em; font-size: smaller} +div.smalllisp {margin-left: 3.2em} +kbd {font-style:oblique} +pre.display {font-family: inherit} +pre.format {font-family: inherit} +pre.menu-comment {font-family: serif} +pre.menu-preformatted {font-family: serif} +pre.smalldisplay {font-family: inherit; font-size: smaller} +pre.smallexample {font-size: smaller} +pre.smallformat {font-family: inherit; font-size: smaller} +pre.smalllisp {font-size: smaller} +span.nocodebreak {white-space:nowrap} +span.nolinebreak {white-space:nowrap} +span.roman {font-family:serif; font-weight:normal} +span.sansserif {font-family:sans-serif; font-weight:normal} +ul.no-bullet {list-style: none} +--> +</style> + + +</head> + +<body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000"> +<a name="i386"></a> +<div class="header"> +<p> +Next: <a href="Alpha.html#Alpha" accesskey="n" rel="next">Alpha</a>, Previous: <a href="AArch64.html#AArch64" accesskey="p" rel="previous">AArch64</a>, Up: <a href="Architectures.html#Architectures" accesskey="u" rel="up">Architectures</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> +</div> +<hr> +<a name="x86-Architecture_002dspecific-Issues"></a> +<h4 class="subsection">21.4.2 x86 Architecture-specific Issues</h4> + +<dl compact="compact"> +<dt><code>set struct-convention <var>mode</var></code></dt> +<dd><a name="index-set-struct_002dconvention"></a> +<a name="index-struct-return-convention"></a> +<a name="index-struct_002funion-returned-in-registers"></a> +<p>Set the convention used by the inferior to return <code>struct</code>s and +<code>union</code>s from functions to <var>mode</var>. Possible values of +<var>mode</var> are <code>"pcc"</code>, <code>"reg"</code>, and <code>"default"</code> (the +default). <code>"default"</code> or <code>"pcc"</code> means that <code>struct</code>s +are returned on the stack, while <code>"reg"</code> means that a +<code>struct</code> or a <code>union</code> whose size is 1, 2, 4, or 8 bytes will +be returned in a register. +</p> +</dd> +<dt><code>show struct-convention</code></dt> +<dd><a name="index-show-struct_002dconvention"></a> +<p>Show the current setting of the convention to return <code>struct</code>s +from functions. +</p></dd> +</dl> + + +<a name="Intel-Memory-Protection-Extensions-_0028MPX_0029_002e"></a> +<h4 class="subsubsection">21.4.2.1 Intel <em>Memory Protection Extensions</em> (MPX).</h4> +<a name="index-Intel-Memory-Protection-Extensions-_0028MPX_0029_002e"></a> + +<p>Memory Protection Extension (MPX) adds the bound registers ‘<samp>BND0</samp>’ +<a name="DOCF17" href="#FOOT17"><sup>17</sup></a> through ‘<samp>BND3</samp>’. Bound registers store a pair of 64-bit values +which are the lower bound and upper bound. Bounds are effective addresses or +memory locations. The upper bounds are architecturally represented in 1’s +complement form. A bound having lower bound = 0, and upper bound = 0 +(1’s complement of all bits set) will allow access to the entire address space. +</p> +<p>‘<samp>BND0</samp>’ through ‘<samp>BND3</samp>’ are represented in <small>GDB</small> as ‘<samp>bnd0raw</samp>’ +through ‘<samp>bnd3raw</samp>’. Pseudo registers ‘<samp>bnd0</samp>’ through ‘<samp>bnd3</samp>’ +display the upper bound performing the complement of one operation on the +upper bound value, i.e. when upper bound in ‘<samp>bnd0raw</samp>’ is 0 in the +<small>GDB</small> ‘<samp>bnd0</samp>’ it will be <code>0xfff…</code>. In this sense it +can also be noted that the upper bounds are inclusive. +</p> +<p>As an example, assume that the register BND0 holds bounds for a pointer having +access allowed for the range between 0x32 and 0x71. The values present on +bnd0raw and bnd registers are presented as follows: +</p> +<div class="smallexample"> +<pre class="smallexample"> bnd0raw = {0x32, 0xffffffff8e} + bnd0 = {lbound = 0x32, ubound = 0x71} : size 64 +</pre></div> + +<p>This way the raw value can be accessed via bnd0raw…bnd3raw. Any +change on bnd0…bnd3 or bnd0raw…bnd3raw is reflect on its +counterpart. When the bnd0…bnd3 registers are displayed via +Python, the display includes the memory size, in bits, accessible to +the pointer. +</p> +<p>Bounds can also be stored in bounds tables, which are stored in +application memory. These tables store bounds for pointers by specifying +the bounds pointer’s value along with its bounds. Evaluating and changing +bounds located in bound tables is therefore interesting while investigating +bugs on MPX context. <small>GDB</small> provides commands for this purpose: +</p> +<dl compact="compact"> +<dt><code>show mpx bound <var>pointer</var></code></dt> +<dd><a name="index-show-mpx-bound"></a> +<p>Display bounds of the given <var>pointer</var>. +</p> +</dd> +<dt><code>set mpx bound <var>pointer</var>, <var>lbound</var>, <var>ubound</var></code></dt> +<dd><a name="index-set-mpx-bound"></a> +<p>Set the bounds of a pointer in the bound table. +This command takes three parameters: <var>pointer</var> is the pointers +whose bounds are to be changed, <var>lbound</var> and <var>ubound</var> are new values +for lower and upper bounds respectively. +</p></dd> +</dl> + +<p>When you call an inferior function on an Intel MPX enabled program, +GDB sets the inferior’s bound registers to the init (disabled) state +before calling the function. As a consequence, bounds checks for the +pointer arguments passed to the function will always pass. +</p> +<p>This is necessary because when you call an inferior function, the +program is usually in the middle of the execution of other function. +Since at that point bound registers are in an arbitrary state, not +clearing them would lead to random bound violations in the called +function. +</p> +<p>You can still examine the influence of the bound registers on the +execution of the called function by stopping the execution of the +called function at its prologue, setting bound registers, and +continuing the execution. For example: +</p> +<div class="smallexample"> +<pre class="smallexample"> $ break *upper + Breakpoint 2 at 0x4009de: file i386-mpx-call.c, line 47. + $ print upper (a, b, c, d, 1) + Breakpoint 2, upper (a=0x0, b=0x6e0000005b, c=0x0, d=0x0, len=48).... + $ print $bnd0 + {lbound = 0x0, ubound = ffffffff} : size -1 +</pre></div> + +<p>At this last step the value of bnd0 can be changed for investigation of bound +violations caused along the execution of the call. In order to know how to +set the bound registers or bound table for the call consult the ABI. +</p> +<div class="footnote"> +<hr> +<h4 class="footnotes-heading">Footnotes</h4> + +<h3><a name="FOOT17" href="#DOCF17">(17)</a></h3> +<p>The register named with capital letters represent the architecture +registers.</p> +</div> +<hr> +<div class="header"> +<p> +Next: <a href="Alpha.html#Alpha" accesskey="n" rel="next">Alpha</a>, Previous: <a href="AArch64.html#AArch64" accesskey="p" rel="previous">AArch64</a>, Up: <a href="Architectures.html#Architectures" accesskey="u" rel="up">Architectures</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> +</div> + + + +</body> +</html> |