aarch64-linux-gnu-9.2/share/doc/gdb/Ada-Glitches.html - toolchains/linux-x86/gcc - Git at Google

 <html lang="en">
 <head>
 <title>Ada Glitches - Debugging with GDB</title>
 <meta http-equiv="Content-Type" content="text/html">
 <meta name="description" content="Debugging with GDB">
 <meta name="generator" content="makeinfo 4.13">
 <link title="Top" rel="start" href="index.html#Top">
 <link rel="up" href="Ada.html#Ada" title="Ada">
 <link rel="prev" href="Ada-Settings.html#Ada-Settings" title="Ada Settings">
 <link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage">
 <!--
 Copyright (C) 1988-2019 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.''
 -->
 <meta http-equiv="Content-Style-Type" content="text/css">
 <style type="text/css"><!--
   pre.display { font-family:inherit }
   pre.format  { font-family:inherit }
   pre.smalldisplay { font-family:inherit; font-size:smaller }
   pre.smallformat  { font-family:inherit; font-size:smaller }
   pre.smallexample { font-size:smaller }
   pre.smalllisp    { font-size:smaller }
   span.sc    { font-variant:small-caps }
   span.roman { font-family:serif; font-weight:normal; }
   span.sansserif { font-family:sans-serif; font-weight:normal; }
 --></style>
 </head>
 <body>
 <div class="node">
 <a name="Ada-Glitches"></a>
 <p>
 Previous:&nbsp;<a rel="previous" accesskey="p" href="Ada-Settings.html#Ada-Settings">Ada Settings</a>,
 Up:&nbsp;<a rel="up" accesskey="u" href="Ada.html#Ada">Ada</a>
 <hr>
 </div>

 <h5 class="subsubsection">15.4.10.11 Known Peculiarities of Ada Mode</h5>

 <p><a name="index-Ada_002c-problems-1088"></a>
 Besides the omissions listed previously (see <a href="Omissions-from-Ada.html#Omissions-from-Ada">Omissions from Ada</a>),
 we know of several problems with and limitations of Ada mode in
 <span class="sc">gdb</span>,
 some of which will be fixed with planned future releases of the debugger
 and the GNU Ada compiler.

      <ul>
 <li>Static constants that the compiler chooses not to materialize as objects in
 storage are invisible to the debugger.

      <li>Named parameter associations in function argument lists are ignored (the
 argument lists are treated as positional).

      <li>Many useful library packages are currently invisible to the debugger.

      <li>Fixed-point arithmetic, conversions, input, and output is carried out using
 floating-point arithmetic, and may give results that only approximate those on
 the host machine.

      <li>The GNAT compiler never generates the prefix <code>Standard</code> for any of
 the standard symbols defined by the Ada language.  <span class="sc">gdb</span> knows about
 this: it will strip the prefix from names when you use it, and will never
 look for a name you have so qualified among local symbols, nor match against
 symbols in other packages or subprograms.  If you have
 defined entities anywhere in your program other than parameters and
 local variables whose simple names match names in <code>Standard</code>,
 GNAT's lack of qualification here can cause confusion.  When this happens,
 you can usually resolve the confusion
 by qualifying the problematic names with package
 <code>Standard</code> explicitly.
 </ul>

    <p>Older versions of the compiler sometimes generate erroneous debugging
 information, resulting in the debugger incorrectly printing the value
 of affected entities.  In some cases, the debugger is able to work
 around an issue automatically. In other cases, the debugger is able
 to work around the issue, but the work-around has to be specifically
 enabled.

    <p><a name="index-set-ada-trust_002dPAD_002dover_002dXVS-1089"></a><a name="index-show-ada-trust_002dPAD_002dover_002dXVS-1090"></a>
      <dl>
 <dt><code>set ada trust-PAD-over-XVS on</code><dd>Configure GDB to strictly follow the GNAT encoding when computing the
 value of Ada entities, particularly when <code>PAD</code> and <code>PAD___XVS</code>
 types are involved (see <code>ada/exp_dbug.ads</code> in the GCC sources for
 a complete description of the encoding used by the GNAT compiler).
 This is the default.

      <br><dt><code>set ada trust-PAD-over-XVS off</code><dd>This is related to the encoding using by the GNAT compiler.  If <span class="sc">gdb</span>
 sometimes prints the wrong value for certain entities, changing <code>ada
 trust-PAD-over-XVS</code> to <code>off</code> activates a work-around which may fix
 the issue.  It is always safe to set <code>ada trust-PAD-over-XVS</code> to
 <code>off</code>, but this incurs a slight performance penalty, so it is
 recommended to leave this setting to <code>on</code> unless necessary.

    </dl>

    <p><a name="index-GNAT-descriptive-types-1091"></a><a name="index-GNAT-encoding-1092"></a>Internally, the debugger also relies on the compiler following a number
 of conventions known as the &lsquo;<samp><span class="samp">GNAT Encoding</span></samp>&rsquo;, all documented in
 <samp><span class="file">gcc/ada/exp_dbug.ads</span></samp> in the GCC sources. This encoding describes
 how the debugging information should be generated for certain types.
 In particular, this convention makes use of <dfn>descriptive types</dfn>,
 which are artificial types generated purely to help the debugger.

    <p>These encodings were defined at a time when the debugging information
 format used was not powerful enough to describe some of the more complex
 types available in Ada.  Since DWARF allows us to express nearly all
 Ada features, the long-term goal is to slowly replace these descriptive
 types by their pure DWARF equivalent.  To facilitate that transition,
 a new maintenance option is available to force the debugger to ignore
 those descriptive types.  It allows the user to quickly evaluate how
 well <span class="sc">gdb</span> works without them.


 <a name="index-maint-ada-set-ignore_002ddescriptive_002dtypes-1093"></a>
 <dl><dt><code>maintenance ada set ignore-descriptive-types [on|off]</code><dd>Control whether the debugger should ignore descriptive types.
 The default is not to ignore descriptives types (<code>off</code>).

      <p><a name="index-maint-ada-show-ignore_002ddescriptive_002dtypes-1094"></a><br><dt><code>maintenance ada show ignore-descriptive-types</code><dd>Show if descriptive types are ignored by <span class="sc">gdb</span>.

    </dl>

    </body></html>
	<html lang="en">
	<head>
	<title>Ada Glitches - Debugging with GDB</title>
	<meta http-equiv="Content-Type" content="text/html">
	<meta name="description" content="Debugging with GDB">
	<meta name="generator" content="makeinfo 4.13">
	<link title="Top" rel="start" href="index.html#Top">
	<link rel="up" href="Ada.html#Ada" title="Ada">
	<link rel="prev" href="Ada-Settings.html#Ada-Settings" title="Ada Settings">
	<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage">
	<!--
	Copyright (C) 1988-2019 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.''
	-->
	<meta http-equiv="Content-Style-Type" content="text/css">
	<style type="text/css"><!--
	pre.display { font-family:inherit }
	pre.format { font-family:inherit }
	pre.smalldisplay { font-family:inherit; font-size:smaller }
	pre.smallformat { font-family:inherit; font-size:smaller }
	pre.smallexample { font-size:smaller }
	pre.smalllisp { font-size:smaller }
	span.sc { font-variant:small-caps }
	span.roman { font-family:serif; font-weight:normal; }
	span.sansserif { font-family:sans-serif; font-weight:normal; }
	--></style>
	</head>
	<body>
	<div class="node">
	<a name="Ada-Glitches"></a>
	<p>
	Previous: <a rel="previous" accesskey="p" href="Ada-Settings.html#Ada-Settings">Ada Settings</a>,
	Up: <a rel="up" accesskey="u" href="Ada.html#Ada">Ada</a>
	<hr>
	</div>

	<h5 class="subsubsection">15.4.10.11 Known Peculiarities of Ada Mode</h5>

	<p><a name="index-Ada_002c-problems-1088"></a>
	Besides the omissions listed previously (see <a href="Omissions-from-Ada.html#Omissions-from-Ada">Omissions from Ada</a>),
	we know of several problems with and limitations of Ada mode in
	<span class="sc">gdb</span>,
	some of which will be fixed with planned future releases of the debugger
	and the GNU Ada compiler.

	<ul>
	<li>Static constants that the compiler chooses not to materialize as objects in
	storage are invisible to the debugger.

	<li>Named parameter associations in function argument lists are ignored (the
	argument lists are treated as positional).

	<li>Many useful library packages are currently invisible to the debugger.

	<li>Fixed-point arithmetic, conversions, input, and output is carried out using
	floating-point arithmetic, and may give results that only approximate those on
	the host machine.

	<li>The GNAT compiler never generates the prefix <code>Standard</code> for any of
	the standard symbols defined by the Ada language. <span class="sc">gdb</span> knows about
	this: it will strip the prefix from names when you use it, and will never
	look for a name you have so qualified among local symbols, nor match against
	symbols in other packages or subprograms. If you have
	defined entities anywhere in your program other than parameters and
	local variables whose simple names match names in <code>Standard</code>,
	GNAT's lack of qualification here can cause confusion. When this happens,
	you can usually resolve the confusion
	by qualifying the problematic names with package
	<code>Standard</code> explicitly.
	</ul>

	<p>Older versions of the compiler sometimes generate erroneous debugging
	information, resulting in the debugger incorrectly printing the value
	of affected entities. In some cases, the debugger is able to work
	around an issue automatically. In other cases, the debugger is able
	to work around the issue, but the work-around has to be specifically
	enabled.

	<p><a name="index-set-ada-trust_002dPAD_002dover_002dXVS-1089"></a><a name="index-show-ada-trust_002dPAD_002dover_002dXVS-1090"></a>
	<dl>
	<dt><code>set ada trust-PAD-over-XVS on</code><dd>Configure GDB to strictly follow the GNAT encoding when computing the
	value of Ada entities, particularly when <code>PAD</code> and <code>PAD___XVS</code>
	types are involved (see <code>ada/exp_dbug.ads</code> in the GCC sources for
	a complete description of the encoding used by the GNAT compiler).
	This is the default.

	<br><dt><code>set ada trust-PAD-over-XVS off</code><dd>This is related to the encoding using by the GNAT compiler. If <span class="sc">gdb</span>
	sometimes prints the wrong value for certain entities, changing <code>ada
	trust-PAD-over-XVS</code> to <code>off</code> activates a work-around which may fix
	the issue. It is always safe to set <code>ada trust-PAD-over-XVS</code> to
	<code>off</code>, but this incurs a slight performance penalty, so it is
	recommended to leave this setting to <code>on</code> unless necessary.

	</dl>

	<p><a name="index-GNAT-descriptive-types-1091"></a><a name="index-GNAT-encoding-1092"></a>Internally, the debugger also relies on the compiler following a number
	of conventions known as the ‘<samp><span class="samp">GNAT Encoding</span></samp>’, all documented in
	<samp><span class="file">gcc/ada/exp_dbug.ads</span></samp> in the GCC sources. This encoding describes
	how the debugging information should be generated for certain types.
	In particular, this convention makes use of <dfn>descriptive types</dfn>,
	which are artificial types generated purely to help the debugger.

	<p>These encodings were defined at a time when the debugging information
	format used was not powerful enough to describe some of the more complex
	types available in Ada. Since DWARF allows us to express nearly all
	Ada features, the long-term goal is to slowly replace these descriptive
	types by their pure DWARF equivalent. To facilitate that transition,
	a new maintenance option is available to force the debugger to ignore
	those descriptive types. It allows the user to quickly evaluate how
	well <span class="sc">gdb</span> works without them.


	<a name="index-maint-ada-set-ignore_002ddescriptive_002dtypes-1093"></a>
	<dl><dt><code>maintenance ada set ignore-descriptive-types [on\|off]</code><dd>Control whether the debugger should ignore descriptive types.
	The default is not to ignore descriptives types (<code>off</code>).

	<p><a name="index-maint-ada-show-ignore_002ddescriptive_002dtypes-1094"></a><br><dt><code>maintenance ada show ignore-descriptive-types</code><dd>Show if descriptive types are ignored by <span class="sc">gdb</span>.

	</dl>

	</body></html>