133 lines
6.6 KiB
HTML
133 lines
6.6 KiB
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>
|
||
|
|
|