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Written by: Lionel Cons <Lionel.Cons@cern.ch> (original author)
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Olaf Bachmann <obachman@mathematik.uni-kl.de>
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Maintained by: Olaf Bachmann <obachman@mathematik.uni-kl.de>
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<HEAD>
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<TITLE>GDB Internals: Overall Structure</TITLE>
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<TR><TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdbint_1.html#SEC1"> < </A>]</TD>
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<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdbint_toc.html#SEC_Contents">Contents</A>]</TD>
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<H1> 2. Overall Structure </H1>
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<!--docid::SEC2::-->
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<P>
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GDB consists of three major subsystems: user interface,
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symbol handling (the <EM>symbol side</EM>), and target system handling (the
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<EM>target side</EM>).
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</P><P>
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The user interface consists of several actual interfaces, plus
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supporting code.
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</P><P>
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The symbol side consists of object file readers, debugging info
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interpreters, symbol table management, source language expression
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parsing, type and value printing.
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</P><P>
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The target side consists of execution control, stack frame analysis, and
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physical target manipulation.
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</P><P>
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The target side/symbol side division is not formal, and there are a
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number of exceptions. For instance, core file support involves symbolic
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elements (the basic core file reader is in BFD) and target elements (it
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supplies the contents of memory and the values of registers). Instead,
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this division is useful for understanding how the minor subsystems
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should fit together.
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</P><P>
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<HR SIZE="6">
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<A NAME="SEC3"></A>
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<TABLE CELLPADDING=1 CELLSPACING=1 BORDER=0>
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<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdbint_toc.html#SEC_Contents">Contents</A>]</TD>
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<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdbint_19.html#SEC186">Index</A>]</TD>
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<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdbint_abt.html#SEC_About"> ? </A>]</TD>
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</TR></TABLE>
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<H2> 2.1 The Symbol Side </H2>
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<!--docid::SEC3::-->
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<P>
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The symbolic side of GDB can be thought of as "everything
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you can do in GDB without having a live program running".
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For instance, you can look at the types of variables, and evaluate
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many kinds of expressions.
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</P><P>
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<HR SIZE="6">
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<A NAME="SEC4"></A>
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<TABLE CELLPADDING=1 CELLSPACING=1 BORDER=0>
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<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdbint_toc.html#SEC_Contents">Contents</A>]</TD>
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<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdbint_abt.html#SEC_About"> ? </A>]</TD>
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</TR></TABLE>
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<H2> 2.2 The Target Side </H2>
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<!--docid::SEC4::-->
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<P>
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The target side of GDB is the "bits and bytes manipulator".
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Although it may make reference to symbolic info here and there, most
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of the target side will run with only a stripped executable
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available--or even no executable at all, in remote debugging cases.
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</P><P>
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Operations such as disassembly, stack frame crawls, and register
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display, are able to work with no symbolic info at all. In some cases,
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such as disassembly, GDB will use symbolic info to present addresses
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relative to symbols rather than as raw numbers, but it will work either
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way.
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</P><P>
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<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdbint_toc.html#SEC_Contents">Contents</A>]</TD>
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<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdbint_19.html#SEC186">Index</A>]</TD>
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<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdbint_abt.html#SEC_About"> ? </A>]</TD>
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</TR></TABLE>
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<H2> 2.3 Configurations </H2>
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<!--docid::SEC5::-->
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<P>
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<A NAME="IDX1"></A>
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<A NAME="IDX2"></A>
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<EM>Host</EM> refers to attributes of the system where GDB runs.
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<EM>Target</EM> refers to the system where the program being debugged
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executes. In most cases they are the same machine, in which case a
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third type of <EM>Native</EM> attributes come into play.
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</P><P>
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Defines and include files needed to build on the host are host support.
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Examples are tty support, system defined types, host byte order, host
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float format.
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</P><P>
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Defines and information needed to handle the target format are target
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dependent. Examples are the stack frame format, instruction set,
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breakpoint instruction, registers, and how to set up and tear down the stack
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to call a function.
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</P><P>
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Information that is only needed when the host and target are the same,
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is native dependent. One example is Unix child process support; if the
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host and target are not the same, doing a fork to start the target
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process is a bad idea. The various macros needed for finding the
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registers in the <CODE>upage</CODE>, running <CODE>ptrace</CODE>, and such are all
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in the native-dependent files.
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</P><P>
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Another example of native-dependent code is support for features that
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are really part of the target environment, but which require
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<CODE>#include</CODE> files that are only available on the host system. Core
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file handling and <CODE>setjmp</CODE> handling are two common cases.
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</P><P>
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When you want to make GDB work "native" on a particular machine, you
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have to include all three kinds of information.
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</P><P>
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<A NAME="Algorithms"></A>
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</P><P>
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<HR SIZE="6">
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<TABLE CELLPADDING=1 CELLSPACING=1 BORDER=0>
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<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdbint_toc.html#SEC_Contents">Contents</A>]</TD>
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<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdbint_19.html#SEC186">Index</A>]</TD>
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<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdbint_abt.html#SEC_About"> ? </A>]</TD>
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</TR></TABLE>
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<BR>
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<FONT SIZE="-1">
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<address>
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<p>Please send FSF & GNU inquiries & questions to <a
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href="mailto:gnu@gnu.org">gnu@gnu.org</a>. There are also <a
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href="http://www.gnu.org/home.html#ContactInfo">other ways to
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contact</a> the FSF.</p>
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<p>These pages are maintained by <a
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href="http://www.gnu.org/software/gdb/">the GDB developers</a>.</p>
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<p>Copyright Free Software Foundation, Inc., 59 Temple Place - Suite
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330, Boston, MA 02111, USA.</p>
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<p>Verbatim copying and distribution of this entire article is
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permitted in any medium, provided this notice is preserved.</p>
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</address>
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This document was generated
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by <I>GDB Administrator</I> on <I>October, 18 2002</I>
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using <A HREF="http://www.mathematik.uni-kl.de/~obachman/Texi2html
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