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610 lines
25 KiB
HTML
15 years ago
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<HTML>
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<!-- Created on March, 27 2008 by texi2html 1.64 -->
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<!--
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Written by: Lionel Cons <Lionel.Cons@cern.ch> (original author)
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Karl Berry <karl@freefriends.org>
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Olaf Bachmann <obachman@mathematik.uni-kl.de>
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and many others.
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Maintained by: Olaf Bachmann <obachman@mathematik.uni-kl.de>
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Send bugs and suggestions to <texi2html@mathematik.uni-kl.de>
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-->
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<HEAD>
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<TITLE>Debugging with GDB: Stack</TITLE>
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<META NAME="description" CONTENT="Debugging with GDB: Stack">
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<META NAME="keywords" CONTENT="Debugging with GDB: Stack">
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<META NAME="resource-type" CONTENT="document">
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<META NAME="distribution" CONTENT="global">
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<META NAME="Generator" CONTENT="texi2html 1.64">
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</HEAD>
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<BODY LANG="" BGCOLOR="#FFFFFF" TEXT="#000000" LINK="#0000FF" VLINK="#800080" ALINK="#FF0000">
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<A NAME="SEC46"></A>
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<TABLE CELLPADDING=1 CELLSPACING=1 BORDER=0>
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<TR><TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_6.html#SEC45"> < </A>]</TD>
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<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_7.html#SEC47"> > </A>]</TD>
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<TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_8.html#SEC51"> << </A>]</TD>
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<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb.html#SEC_Top"> Up </A>]</TD>
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<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_8.html#SEC51"> >> </A>]</TD>
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<TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb.html#SEC_Top">Top</A>]</TD>
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<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_toc.html#SEC_Contents">Contents</A>]</TD>
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<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_38.html#SEC764">Index</A>]</TD>
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<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_abt.html#SEC_About"> ? </A>]</TD>
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</TR></TABLE>
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<H1> 6. Examining the Stack </H1>
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<!--docid::SEC46::-->
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<P>
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When your program has stopped, the first thing you need to know is where it
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stopped and how it got there.
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</P><P>
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<A NAME="IDX283"></A>
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Each time your program performs a function call, information about the call
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is generated.
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That information includes the location of the call in your program,
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the arguments of the call,
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and the local variables of the function being called.
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The information is saved in a block of data called a <EM>stack frame</EM>.
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The stack frames are allocated in a region of memory called the <EM>call
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stack</EM>.
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</P><P>
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When your program stops, the GDB commands for examining the
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stack allow you to see all of this information.
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</P><P>
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<A NAME="IDX284"></A>
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One of the stack frames is <EM>selected</EM> by GDB and many
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GDB commands refer implicitly to the selected frame. In
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particular, whenever you ask GDB for the value of a variable in
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your program, the value is found in the selected frame. There are
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special GDB commands to select whichever frame you are
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interested in. See section <A HREF="gdb_7.html#SEC49">Selecting a Frame</A>.
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</P><P>
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When your program stops, GDB automatically selects the
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currently executing frame and describes it briefly, similar to the
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<CODE>frame</CODE> command (see section <A HREF="gdb_7.html#SEC50">Information about a Frame</A>).
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</P><P>
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<BLOCKQUOTE><TABLE BORDER=0 CELLSPACING=0>
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<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="gdb_7.html#SEC47">6.1 Stack Frames</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP">Stack frames</TD></TR>
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<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="gdb_7.html#SEC48">6.2 Backtraces</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP"></TD></TR>
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<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="gdb_7.html#SEC49">6.3 Selecting a Frame</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP">Selecting a frame</TD></TR>
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<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="gdb_7.html#SEC50">6.4 Information About a Frame</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP">Information on a frame</TD></TR>
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</TABLE>
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<br>
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</BLOCKQUOTE>
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<P>
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<A NAME="Frames"></A>
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<HR SIZE="6">
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<A NAME="SEC47"></A>
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<TABLE CELLPADDING=1 CELLSPACING=1 BORDER=0>
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<TR><TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_7.html#SEC46"> < </A>]</TD>
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<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_7.html#SEC48"> > </A>]</TD>
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<TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_7.html#SEC46"> << </A>]</TD>
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<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_7.html#SEC46"> Up </A>]</TD>
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<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_8.html#SEC51"> >> </A>]</TD>
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<TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb.html#SEC_Top">Top</A>]</TD>
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<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_toc.html#SEC_Contents">Contents</A>]</TD>
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<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_38.html#SEC764">Index</A>]</TD>
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<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_abt.html#SEC_About"> ? </A>]</TD>
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</TR></TABLE>
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<H2> 6.1 Stack Frames </H2>
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<!--docid::SEC47::-->
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<P>
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<A NAME="IDX285"></A>
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<A NAME="IDX286"></A>
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The call stack is divided up into contiguous pieces called <EM>stack
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frames</EM>, or <EM>frames</EM> for short; each frame is the data associated
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with one call to one function. The frame contains the arguments given
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to the function, the function's local variables, and the address at
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which the function is executing.
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</P><P>
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<A NAME="IDX287"></A>
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<A NAME="IDX288"></A>
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<A NAME="IDX289"></A>
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When your program is started, the stack has only one frame, that of the
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function <CODE>main</CODE>. This is called the <EM>initial</EM> frame or the
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<EM>outermost</EM> frame. Each time a function is called, a new frame is
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made. Each time a function returns, the frame for that function invocation
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is eliminated. If a function is recursive, there can be many frames for
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the same function. The frame for the function in which execution is
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actually occurring is called the <EM>innermost</EM> frame. This is the most
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recently created of all the stack frames that still exist.
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</P><P>
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<A NAME="IDX290"></A>
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Inside your program, stack frames are identified by their addresses. A
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stack frame consists of many bytes, each of which has its own address; each
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kind of computer has a convention for choosing one byte whose
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address serves as the address of the frame. Usually this address is kept
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in a register called the <EM>frame pointer register</EM>
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(see section <A HREF="gdb_9.html#SEC69">$fp</A>) while execution is going on in that frame.
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</P><P>
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<A NAME="IDX291"></A>
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GDB assigns numbers to all existing stack frames, starting with
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zero for the innermost frame, one for the frame that called it,
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and so on upward. These numbers do not really exist in your program;
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they are assigned by GDB to give you a way of designating stack
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frames in GDB commands.
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</P><P>
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<A NAME="IDX292"></A>
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Some compilers provide a way to compile functions so that they operate
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without stack frames. (For example, the GCC option
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<TABLE><tr><td> </td><td class=smallexample><FONT SIZE=-1><pre><SAMP>`-fomit-frame-pointer'</SAMP>
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</FONT></pre></td></tr></table>generates functions without a frame.)
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This is occasionally done with heavily used library functions to save
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the frame setup time. GDB has limited facilities for dealing
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with these function invocations. If the innermost function invocation
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has no stack frame, GDB nevertheless regards it as though
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it had a separate frame, which is numbered zero as usual, allowing
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correct tracing of the function call chain. However, GDB has
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no provision for frameless functions elsewhere in the stack.
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</P><P>
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<DL COMPACT>
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<A NAME="IDX293"></A>
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<A NAME="IDX294"></A>
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<DT><CODE>frame <VAR>args</VAR></CODE>
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<DD>The <CODE>frame</CODE> command allows you to move from one stack frame to another,
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and to print the stack frame you select. <VAR>args</VAR> may be either the
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address of the frame or the stack frame number. Without an argument,
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<CODE>frame</CODE> prints the current stack frame.
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<P>
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<A NAME="IDX295"></A>
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<A NAME="IDX296"></A>
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<DT><CODE>select-frame</CODE>
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<DD>The <CODE>select-frame</CODE> command allows you to move from one stack frame
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to another without printing the frame. This is the silent version of
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<CODE>frame</CODE>.
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</DL>
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<P>
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<A NAME="Backtrace"></A>
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<HR SIZE="6">
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<A NAME="SEC48"></A>
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<TABLE CELLPADDING=1 CELLSPACING=1 BORDER=0>
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<TR><TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_7.html#SEC47"> < </A>]</TD>
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<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_7.html#SEC49"> > </A>]</TD>
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<TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_7.html#SEC49"> << </A>]</TD>
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<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_7.html#SEC46"> Up </A>]</TD>
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<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_8.html#SEC51"> >> </A>]</TD>
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<TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb.html#SEC_Top">Top</A>]</TD>
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<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_toc.html#SEC_Contents">Contents</A>]</TD>
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<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_38.html#SEC764">Index</A>]</TD>
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<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_abt.html#SEC_About"> ? </A>]</TD>
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</TR></TABLE>
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<H2> 6.2 Backtraces </H2>
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<!--docid::SEC48::-->
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<P>
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<A NAME="IDX297"></A>
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<A NAME="IDX298"></A>
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A backtrace is a summary of how your program got where it is. It shows one
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line per frame, for many frames, starting with the currently executing
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frame (frame zero), followed by its caller (frame one), and on up the
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stack.
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</P><P>
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<DL COMPACT>
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<A NAME="IDX299"></A>
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<A NAME="IDX300"></A>
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<DT><CODE>backtrace</CODE>
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<DD><DT><CODE>bt</CODE>
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<DD>Print a backtrace of the entire stack: one line per frame for all
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frames in the stack.
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<P>
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You can stop the backtrace at any time by typing the system interrupt
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character, normally <KBD>Ctrl-c</KBD>.
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</P><P>
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<DT><CODE>backtrace <VAR>n</VAR></CODE>
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<DD><DT><CODE>bt <VAR>n</VAR></CODE>
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<DD>Similar, but print only the innermost <VAR>n</VAR> frames.
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<P>
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<DT><CODE>backtrace -<VAR>n</VAR></CODE>
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<DD><DT><CODE>bt -<VAR>n</VAR></CODE>
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<DD>Similar, but print only the outermost <VAR>n</VAR> frames.
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<P>
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<DT><CODE>backtrace full</CODE>
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<DD><DT><CODE>bt full</CODE>
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<DD><DT><CODE>bt full <VAR>n</VAR></CODE>
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<DD><DT><CODE>bt full -<VAR>n</VAR></CODE>
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<DD>Print the values of the local variables also. <VAR>n</VAR> specifies the
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number of frames to print, as described above.
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</DL>
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<P>
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<A NAME="IDX301"></A>
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<A NAME="IDX302"></A>
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The names <CODE>where</CODE> and <CODE>info stack</CODE> (abbreviated <CODE>info s</CODE>)
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are additional aliases for <CODE>backtrace</CODE>.
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</P><P>
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<A NAME="IDX303"></A>
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In a multi-threaded program, GDB by default shows the
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backtrace only for the current thread. To display the backtrace for
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several or all of the threads, use the command <CODE>thread apply</CODE>
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(see section <A HREF="gdb_5.html#SEC27">thread apply</A>). For example, if you type <KBD>thread
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apply all backtrace</KBD>, GDB will display the backtrace for all
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the threads; this is handy when you debug a core dump of a
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multi-threaded program.
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</P><P>
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Each line in the backtrace shows the frame number and the function name.
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The program counter value is also shown--unless you use <CODE>set
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print address off</CODE>. The backtrace also shows the source file name and
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line number, as well as the arguments to the function. The program
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counter value is omitted if it is at the beginning of the code for that
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line number.
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</P><P>
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Here is an example of a backtrace. It was made with the command
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<SAMP>`bt 3'</SAMP>, so it shows the innermost three frames.
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</P><P>
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<TABLE><tr><td> </td><td class=smallexample><FONT SIZE=-1><pre>#0 m4_traceon (obs=0x24eb0, argc=1, argv=0x2b8c8)
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at builtin.c:993
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#1 0x6e38 in expand_macro (sym=0x2b600) at macro.c:242
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#2 0x6840 in expand_token (obs=0x0, t=177664, td=0xf7fffb08)
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at macro.c:71
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(More stack frames follow...)
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</FONT></pre></td></tr></table></P><P>
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The display for frame zero does not begin with a program counter
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value, indicating that your program has stopped at the beginning of the
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code for line <CODE>993</CODE> of <CODE>builtin.c</CODE>.
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</P><P>
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<A NAME="IDX304"></A>
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<A NAME="IDX305"></A>
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If your program was compiled with optimizations, some compilers will
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optimize away arguments passed to functions if those arguments are
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never used after the call. Such optimizations generate code that
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passes arguments through registers, but doesn't store those arguments
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in the stack frame. GDB has no way of displaying such
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arguments in stack frames other than the innermost one. Here's what
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such a backtrace might look like:
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</P><P>
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|
|
<TABLE><tr><td> </td><td class=smallexample><FONT SIZE=-1><pre>#0 m4_traceon (obs=0x24eb0, argc=1, argv=0x2b8c8)
|
||
|
|
at builtin.c:993
|
||
|
|
#1 0x6e38 in expand_macro (sym=<value optimized out>) at macro.c:242
|
||
|
|
#2 0x6840 in expand_token (obs=0x0, t=<value optimized out>, td=0xf7fffb08)
|
||
|
|
at macro.c:71
|
||
|
|
(More stack frames follow...)
|
||
|
|
</FONT></pre></td></tr></table></P><P>
|
||
|
|
|
||
|
|
The values of arguments that were not saved in their stack frames are
|
||
|
|
shown as <SAMP>`<value optimized out>'</SAMP>.
|
||
|
|
</P><P>
|
||
|
|
|
||
|
|
If you need to display the values of such optimized-out arguments,
|
||
|
|
either deduce that from other variables whose values depend on the one
|
||
|
|
you are interested in, or recompile without optimizations.
|
||
|
|
</P><P>
|
||
|
|
|
||
|
|
<A NAME="IDX306"></A>
|
||
|
|
<A NAME="IDX307"></A>
|
||
|
|
<A NAME="IDX308"></A>
|
||
|
|
Most programs have a standard user entry point--a place where system
|
||
|
|
libraries and startup code transition into user code. For C this is
|
||
|
|
<CODE>main</CODE><A NAME="DOCF3" HREF="gdb_fot.html#FOOT3">(3)</A>.
|
||
|
|
When GDB finds the entry function in a backtrace
|
||
|
|
it will terminate the backtrace, to avoid tracing into highly
|
||
|
|
system-specific (and generally uninteresting) code.
|
||
|
|
</P><P>
|
||
|
|
|
||
|
|
If you need to examine the startup code, or limit the number of levels
|
||
|
|
in a backtrace, you can change this behavior:
|
||
|
|
</P><P>
|
||
|
|
|
||
|
|
<DL COMPACT>
|
||
|
|
<DT><CODE>set backtrace past-main</CODE>
|
||
|
|
<DD><DT><CODE>set backtrace past-main on</CODE>
|
||
|
|
<DD><A NAME="IDX309"></A>
|
||
|
|
Backtraces will continue past the user entry point.
|
||
|
|
<P>
|
||
|
|
|
||
|
|
<DT><CODE>set backtrace past-main off</CODE>
|
||
|
|
<DD>Backtraces will stop when they encounter the user entry point. This is the
|
||
|
|
default.
|
||
|
|
<P>
|
||
|
|
|
||
|
|
<DT><CODE>show backtrace past-main</CODE>
|
||
|
|
<DD><A NAME="IDX310"></A>
|
||
|
|
Display the current user entry point backtrace policy.
|
||
|
|
<P>
|
||
|
|
|
||
|
|
<DT><CODE>set backtrace past-entry</CODE>
|
||
|
|
<DD><DT><CODE>set backtrace past-entry on</CODE>
|
||
|
|
<DD>Backtraces will continue past the internal entry point of an application.
|
||
|
|
This entry point is encoded by the linker when the application is built,
|
||
|
|
and is likely before the user entry point <CODE>main</CODE> (or equivalent) is called.
|
||
|
|
<P>
|
||
|
|
|
||
|
|
<DT><CODE>set backtrace past-entry off</CODE>
|
||
|
|
<DD>Backtraces will stop when they encounter the internal entry point of an
|
||
|
|
application. This is the default.
|
||
|
|
<P>
|
||
|
|
|
||
|
|
<DT><CODE>show backtrace past-entry</CODE>
|
||
|
|
<DD>Display the current internal entry point backtrace policy.
|
||
|
|
<P>
|
||
|
|
|
||
|
|
<DT><CODE>set backtrace limit <VAR>n</VAR></CODE>
|
||
|
|
<DD><DT><CODE>set backtrace limit 0</CODE>
|
||
|
|
<DD><A NAME="IDX311"></A>
|
||
|
|
Limit the backtrace to <VAR>n</VAR> levels. A value of zero means
|
||
|
|
unlimited.
|
||
|
|
<P>
|
||
|
|
|
||
|
|
<DT><CODE>show backtrace limit</CODE>
|
||
|
|
<DD>Display the current limit on backtrace levels.
|
||
|
|
</DL>
|
||
|
|
<P>
|
||
|
|
|
||
|
|
<A NAME="Selection"></A>
|
||
|
|
<HR SIZE="6">
|
||
|
|
<A NAME="SEC49"></A>
|
||
|
|
<TABLE CELLPADDING=1 CELLSPACING=1 BORDER=0>
|
||
|
|
<TR><TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_7.html#SEC48"> < </A>]</TD>
|
||
|
|
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_7.html#SEC50"> > </A>]</TD>
|
||
|
|
<TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_7.html#SEC50"> << </A>]</TD>
|
||
|
|
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_7.html#SEC46"> Up </A>]</TD>
|
||
|
|
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_8.html#SEC51"> >> </A>]</TD>
|
||
|
|
<TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb.html#SEC_Top">Top</A>]</TD>
|
||
|
|
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_toc.html#SEC_Contents">Contents</A>]</TD>
|
||
|
|
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_38.html#SEC764">Index</A>]</TD>
|
||
|
|
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_abt.html#SEC_About"> ? </A>]</TD>
|
||
|
|
</TR></TABLE>
|
||
|
|
<H2> 6.3 Selecting a Frame </H2>
|
||
|
|
<!--docid::SEC49::-->
|
||
|
|
<P>
|
||
|
|
|
||
|
|
Most commands for examining the stack and other data in your program work on
|
||
|
|
whichever stack frame is selected at the moment. Here are the commands for
|
||
|
|
selecting a stack frame; all of them finish by printing a brief description
|
||
|
|
of the stack frame just selected.
|
||
|
|
</P><P>
|
||
|
|
|
||
|
|
<DL COMPACT>
|
||
|
|
<A NAME="IDX312"></A>
|
||
|
|
<A NAME="IDX313"></A>
|
||
|
|
<DT><CODE>frame <VAR>n</VAR></CODE>
|
||
|
|
<DD><DT><CODE>f <VAR>n</VAR></CODE>
|
||
|
|
<DD>Select frame number <VAR>n</VAR>. Recall that frame zero is the innermost
|
||
|
|
(currently executing) frame, frame one is the frame that called the
|
||
|
|
innermost one, and so on. The highest-numbered frame is the one for
|
||
|
|
<CODE>main</CODE>.
|
||
|
|
<P>
|
||
|
|
|
||
|
|
<DT><CODE>frame <VAR>addr</VAR></CODE>
|
||
|
|
<DD><DT><CODE>f <VAR>addr</VAR></CODE>
|
||
|
|
<DD>Select the frame at address <VAR>addr</VAR>. This is useful mainly if the
|
||
|
|
chaining of stack frames has been damaged by a bug, making it
|
||
|
|
impossible for GDB to assign numbers properly to all frames. In
|
||
|
|
addition, this can be useful when your program has multiple stacks and
|
||
|
|
switches between them.
|
||
|
|
<P>
|
||
|
|
|
||
|
|
On the SPARC architecture, <CODE>frame</CODE> needs two addresses to
|
||
|
|
select an arbitrary frame: a frame pointer and a stack pointer.
|
||
|
|
</P><P>
|
||
|
|
|
||
|
|
On the MIPS and Alpha architecture, it needs two addresses: a stack
|
||
|
|
pointer and a program counter.
|
||
|
|
</P><P>
|
||
|
|
|
||
|
|
On the 29k architecture, it needs three addresses: a register stack
|
||
|
|
pointer, a program counter, and a memory stack pointer.
|
||
|
|
</P><P>
|
||
|
|
|
||
|
|
<A NAME="IDX314"></A>
|
||
|
|
<DT><CODE>up <VAR>n</VAR></CODE>
|
||
|
|
<DD>Move <VAR>n</VAR> frames up the stack. For positive numbers <VAR>n</VAR>, this
|
||
|
|
advances toward the outermost frame, to higher frame numbers, to frames
|
||
|
|
that have existed longer. <VAR>n</VAR> defaults to one.
|
||
|
|
<P>
|
||
|
|
|
||
|
|
<A NAME="IDX315"></A>
|
||
|
|
<A NAME="IDX316"></A>
|
||
|
|
<DT><CODE>down <VAR>n</VAR></CODE>
|
||
|
|
<DD>Move <VAR>n</VAR> frames down the stack. For positive numbers <VAR>n</VAR>, this
|
||
|
|
advances toward the innermost frame, to lower frame numbers, to frames
|
||
|
|
that were created more recently. <VAR>n</VAR> defaults to one. You may
|
||
|
|
abbreviate <CODE>down</CODE> as <CODE>do</CODE>.
|
||
|
|
</DL>
|
||
|
|
<P>
|
||
|
|
|
||
|
|
All of these commands end by printing two lines of output describing the
|
||
|
|
frame. The first line shows the frame number, the function name, the
|
||
|
|
arguments, and the source file and line number of execution in that
|
||
|
|
frame. The second line shows the text of that source line.
|
||
|
|
</P><P>
|
||
|
|
|
||
|
|
For example:
|
||
|
|
</P><P>
|
||
|
|
|
||
|
|
<TABLE><tr><td> </td><td class=smallexample><FONT SIZE=-1><pre>(gdb) up
|
||
|
|
#1 0x22f0 in main (argc=1, argv=0xf7fffbf4, env=0xf7fffbfc)
|
||
|
|
at env.c:10
|
||
|
|
10 read_input_file (argv[i]);
|
||
|
|
</FONT></pre></td></tr></table></P><P>
|
||
|
|
|
||
|
|
After such a printout, the <CODE>list</CODE> command with no arguments
|
||
|
|
prints ten lines centered on the point of execution in the frame.
|
||
|
|
You can also edit the program at the point of execution with your favorite
|
||
|
|
editing program by typing <CODE>edit</CODE>.
|
||
|
|
See section <A HREF="gdb_8.html#SEC52">Printing Source Lines</A>,
|
||
|
|
for details.
|
||
|
|
</P><P>
|
||
|
|
|
||
|
|
<DL COMPACT>
|
||
|
|
<A NAME="IDX317"></A>
|
||
|
|
<A NAME="IDX318"></A>
|
||
|
|
<DT><CODE>up-silently <VAR>n</VAR></CODE>
|
||
|
|
<DD><DT><CODE>down-silently <VAR>n</VAR></CODE>
|
||
|
|
<DD>These two commands are variants of <CODE>up</CODE> and <CODE>down</CODE>,
|
||
|
|
respectively; they differ in that they do their work silently, without
|
||
|
|
causing display of the new frame. They are intended primarily for use
|
||
|
|
in GDB command scripts, where the output might be unnecessary and
|
||
|
|
distracting.
|
||
|
|
</DL>
|
||
|
|
<P>
|
||
|
|
|
||
|
|
<A NAME="Frame Info"></A>
|
||
|
|
<HR SIZE="6">
|
||
|
|
<A NAME="SEC50"></A>
|
||
|
|
<TABLE CELLPADDING=1 CELLSPACING=1 BORDER=0>
|
||
|
|
<TR><TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_7.html#SEC49"> < </A>]</TD>
|
||
|
|
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_8.html#SEC51"> > </A>]</TD>
|
||
|
|
<TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_7.html#SEC46"> << </A>]</TD>
|
||
|
|
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_7.html#SEC46"> Up </A>]</TD>
|
||
|
|
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_8.html#SEC51"> >> </A>]</TD>
|
||
|
|
<TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb.html#SEC_Top">Top</A>]</TD>
|
||
|
|
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_toc.html#SEC_Contents">Contents</A>]</TD>
|
||
|
|
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_38.html#SEC764">Index</A>]</TD>
|
||
|
|
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_abt.html#SEC_About"> ? </A>]</TD>
|
||
|
|
</TR></TABLE>
|
||
|
|
<H2> 6.4 Information About a Frame </H2>
|
||
|
|
<!--docid::SEC50::-->
|
||
|
|
<P>
|
||
|
|
|
||
|
|
There are several other commands to print information about the selected
|
||
|
|
stack frame.
|
||
|
|
</P><P>
|
||
|
|
|
||
|
|
<DL COMPACT>
|
||
|
|
<DT><CODE>frame</CODE>
|
||
|
|
<DD><DT><CODE>f</CODE>
|
||
|
|
<DD>When used without any argument, this command does not change which
|
||
|
|
frame is selected, but prints a brief description of the currently
|
||
|
|
selected stack frame. It can be abbreviated <CODE>f</CODE>. With an
|
||
|
|
argument, this command is used to select a stack frame.
|
||
|
|
See section <A HREF="gdb_7.html#SEC49">Selecting a Frame</A>.
|
||
|
|
<P>
|
||
|
|
|
||
|
|
<A NAME="IDX319"></A>
|
||
|
|
<A NAME="IDX320"></A>
|
||
|
|
<DT><CODE>info frame</CODE>
|
||
|
|
<DD><DT><CODE>info f</CODE>
|
||
|
|
<DD>This command prints a verbose description of the selected stack frame,
|
||
|
|
including:
|
||
|
|
<P>
|
||
|
|
|
||
|
|
<UL>
|
||
|
|
<LI>
|
||
|
|
the address of the frame
|
||
|
|
<LI>
|
||
|
|
the address of the next frame down (called by this frame)
|
||
|
|
<LI>
|
||
|
|
the address of the next frame up (caller of this frame)
|
||
|
|
<LI>
|
||
|
|
the language in which the source code corresponding to this frame is written
|
||
|
|
<LI>
|
||
|
|
the address of the frame's arguments
|
||
|
|
<LI>
|
||
|
|
the address of the frame's local variables
|
||
|
|
<LI>
|
||
|
|
the program counter saved in it (the address of execution in the caller frame)
|
||
|
|
<LI>
|
||
|
|
which registers were saved in the frame
|
||
|
|
</UL>
|
||
|
|
<P>
|
||
|
|
|
||
|
|
The verbose description is useful when
|
||
|
|
something has gone wrong that has made the stack format fail to fit
|
||
|
|
the usual conventions.
|
||
|
|
</P><P>
|
||
|
|
|
||
|
|
<DT><CODE>info frame <VAR>addr</VAR></CODE>
|
||
|
|
<DD><DT><CODE>info f <VAR>addr</VAR></CODE>
|
||
|
|
<DD>Print a verbose description of the frame at address <VAR>addr</VAR>, without
|
||
|
|
selecting that frame. The selected frame remains unchanged by this
|
||
|
|
command. This requires the same kind of address (more than one for some
|
||
|
|
architectures) that you specify in the <CODE>frame</CODE> command.
|
||
|
|
See section <A HREF="gdb_7.html#SEC49">Selecting a Frame</A>.
|
||
|
|
<P>
|
||
|
|
|
||
|
|
<A NAME="IDX321"></A>
|
||
|
|
<DT><CODE>info args</CODE>
|
||
|
|
<DD>Print the arguments of the selected frame, each on a separate line.
|
||
|
|
<P>
|
||
|
|
|
||
|
|
<DT><CODE>info locals</CODE>
|
||
|
|
<DD><A NAME="IDX322"></A>
|
||
|
|
Print the local variables of the selected frame, each on a separate
|
||
|
|
line. These are all variables (declared either static or automatic)
|
||
|
|
accessible at the point of execution of the selected frame.
|
||
|
|
<P>
|
||
|
|
|
||
|
|
<A NAME="IDX323"></A>
|
||
|
|
<A NAME="IDX324"></A>
|
||
|
|
<A NAME="IDX325"></A>
|
||
|
|
<DT><CODE>info catch</CODE>
|
||
|
|
<DD>Print a list of all the exception handlers that are active in the
|
||
|
|
current stack frame at the current point of execution. To see other
|
||
|
|
exception handlers, visit the associated frame (using the <CODE>up</CODE>,
|
||
|
|
<CODE>down</CODE>, or <CODE>frame</CODE> commands); then type <CODE>info catch</CODE>.
|
||
|
|
See section <A HREF="gdb_6.html#SEC35">Setting Catchpoints</A>.
|
||
|
|
<P>
|
||
|
|
|
||
|
|
</DL>
|
||
|
|
<P>
|
||
|
|
|
||
|
|
<A NAME="Source"></A>
|
||
|
|
<HR SIZE="6">
|
||
|
|
<TABLE CELLPADDING=1 CELLSPACING=1 BORDER=0>
|
||
|
|
<TR><TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_7.html#SEC46"> << </A>]</TD>
|
||
|
|
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_8.html#SEC51"> >> </A>]</TD>
|
||
|
|
<TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb.html#SEC_Top">Top</A>]</TD>
|
||
|
|
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_toc.html#SEC_Contents">Contents</A>]</TD>
|
||
|
|
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_38.html#SEC764">Index</A>]</TD>
|
||
|
|
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_abt.html#SEC_About"> ? </A>]</TD>
|
||
|
|
</TR></TABLE>
|
||
|
|
<BR>
|
||
|
|
<FONT SIZE="-1">
|
||
|
|
|
||
|
|
<address>
|
||
|
|
|
||
|
|
<p>Please send FSF & GNU inquiries & questions to <a
|
||
|
|
href="mailto:gnu@gnu.org">gnu@gnu.org</a>. There are also <a
|
||
|
|
href="http://www.gnu.org/home.html#ContactInfo">other ways to
|
||
|
|
contact</a> the FSF.</p>
|
||
|
|
|
||
|
|
<p>These pages are maintained by <a
|
||
|
|
href="http://www.gnu.org/software/gdb/">the GDB developers</a>.</p>
|
||
|
|
|
||
|
|
<p>Copyright Free Software Foundation, Inc., 59 Temple Place - Suite
|
||
|
|
330, Boston, MA 02111, USA.</p>
|
||
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This document was generated
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