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diff --git a/gdb/doc/gdb.sample-m4 b/gdb/doc/gdb.sample-m4 index ae258ad..e69de29 100755 --- a/gdb/doc/gdb.sample-m4 +++ b/gdb/doc/gdb.sample-m4 @@ -1,263 +0,0 @@ -_dnl__ -*- Texinfo -*- -_dnl__ Copyright (c) 1991 Free Software Foundation, Inc. -_dnl__ This file is part of the source for the GDB manual. -@c M4 FRAGMENT: $Id$ -@node Sample Session, Invocation, New Features, Top -@chapter A Sample _GDBN__ Session - -You can use this manual at your leisure to read all about _GDBN__. -However, a handful of commands are enough to get started using the -debugger. This chapter illustrates these commands. - -@iftex -In this sample session, we emphasize user input like this: @i{input}, -to make it easier to pick out from the surrounding output. -@end iftex - -@c FIXME: this example may not be appropriate for some configs, where -@c FIXME...primary interest is in remote use. -_0__ -One of the preliminary versions of GNU @code{m4} (a generic macro -processor) exhibits the following bug: sometimes, when we change its -quote strings from the default, the commands used to capture one macro's -definition in another stop working. In the following short @code{m4} -session, we define a macro @code{foo} which expands to @code{0000}; we -then use the @code{m4} builtin @code{defn} to define @code{bar} as the -same thing. However, when we change the open quote string to -@code{<QUOTE>} and the close quote string to @code{<UNQUOTE>}, the same -procedure fails to define a new synonym @code{baz}: - -@smallexample -$ @i{cd gnu/m4} -$ @i{./m4} -@i{define(foo,0000)} - -@i{foo} -0000 -@i{define(bar,defn(`foo'))} - -@i{bar} -0000 -@i{changequote(<QUOTE>,<UNQUOTE>)} - -@i{define(baz,defn(<QUOTE>foo<UNQUOTE>))} -@i{baz} -@i{C-D} -m4: End of input: 0: fatal error: EOF in string -@end smallexample - -@noindent -Let's use _GDBN__ to try to see what's going on. - -@smallexample -$ @i{_GDBP__ m4} -Reading symbol data from m4...done. -(_GDBP__) -@end smallexample - -@noindent -_GDBN__ only reads enough symbol data to know where to find the rest -when needed; as a result, the first prompt comes up very quickly. We -then tell _GDBN__ to use a narrower display width than usual, so -that examples will fit in this manual. - -@smallexample -(_GDBP__) @i{set width 70} -@end smallexample - -@noindent -Let's see how the @code{m4} builtin @code{changequote} works. -Having looked at the source, we know the relevant subroutine is -@code{m4_changequote}, so we set a breakpoint there with _GDBN__'s -@code{break} command. - -@smallexample -(_GDBP__) @i{break m4_changequote} -Breakpoint 1 at 0x62f4: file builtin.c, line 879. -@end smallexample - -@noindent -Using the @code{run} command, we start @code{m4} running under _GDBN__ -control; as long as control does not reach the @code{m4_changequote} -subroutine, the program runs as usual: - -@smallexample -(_GDBP__) @i{run} -Starting program: /work/Editorial/gdb/gnu/m4/m4 -@i{define(foo,0000)} - -@i{foo} -0000 -@end smallexample - -@noindent -To trigger the breakpoint, we call @code{changequote}. _GDBN__ -suspends execution of @code{m4}, displaying information about the -context where it stops. - -@smallexample -@i{changequote(<QUOTE>,<UNQUOTE>)} - -Breakpoint 1, m4_changequote (argc=3, argv=0x33c70) at builtin.c:879 -879 if (bad_argc(TOKEN_DATA_TEXT(argv[0]), argc, 1, 3)) -@end smallexample - -@noindent -Now we use the command @code{n} (@code{next}) to advance execution to -the next line of the current function. - -@smallexample -(_GDBP__) @i{n} -882 set_quotes((argc >= 2) ? TOKEN_DATA_TEXT(argv[1]) : nil, -@end smallexample - -@noindent -@code{set_quotes} looks like a promising subroutine. We can go into it -by using the command @code{s} (@code{step}) instead of @code{next}. -@code{step} goes to the next line to be executed in @emph{any} -subroutine, so it steps into @code{set_quotes}. - -@smallexample -(_GDBP__) @i{s} -set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>") - at input.c:530 -530 if (lquote != def_lquote) -@end smallexample - -@noindent -The summary display showing the subroutine where @code{m4} is now -suspended (and its arguments) is called a stack frame display. We can -use the @code{backtrace} command (which can also be spelled @code{bt}), -to see where we are in the stack: it displays a stack frame for each -active subroutine. - -@smallexample -(_GDBP__) @i{bt} -#0 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>") - at input.c:530 -#1 0x6344 in m4_changequote (argc=3, argv=0x33c70) at builtin.c:882 -#2 0x8174 in expand_macro (sym=0x33320) at macro.c:242 -#3 0x7a88 in expand_token (obs=0x0, t=209696, td=0xf7fffa30) - at macro.c:71 -#4 0x79dc in expand_input () at macro.c:40 -#5 0x2930 in main (argc=0, argv=0xf7fffb20) at m4.c:195 -@end smallexample - -@noindent -Let's step through a few more lines to see what happens. The first two -times, we can use @samp{s}; the next two times we use @code{n} to avoid -falling into the @code{xstrdup} subroutine. -@smallexample -(_GDBP__) @i{s} -0x3b5c 532 if (rquote != def_rquote) -(_GDBP__) @i{s} -0x3b80 535 lquote = (lq == nil || *lq == '\0') ? def_lquote :\ - xstrdup(lq); -(_GDBP__) @i{n} -536 rquote = (rq == nil || *rq == '\0') ? def_rquote : xstrdup\ -(rq); -(_GDBP__) @i{n} -538 len_lquote = strlen(rquote); -@end smallexample - -@noindent -The last line displayed looks a little odd; let's examine the variables -@code{lquote} and @code{rquote} to see if they are in fact the new left -and right quotes we specified. We can use the command @code{p} -(@code{print}) to see their values. - -@smallexample -(_GDBP__) @i{p lquote} -$1 = 0x35d40 "<QUOTE>" -(_GDBP__) @i{p rquote} -$2 = 0x35d50 "<UNQUOTE>" -@end smallexample - -@noindent -@code{lquote} and @code{rquote} are indeed the new left and right quotes. -Let's look at some context; we can display ten lines of source -surrounding the current line, with the @code{l} (@code{list}) command. - -@smallexample -(_GDBP__) @i{l} -533 xfree(rquote); -534 -535 lquote = (lq == nil || *lq == '\0') ? def_lquote : xstrdup\ -(lq); -536 rquote = (rq == nil || *rq == '\0') ? def_rquote : xstrdup\ -(rq); -537 -538 len_lquote = strlen(rquote); -539 len_rquote = strlen(lquote); -540 @} -541 -542 void -@end smallexample - -@noindent -Let's step past the two lines that set @code{len_lquote} and -@code{len_rquote}, and then examine the values of those variables. - -@smallexample -(_GDBP__) @i{n} -539 len_rquote = strlen(lquote); -(_GDBP__) @i{n} -540 @} -(_GDBP__) @i{p len_lquote} -$3 = 9 -(_GDBP__) @i{p len_rquote} -$4 = 7 -@end smallexample - -@noindent -That certainly looks wrong, assuming @code{len_lquote} and -@code{len_rquote} are meant to be the lengths of @code{lquote} and -@code{rquote} respectively. Let's try setting them to better values. -We can use the @code{p} command for this, since it'll print the value of -any expression---and that expression can include subroutine calls and -assignments. - -@smallexample -(_GDBP__) p len_lquote=strlen(lquote) -$5 = 7 -(_GDBP__) p len_rquote=strlen(rquote) -$6 = 9 -@end smallexample - -@noindent -Let's see if that fixes the problem of using the new quotes with the -@code{m4} built-in @code{defn}. We can allow @code{m4} to continue -executing with the @code{c} (@code{continue}) command, and then try the -example that caused trouble initially: - -@smallexample -(_GDBP__) @i{c} -Continuing. - -@i{define(baz,defn(<QUOTE>foo<UNQUOTE>))} - -baz -0000 -@end smallexample - -@noindent -Success! The new quotes now work just as well as the default ones. The -problem seems to have been just the two typos defining the wrong -lengths. We'll let @code{m4} exit by giving it an EOF as input. - -@smallexample -@i{C-D} -Program exited normally. -@end smallexample - -@noindent -The message @samp{Program exited normally.} is from _GDBN__; it -indicates @code{m4} has finished executing. We can end our _GDBN__ -session with the _GDBN__ @code{quit} command. - -@smallexample -(_GDBP__) @i{quit} - -$ -_1__@end smallexample - |