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diff --git a/gdb/doc/gdb.alter-m4 b/gdb/doc/gdb.alter-m4 index 56007dd..e69de29 100755 --- a/gdb/doc/gdb.alter-m4 +++ b/gdb/doc/gdb.alter-m4 @@ -1,205 +0,0 @@ -_dnl__ Copyright (c) 1988 1989 1990 1991 Free Software Foundation, Inc. -_dnl__ This file is part of the source for the GDB manual. -@c M4 FRAGMENT: $Id$ -@node Altering, _GDBN__ Files, Symbols, Top -@chapter Altering Execution - -Once you think you have found an error in the program, you might want to -find out for certain whether correcting the apparent error would lead to -correct results in the rest of the run. You can find the answer by -experiment, using the _GDBN__ features for altering execution of the -program. - -For example, you can store new values into variables or memory -locations, give the program a signal, restart it at a different address, -or even return prematurely from a function to its caller. - -@menu -* Assignment:: Assignment to Variables -* Jumping:: Continuing at a Different Address -* Signaling:: Giving the Program a Signal -* Returning:: Returning from a Function -* Calling:: Calling your Program's Functions -@end menu - -@node Assignment, Jumping, Altering, Altering -@section Assignment to Variables - -@cindex assignment -@cindex setting variables -To alter the value of a variable, evaluate an assignment expression. -@xref{Expressions}. For example, - -@example -print x=4 -@end example - -@noindent -would store the value 4 into the variable @code{x}, and then print the -value of the assignment expression (which is 4). All the assignment -operators of C are supported, including the increment operators -@samp{++} and @samp{--}, and combining assignments such as @samp{+=} and -_0__@samp{<<=}_1__. - -@kindex set -@kindex set variable -@cindex variables, setting -If you are not interested in seeing the value of the assignment, use the -@code{set} command instead of the @code{print} command. @code{set} is -really the same as @code{print} except that the expression's value is not -printed and is not put in the value history (@pxref{Value History}). The -expression is evaluated only for its effects. - -If the beginning of the argument string of the @code{set} command -appears identical to a @code{set} subcommand, use the @code{set -variable} command instead of just @code{set}. This command is identical -to @code{set} except for its lack of subcommands. For example, a -program might well have a variable @code{width}---which leads to -an error if we try to set a new value with just @samp{set width=13}, as -we might if @code{set width} didn't happen to be a _GDBN__ command: -@example -(_GDBP__) whatis width -type = double -(_GDBP__) p width -$4 = 13 -(_GDBP__) set width=47 -Invalid syntax in expression. -@end example -@noindent -The invalid expression, of course, is @samp{=47}. What we can do in -order to actually set our program's variable @code{width} is -@example -(_GDBP__) set var width=47 -@end example - -_GDBN__ allows more implicit conversions in assignments than C does; you can -freely store an integer value into a pointer variable or vice versa, and -any structure can be converted to any other structure that is the same -length or shorter. -@comment FIXME: how do structs align/pad in these conversions? -@comment /pesch@cygnus.com 18dec1990 - -To store values into arbitrary places in memory, use the @samp{@{@dots{}@}} -construct to generate a value of specified type at a specified address -(@pxref{Expressions}). For example, @code{@{int@}0x83040} refers -to memory location @code{0x83040} as an integer (which implies a certain size -and representation in memory), and - -@example -set @{int@}0x83040 = 4 -@end example - -@noindent -stores the value 4 into that memory location. - -@node Jumping, Signaling, Assignment, Altering -@section Continuing at a Different Address - -Ordinarily, when you continue the program, you do so at the place where -it stopped, with the @code{continue} command. You can instead continue at -an address of your own choosing, with the following commands: - -@table @code -@item jump @var{linespec} -@kindex jump -Resume execution at line @var{linespec}. Execution will stop -immediately if there is a breakpoint there. @xref{List} for a -description of the different forms of @var{linespec}. - -The @code{jump} command does not change the current stack frame, or -the stack pointer, or the contents of any memory location or any -register other than the program counter. If line @var{linespec} is in -a different function from the one currently executing, the results may -be bizarre if the two functions expect different patterns of arguments or -of local variables. For this reason, the @code{jump} command requests -confirmation if the specified line is not in the function currently -executing. However, even bizarre results are predictable if you are -well acquainted with the machine-language code of the program. - -@item jump *@var{address} -Resume execution at the instruction at address @var{address}. -@end table - -You can get much the same effect as the @code{jump} command by storing a -new value into the register @code{$pc}. The difference is that this -does not start the program running; it only changes the address where it -@emph{will} run when it is continued. For example, - -@example -set $pc = 0x485 -@end example - -@noindent -causes the next @code{continue} command or stepping command to execute at -address 0x485, rather than at the address where the program stopped. -@xref{Stepping}. - -The most common occasion to use the @code{jump} command is to back up, -perhaps with more breakpoints set, over a portion of a program that has -already executed, in order to examine its execution in more detail. - -@node Signaling, Returning, Jumping, Altering -@c @group -@section Giving the Program a Signal - -@table @code -@item signal @var{signalnum} -@kindex signal -Resume execution where the program stopped, but give it immediately the -signal number @var{signalnum}. - -Alternatively, if @var{signalnum} is zero, continue execution without -giving a signal. This is useful when the program stopped on account of -a signal and would ordinary see the signal when resumed with the -@code{continue} command; @samp{signal 0} causes it to resume without a -signal. - -@code{signal} does not repeat when you press @key{RET} a second time -after executing the command. -@end table -@c @end group - -@node Returning, Calling, Signaling, Altering -@section Returning from a Function - -@table @code -@item return -@itemx return @var{expression} -@cindex returning from a function -@kindex return -You can cancel execution of a function call with the @code{return} -command. If you give an -@var{expression} argument, its value is used as the function's return -value. -@end table - -When you use @code{return}, _GDBN__ discards the selected stack frame -(and all frames within it). You can think of this as making the -discarded frame return prematurely. If you wish to specify a value to -be returned, give that value as the argument to @code{return}. - -This pops the selected stack frame (@pxref{Selection}), and any other -frames inside of it, leaving its caller as the innermost remaining -frame. That frame becomes selected. The specified value is stored in -the registers used for returning values of functions. - -The @code{return} command does not resume execution; it leaves the -program stopped in the state that would exist if the function had just -returned. In contrast, the @code{finish} command (@pxref{Stepping}) -resumes execution until the selected stack frame returns naturally. - -@node Calling, , Returning, Altering -@section Calling your Program's Functions - -@cindex calling functions -@kindex call -@table @code -@item call @var{expr} -Evaluate the expression @var{expr} without displaying @code{void} -returned values. -@end table - -You can use this variant of the @code{print} command if you want to -execute a function from your program, but without cluttering the output -with @code{void} returned values. The result is printed and saved in -the value history, if it is not void. |