9.2 Specifying a Location
Several gdb commands accept arguments that specify a location
of your program's code. Since gdb is a source-level
debugger, a location usually specifies some line in the source code;
for that reason, locations are also known as linespecs.
Here are all the different ways of specifying a code location that
- Specifies the line number linenum of the current source file.
- Specifies the line offset lines before or after the current
line. For the
list command, the current line is the last one
printed; for the breakpoint commands, this is the line at which
execution stopped in the currently selected stack frame
(see Frames, for a description of stack frames.) When
used as the second of the two linespecs in a
this specifies the line offset lines up or down from the first
- Specifies the line linenum in the source file filename.
If filename is a relative file name, then it will match any
source file name with the same trailing components. For example, if
filename is `gcc/expr.c', then it will match source file
name of /build/trunk/gcc/expr.c, but not
/build/trunk/libcpp/expr.c or /build/trunk/gcc/x-expr.c.
- Specifies the line that begins the body of the function function.
For example, in C, this is the line with the open brace.
- Specifies the line where label appears in function.
- Specifies the line that begins the body of the function function
in the file filename. You only need the file name with a
function name to avoid ambiguity when there are identically named
functions in different source files.
- Specifies the line at which the label named label appears.
gdb searches for the label in the function corresponding to
the currently selected stack frame. If there is no current selected
stack frame (for instance, if the inferior is not running), then
gdb will not search for a label.
- Specifies the program address address. For line-oriented
commands, such as
edit, this specifies a source
line that contains address. For
break and other
breakpoint oriented commands, this can be used to set breakpoints in
parts of your program which do not have debugging information or
Here address may be any expression valid in the current working
language (see working language) that specifies a code
address. In addition, as a convenience, gdb extends the
semantics of expressions used in locations to cover the situations
that frequently happen during debugging. Here are the various forms
- Any expression valid in the current working language.
- An address of a function or procedure derived from its name. In C,
C++, Java, Objective-C, Fortran, minimal, and assembly, this is
simply the function's name function (and actually a special case
of a valid expression). In Pascal and Modula-2, this is
&function. In Ada, this is function
(although the Pascal form also works).
This form specifies the address of the function's first instruction,
before the stack frame and arguments have been set up.
- Like funcaddr above, but also specifies the name of the source
file explicitly. This is useful if the name of the function does not
specify the function unambiguously, e.g., if there are several
functions with identical names in different source files.