Breakpoints are set with the break
command (abbreviated
b
). The debugger convenience variable `$bpnum' records the
number of the breakpoint you've set most recently; see section Convenience variables, for a discussion of what you can do with
convenience variables.
You have several ways to say where the breakpoint should go.
break function
break +offset
break -offset
break linenum
break filename:linenum
break filename:function
break *address
break
break
sets a breakpoint at
the next instruction to be executed in the selected stack frame
(see section Examining the Stack). In any selected frame but the
innermost, this makes your program stop as soon as control
returns to that frame. This is similar to the effect of a
finish
command in the frame inside the selected frame--except
that finish
does not leave an active breakpoint. If you use
break
without an argument in the innermost frame, GDB stops
the next time it reaches the current location; this may be useful
inside loops.
GDB normally ignores breakpoints when it resumes execution, until at
least one instruction has been executed. If it did not do this, you
would be unable to proceed past a breakpoint without first disabling the
breakpoint. This rule applies whether or not the breakpoint already
existed when your program stopped.
break ... if cond
tbreak args
break
command, and the breakpoint is set in the same
way, but the breakpoint is automatically deleted after the first time your
program stops there. See section Disabling breakpoints.
hbreak args
break
command and the breakpoint is set in the same way, but the
breakpoint requires hardware support and some target hardware may not
have this support. The main purpose of this is EPROM/ROM code
debugging, so you can set a breakpoint at an instruction without
changing the instruction. This can be used with the new trap-generation
provided by SPARClite DSU and some x86-based targets. These targets
will generate traps when a program accesses some data or instruction
address that is assigned to the debug registers. However the hardware
breakpoint registers can take a limited number of breakpoints. For
example, on the DSU, only two data breakpoints can be set at a time, and
GDB will reject this command if more than two are used. Delete
or disable unused hardware breakpoints before setting new ones
(see section Disabling breakpoints). See section Break conditions.
thbreak args
hbreak
command and the breakpoint is set in
the same way. However, like the tbreak
command,
the breakpoint is automatically deleted after the
first time your program stops there. Also, like the hbreak
command, the breakpoint requires hardware support and some target hardware
may not have this support. See section Disabling breakpoints.
See also section Break conditions.
rbreak regex
break
command. You can delete them, disable them, or make
them conditional the same way as any other breakpoint.
The syntax of the regular expression is the standard one used with tools
like `grep'. Note that this is different from the syntax used by
shells, so for instance foo*
matches all functions that include
an fo
followed by zero or more o
s. There is an implicit
.*
leading and trailing the regular expression you supply, so to
match only functions that begin with foo
, use ^foo
.
When debugging C++ programs, rbreak
is useful for setting
breakpoints on overloaded functions that are not members of any special
classes.
info breakpoints [n]
info break [n]
info watchpoints [n]
info break
shows the condition on
the line following the affected breakpoint; breakpoint commands, if any,
are listed after that.
info break
with a breakpoint
number n as argument lists only that breakpoint. The
convenience variable $_
and the default examining-address for
the x
command are set to the address of the last breakpoint
listed (see section Examining memory).
info break
displays a count of the number of times the breakpoint
has been hit. This is especially useful in conjunction with the
ignore
command. You can ignore a large number of breakpoint
hits, look at the breakpoint info to see how many times the breakpoint
was hit, and then run again, ignoring one less than that number. This
will get you quickly to the last hit of that breakpoint.
GDB allows you to set any number of breakpoints at the same place in your program. There is nothing silly or meaningless about this. When the breakpoints are conditional, this is even useful (see section Break conditions).
GDB itself sometimes sets breakpoints in your program for special
purposes, such as proper handling of longjmp
(in C programs).
These internal breakpoints are assigned negative numbers, starting with
-1
; `info breakpoints' does not display them.
You can see these breakpoints with the GDB maintenance command `maint info breakpoints'.
maint info breakpoints
breakpoint
watchpoint
longjmp
longjmp
calls.
longjmp resume
longjmp
.
until
until
command.
finish
finish
command.
shlib events
Go to the first, previous, next, last section, table of contents.