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* gdb.texinfo (Breakpoints, Set Watchpoints): Elaborate and

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clarify on the possible meanings of ``expression'' watched by
	watchpoints.  Add indexing.
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Eli Zaretskii 2006-10-21 12:50:16 +00:00
parent 286ba84deb
commit fd60e0dfdf
2 changed files with 46 additions and 8 deletions
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@ -1,3 +1,9 @@
2006-10-21 Eli Zaretskii <eliz@gnu.org>
* gdb.texinfo (Breakpoints, Set Watchpoints): Elaborate and
clarify on the possible meanings of ``expression'' watched by
watchpoints. Add indexing.
2006-10-17 Daniel Jacobowitz <dan@codesourcery.com>
* gdbint.texinfo (Target Vector Definition): Move most

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gdb/doc/gdb.texinfo
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@ -2773,15 +2773,19 @@ in shared library routines that are not called directly by the program
call).
@cindex watchpoints
@cindex data breakpoints
@cindex memory tracing
@cindex breakpoint on memory address
@cindex breakpoint on variable modification
A @dfn{watchpoint} is a special breakpoint that stops your program
when the value of an expression changes. You must use a different
command to set watchpoints (@pxref{Set Watchpoints, ,Setting
watchpoints}), but aside from that, you can manage a watchpoint like
any other breakpoint: you enable, disable, and delete both breakpoints
and watchpoints using the same commands.
when the value of an expression changes. The expression may be a value
of a variable, or it could involve values of on or more variables
combined by operators, such as @samp{a + b}. This is sometimes called
@dfn{data breakpoints}. You must use a different command to set
watchpoints (@pxref{Set Watchpoints, ,Setting watchpoints}), but aside
from that, you can manage a watchpoint like any other breakpoint: you
enable, disable, and delete both breakpoints and watchpoints using the
same commands.
You can arrange to have values from your program displayed automatically
whenever @value{GDBN} stops at a breakpoint. @xref{Auto Display,,
@ -3106,7 +3110,24 @@ You can see these breakpoints with the @value{GDBN} maintenance command
@cindex setting watchpoints
You can use a watchpoint to stop execution whenever the value of an
expression changes, without having to predict a particular place where
this may happen.
this may happen. (This is sometimes called a @dfn{data breakpoint}.)
The expression may be as simple as the value of a single variable, or
as complex as many variables combined by operators. Examples include:
@itemize @bullet
@item
A reference to the value of a single variable.
@item
An address cast to an appropriate data type. For example,
@samp{*(int *)0x12345678} will watch a 4-byte region at the specified
address (assuming an @code{int} occupies 4 bytes).
@item
An arbitrarily complex expression, such as @samp{a*b + c/d}. The
expression can use any operators valid in the program's native
language (@pxref{Languages}).
@end itemize
@cindex software watchpoints
@cindex hardware watchpoints
@ -3124,8 +3145,14 @@ watchpoints, which do not slow down the running of your program.
@table @code
@kindex watch
@item watch @var{expr}
Set a watchpoint for an expression. @value{GDBN} will break when @var{expr}
is written into by the program and its value changes.
Set a watchpoint for an expression. @value{GDBN} will break when the
expression @var{expr} is written into by the program and its value
changes. The simplest (and the most popular) use of this command is
to watch the value of a single variable:
@smallexample
(@value{GDBP}) watch foo
@end smallexample
@kindex rwatch
@item rwatch @var{expr}
@ -3217,6 +3244,11 @@ Hardware watchpoint @var{num}: Could not insert watchpoint
@noindent
If this happens, delete or disable some of the watchpoints.
Watching complex expressions that reference many variables can also
exhaust the resources available for hardware-assisted watchpoints.
That's because @value{GDBN} needs to watch every variable in the
expression with separately allocated resources.
The SPARClite DSU will generate traps when a program accesses some data
or instruction address that is assigned to the debug registers. For the
data addresses, DSU facilitates the @code{watch} command. However the