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Re: breakpoint for accessing memory location


Eli Zaretskii wrote:

I fixed the manual as shown below. Please see if this addresses your concerns.


It certainly does. See one nit below.


Thanks,

Erik Leunissen

 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 one or more variables
^^^^^^^^^^^^^

We watch for a change in the value of the variable, OK. However the corresponding expression for that case simply holds the *name* of the variable, doesn't it?

+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 @@
@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
                                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
                                      same here

+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 @@
@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 @@
@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





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