User`s guide

Chapter 7: Debugging Machine Language Code

Tracing Execution at the Machine Level

The tracei command allows you to observe the progress of your program

while debugging machine code, just as you can with the trace command

while debugging source code. Thetracei command traces in units of machine

instructions instead of in lines of code.

Each trace is assigned a number when you create it. Use this number to

reference the breakpoint in the various commands provided for

manipulating breakpoints (for example, disable, enable, and delete, all

described in “Managing Breakpoints, Traces, and Conditional Commands”

on page 70).

The syntax of the tracei command is:

tracei [expression|variable]

Whenever the speciﬁed variable changes, dbx prints the old

and new values of that variable. (For machine-level

debugging.) Note that execution is very slow if you choose

this type of trace.

If the expression is of type pointer, look at the data pointed

to and watch until it changes. If the expression is not of type

pointer, look at the 32 bits at that address (assume the

expression evaluates to an address).

tracei procedure

This command is equivalent to entering trace procedure.

dbx prints the values of the parameters passed to the

speciﬁed procedure whenever your program calls it. Upon

return, dbx prints the return value.

tracei [expression|variable] at address

Prints the value of the variable whenever your program

reaches the speciﬁed address. (For machine-level

debugging.)

If the expression is of type pointer, look at the data pointed

to and watch until it changes. If the expression is not of type

pointer, look at the 32 bits at that address (assume the

expression evaluates to an address).