pdx - pascal debugger
pdx [-r] [objfile]
Pdx is a tool for source level debugging and execution of Pascal programs. The objfile is
an object file produced by the Pascal translator pi(1). If no objfile is specified, pdx
looks for a file named ``obj'' in the current directory. The object file contains a sym-
bol table which includes the name of the all the source files translated by pi to create
it. These files are available for perusal while using the debugger.
If the file ``.pdxinit'' exists in the current directory, then the debugger commands in it
The -r option causes the objfile to be executed immediately; if it terminates successfully
pdx exits. Otherwise it reports the reason for termination and offers the user the option
of entering the debugger or simply letting px continue with a traceback. If -r is not
specified, pdx just prompts and waits for a command.
The commands are:
run [args] [< filename] [> filename]
Start executing objfile, passing args as command line arguments; < or > can be used
to redirect input or output in the usual manner.
trace [in procedure/function] [if condition]
trace source-line-number [if condition]
trace procedure/function [in procedure/function] [if condition]
trace expression at source-line-number [if condition]
trace variable [in procedure/function] [if condition]
Have tracing information printed when the program is executed. A number is associ-
ated with the command that is used to turn the tracing off (see the delete com-
The first argument describes what is to be traced. If it is a source-line-number,
then the line is printed immediately prior to being executed. Source line numbers
in a file other than the current one must be preceded by the name of the file and a
colon, e.g. ``mumble.p:17''.
If the argument is a procedure or function name then every time it is called,
information is printed telling what routine called it, from what source line it was
called, and what parameters were passed to it. In addition, its return is noted,
and if it's a function then the value it is returning is also printed.
If the argument is an expression with an at clause then the value of the expression
is printed whenever the identified source line is reached.
If the argument is a variable then the name and value of the variable is printed
whenever it changes. Execution is substantially slower during this form of trac-
If no argument is specified then all source lines are printed before they are exe-
cuted. Execution is substantially slower during this form of tracing.
The clause ``in procedure/function'' restricts tracing information to be printed
only while executing inside the given procedure or function.
Condition is a Pascal boolean expression and is evaluated prior to printing the
tracing information; if it is false then the information is not printed.
There is no restriction on the amount of information that can be traced.
stop if condition
stop at source-line-number [if condition]
stop in procedure/function [if condition]
stop variable [if condition]
Stop execution when the given line is reached, procedure or function called, vari-
able changed, or condition true.
The trace or stop corresponding to the given number is removed. The numbers asso-
ciated with traces and stops are printed by the status command.
status [> filename]
Print out the currently active trace and stop commands.
cont Continue execution from where it stopped. This can only be done when the program
was stopped by an interrupt or through use of the stop command.
step Execute one source line.
next Execute up to the next source line. The difference between this and step is that
if the line contains a call to a procedure or function the step command will stop
at the beginning of that block, while the next command will not.
print expression [, expression ...]
Print out the values of the Pascal expressions. Variables declared in an outer
block but having the same identifier as one in the current block may be referenced
as ``block-name . variable''.
Print the declaration of the given identifier.
Print the full qualification of the given identifer, i.e. the outer blocks that
the identifier is associated with.
assign variable expression
Assign the value of the expression to the variable.
Execute the object code associated with the named procedure or function.
help Print out a synopsis of pdx commands.
gripe Invokes a mail program to send a message to the person in charge of pdx.
where Print out a list of the active procedures and functions and the respective source
line where they are called.
Read pdx commands from the given filename. Especially useful when the filename has
been created by redirecting a status command from an earlier debugging session.
dump [> filename]
Print the names and values of all active data.
list [source-line-number [, source-line-number]]
List the lines in the current source file from the first line number to the second
inclusive. As in the editor ``$'' can be used to refer to the last line. If no
lines are specified, the entire file is listed. If the name of a procedure or
function is given lines n-k to n+k are listed where n is the first statement in the
procedure or function and k is small.
Change the current source file name to filename. If none is specified then the
current source file name is printed.
Invoke an editor on filename or the current source file if none is specified. If a
procedure or function name is specified, the editor is invoked on the file that
contains it. Which editor is invoked by default depends on the installation. The
default can be overridden by setting the environment variable EDITOR to the name of
the desired editor.
pi Recompile the program and read in the new symbol table information.
Pass the command line to the shell for execution. The SHELL environment variable
determines which shell is used.
alias new-command-name old-command-name
This command makes pdx respond to new-command-name the way it used to respond to
quit Exit pdx.
The following commands deal with the program at the px instruction level rather than
source level. They are not intended for general use.
tracei [address] [if cond]
tracei [variable] [at address] [if cond]
stopi [address] [if cond]
stopi [at] [address] [if cond]
Turn on tracing or set a stop using a px machine instruction addresses.
xi address [, address]
Print the instructions starting at the first address. Instructions up to the sec-
ond address are printed.
xd address [, address]
Print in octal the specified data location(s).
obj Pascal object file
.pdxinit Pdx initialization file
An Introduction to Pdx
Pdx does not understand sets, and provides no information about files.
The whatis command doesn't quite work for variant records.
Bad things will happen if a procedure invoked with the call command does a non-local goto.
The commands step and next should be able to take a count that specifies how many lines to
There should be commands stepi and nexti that correspond to step and next but work at the
There should be a way to get an address associated with a line number, procedure or func-
tion, and variable.
Most of the command names are too long.
The alias facility is quite weak.
A csh-like history capability would improve the situation.
4.2 Berkeley Distribution April 29, 1985 PDX(1)