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Inter-Office Memorandum
fo Mesa Users Date October 17, 1977
From Barbara Koalkin Location Palo Alto
Subject Mesa 3.0 Debugger Update Organization SOD/SO
XEROX
Filed on: [MAXC]
This release of the Mesa debugger introduces many changes of interest and importance to all
Mesa programmers. Much work has been done to integrate the notion of configurations into
the debugger and make this new information available to the user. The purpose of this
memo is to make you aware of the changes that have taken place. More complete
explanations may be found in the file
Configurations: new commands and changes to existing commands
The major impact of the new configuration scheme on the debugger is to allow the user to
more closely specify the scope of the debugger's symbol search, thus saving on lookup time.
The notion of the current context has been expanded to include the current configuration in
addition to the current module and its corresponding frame within that configuration. The
current context is used for determining where the debugger is to begin its symbol lookup.
This applies for displaying variables as well as setting breakpoints, calling procedures, etc.
Upon entering the debugger for the first time, the current configuration is the last
configuration that was loaded and the current module is set to be its control module (if it
exists) or else the first module of the configuration.
Note that in all cases an instance name is required when a configuration or module name is
not unique.
CUrrent context
lists the name of the current module and its corresponding global frame address (and
instance name if one exists) followed by the name of the current configuration.
List Configurations
begins with the last configuration loaded and lists the names (and instance names, if they
exist) of al1 configurations that are loaded.
Display Configuration
lists the name of the current configuration followed by the names and the corresponding
global frame addresses (and instance names) of al1 the modules in the current configuration.
Mesa 3.0 Debu!~ger Update 2
SEt Root configuration configname
sets the current configuratio1l to be con/igllame, where con/igname is at the outermost level
of its configuration. This command will be sufficient for simple configurations of only one
level. It is also useful in getting you to the outermost level of nested configurations from
which you may move "in" using the following command.
SEt Configuration configname
sets the current configuration to be configname, where configname is nested within the root
configuration that is current. This command is useful for "jumping" further into the nested
block structure of a configuration.
SEt Module context modulename
sets the current context to be modulename (which must be contained in the current
configuration). Note that SEt Octal Context will continue to function as before and will
update the configuration/module context as well as changing the current frame.
Reset context
restores the context which this instance of the debugger had upon entering for the first time.
Display Variable var
searches for the value of var but now limits the scope of its search to the current context.
The lookup stops at the end of the call stack, whereas it previously continued its search by
following the binding path (which no longer exists). It continues to look aside to global
frames as well, but the search is limited only to the current context.
Find Variable var
looks through the whole current configuration, not only the current context, to find the
value and module location of var.
Display GlobalFrameTable
displays each module name and its corresponding octal frame address, pc, codebase, and gfi.
String Utility Commands
Interpret STring stringname startindex n
begins with startindex and lists n (decimal) characters from stringname.
Ascii read address n
displays n (decimal) characters starting at address.
Note that null characters are ignored by the display software, and therefore do not appear.
Control characters print as their corresponding alphanumeric preceeded by t.
Mesa 3.0 Debugger Update 3
Changes to Existing Commands
The Bind command has been taken out of the debugger completely, thus allowing the key
letters for Break Entry and Break Xit to be simplified. The New command and the STart
command will remain as before with the exception that New will no longer rlln any code.
Extended Capabilities
Esc buffers
The debugger tries to cut down on the amount of information that must be typed-in by
saving default values that may be used or inspected by typing ESC. The following additional
parameters are now being saved: configname, stringname, stringindex, and ascii read
address.
More breakpoints - breakpoint indicator <>
It is now possible to set breakpoints on statement boundaries instead of just text line
boundaries. The ind icalor <> will appear to the left of the source where the breakpoint is
set, ie. IF faa THEN <>some statement; .
Small things you will notice
There have been improvements in the display of small records (and small fields of records)
and the display of catch frames. In coordination with the language feature introducing
PACKED ARRAYS, the debugger will print them as well. You will also notice stronger version
checking when examining definitions modules.
If you use the optional window manager that is supplied with the system, you will notice
that the current window no longer changes when the mouse is repositioned. To bring a
window "on top" and make it current, position the mouse over it and click one of the mouse
buttons. This makes it a bit more difficult to find "lost" windows, but there is less chance
of a window disappearing accidently.
Documentation
The debugger documentation is now separate from the system document and can be found
on debugger and how to use the window manager found in Section 5.