[Bashdb-devel] first GNU make with a debugger

[R. B. <ro...@pa...>]

I've patched GNU make 3.80 to add better tracing, error reporting and
I have added a debugger. It is in
http://bashdb.sourceforge.net/remake-3.80+dbg.tar.gz

What I have here is very very preliminary; it there so one can get a
feel for what a debugger for GNU Make might look like. I've only been
able to compile this on GNU/Linux with RedHat 9.0 or
Debian. Compilations on other OS's seem to give problems in places
that as far as I can tell are not related to any of the changes I've
made. For the debugger, you should have GNU readline installed.

Okay, now some sample output. Here's a small test Makefile: 

1: FOO=bar
2: all: foo
3: foo:
4: 	@echo hi > /dev/null
5: 	@fdafds

To get trace output, I've added the -x (or --trace) option. So:

  ./make -x -f bug2
produces: 

bug2:2 all
bug2:3 foo
bug2:4 foo
       echo hi > /dev/null
bug2:5 foo
       fdafds
make: fdafds: Command not found
bug2:3: *** [foo] Error 127

One small thing to note above is that when -x is in effect the @'s to
turn off echoing are disregarded. So you see the "echo hi" and "fdafds"
in the output.

If you want a target backtrace on errors, add -E. For the above, this
adds to the end:

#0  foo at bug2:3
#1  all at bug2:2

I've also tried this the actual Makefile to the modified make. At
present it still gives too much output, but boy is it much more
comprehensible compared to what you get with "make -d"

Okay, now on to the debugger! Just add -X (or --debugger) and you are
put into the debugger. Although I have a small command set right now
with few command formats or opitons, many of the most useful debugging
commands are there. You can set/delete breakpoints at a target, step
execution, restart or quit execution, turn on/off/toggle tracing, go
up or down the target backtrack stack and look at variables, Actually,
there are two kinds of print commands: "print" give a variable
source/file location and the value in symbolic terms.

For example when I run "p MAKE" inside the debugger (remake), I get: 

  (remake) p MAKE
  (null):0 MAKE = $(MAKE_COMMAND)

The (null):0 means this is a builtin definition. However there is
another print which does full expansion of the variables. So if I run
x (examine) instead I get: 

  (null):0 MAKE = /src/local-cvs/remake/src/./make

In fact, "examine" doesn't need a variable name, it will work with a
string. So I could type "x This is $(MAKE)" or 
"x $(bin_PROGRAMS) $(noinst_PROGRAMS)". For the latter, I get

make loadavg

Note, no location identification is given here (since what I put in
isn't a variable).

For those of you like myself who live inside of GNU Emacs, included in
the tarball is remake.el which uses on gud.el to provide running the
debugger inside GNU Emacs just as the way you'd do with perl, gdb, my
bash debugger. I also have a patched gud.el which contains the remake
debugger support. For front-end support such as this, I added "up" and
"down" debugger commands to postion you up or down in the Makefile
source.

Okay that's about it for now. I thought it would take a year or so to
get something I'm happy with. I'm a little ahead of schedule (but not
by much). I've been very pleased and surprised at how little work it
took for the gains I've gotten so far. It's a real pity no one has
undertaken this before, it hasn't been that hard.

Some interesting issues down the line will be in adding a command to
show dependency results or figuring out the right level of display on
a trace. Maybe there would be several levels: one doesn't want to step
through every file dependency of which most of them are
satisfied. Right now I use the hueristic unless a breakpoint is set I
stop at targets that are explicitly mentioned on the left-hand
side. This is probably still too much. "phony targets" and targets
with commands may be too little.