[U-Boot-Users] [PATCH] Fix/workaround broken dependency handling with make 3.81

[Robert Schwebel]

On Mon, Aug 28, 2006 at 11:15:32PM +0200, Wolfgang Denk wrote:
> Yes, and IMHO you can easily show more problems with make. To me it's
> really frightening to see so many issues with a tool in so  wide  use
> like GNU make.

Well, make is powerful, so expect it to be complex :-)

> -> cat Makefile 
> all: hello_world.tgt
> 
> %.tgt: %
>         cp $< $@
> 
> %: %.src
>         cp $< $@
> 
> %.src: FORCE
>         touch $@
> 
> .PHONY: FORCE
> FORCE:
> -> make -n
> touch Makefile.src
> cp Makefile.src Makefile
> rm Makefile.src
> make: *** No targets.  Stop.
> -> ls -l
> total 0
> -rw-r--r--  1 wd users 0 Aug 28 23:08 Makefile
> -rw-r--r--  1 wd users 0 Aug 28 23:08 Makefile.src
> -> make --version
> GNU Make 3.80
> ...
> 
> So yes, your Makefile is dangerous.
> 
> But wait. I used "-n" on the command line. And the man page says:
> 
> 	-n   Print the commands that would be executed, but do not
>              execute them.
> 
> Do not execute them? So who did execute the "touch" and the "cp", but
> skip the "rm"? I'm frightened.

I don't have a solution, but some remarks:

from 'info make':

----------8<----------

	3.7 How Makefiles Are Remade
	============================

	[...]

	   To this end, after reading in all makefiles, `make' will consider
	each as a goal target and attempt to update it.  If a makefile has a
	rule which says how to update it (found either in that very makefile or
	in another one) or if an implicit rule applies to it (*note Using
	Implicit Rules: Implicit Rules.), it will be updated if necessary.

	[...]

	   When you use the `-t' or `--touch' option (*note Instead of Executing
	the Commands: Instead of Execution.), you would not want to use an
	out-of-date makefile to decide which targets to touch.  So the `-t'
	option has no effect on updating makefiles; they are really updated even
	if `-t' is specified.  Likewise, `-q' (or `--question') and `-n' (or
	`--just-print') do not prevent updating of makefiles, because an
	out-of-date makefile would result in the wrong output for other targets.

----------8<----------

So -n is being ignored for Makefile-remaking, and the "%: %.src" rule
is found as a goal target to update the Makefile from Makefile.src,
which is not there and thus being touched by using the "%.src: FORCE"
rule. 

> Actually: where is the "rm" coming from?

The file you refer to with "%" is an intermediate file, as it is part of
a chain. So it is being deleted automatically. If you don't want to do
that, declare it .INTERMEDIATE.

Here's a modified version which doens't work as well, but does if you
'make hello_world.src' manually (not the intended behaviour, but it
shows some things):

----------8<----------
all: hello_world.tgt

%.tgt: %
	cp $< $@

% :: %.src
	cp $< $@

%.src: FORCE
	touch $@

.INTERMEDIATE: hello_world

.PHONY: FORCE
FORCE:
----------8<----------

Note that I've declared % to be terminal, so Makefile is not rebuilt,
because there is no Makefile.src. 

rsc at isonoe:~/wd$ ll
total 4
-rw-r--r-- 1 rsc ptx 138 Aug 29 01:52 Makefile
-rw-r--r-- 1 rsc ptx   0 Aug 29 01:56 hello_world.src
rsc at isonoe:~/wd$ make
cp hello_world.src hello_world
cp hello_world hello_world.tgt
rsc at isonoe:~/wd$ ls -l 
total 4
-rw-r--r-- 1 rsc ptx 138 Aug 29 01:52 Makefile
-rw-r--r-- 1 rsc ptx   0 Aug 29 01:56 hello_world
-rw-r--r-- 1 rsc ptx   0 Aug 29 01:56 hello_world.src
-rw-r--r-- 1 rsc ptx   0 Aug 29 01:56 hello_world.tgt

Anyway, can't you avoid the match-anything rule somehow?

Robert
-- 
 Dipl.-Ing. Robert Schwebel | http://www.pengutronix.de
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