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Path: utzoo!linus!decvax!wivax!cadmus!harvard!seismo!mcvax!enea!kim
From: kim@enea.UUCP (Kim Walden)
Newsgroups: net.unix,net.unix-wizards
Subject: Re: Make vs. source control
Message-ID: <771@enea.UUCP>
Date: Fri, 2-Nov-84 07:27:10 EST
Article-I.D.: enea.771
Posted: Fri Nov  2 07:27:10 1984
Date-Received: Sun, 4-Nov-84 04:40:13 EST
References: <2490@dartvax.UUCP> <765@ariel.UUCP> <61@pixutl.UUCP> <cyb-eng.425>
Reply-To: kim@enea.UUCP ( Walden)
Organization: ENEA DATA, Sweden
Lines: 56
Xref: mcvax net.unix:680 net.unix-wizards:6506Summary: 

In article <cyb-eng.425> howard@cyb-eng.UUCP (Howard Johnson) writes:
>[munch]
>>	The problem of overwriting source files if the SCCS parent file
>>	was modified can be helped a great deal by changing the $(GET) lines
>>	in rules.c from:
>>
>>	"\t$(GET) $(GFLAGS) -p $< > $*.c",
>>
>>	to:
>>
>>	"\t$(GET) $(GFLAGS) $<",
>>
>>	and let 'get' check if the file is writable. I have done this and
>>	prefer it to the original.
>
>The only problem with this suggestion is that $*.c is not necessarily in the
>current directory, and 'get' places it's g-file in the current directory.
>I'll admit that the first construct is dangerous, but there may be a better
>fix for the problem:
>
>	"\ttest -w $*.c || $(GET) $(GFLAGS) -p $< > $*.c",


The standard System V built-in make rules for getting files from SCCS
are certainly erroneous, but none of the replacements suggested
so far are adequate. 
The command line above does not work for two reasons:

	1. When $*.c already exists and is read-only, the > will fail.

	2. When the $(GET) succeeds it leaves $*.c writable, which
	   is not what we want. A subsequent "get -e" then fails with
	   "writable 'file' exists".

By the way, it is very dangerous to checkout changes to built-in make
rules in superuser mode, because write permission is then silently
granted even when all write bits are off.

The following rule type seems to solve the problems:
(the leading '-' prevents a premature make exit):

".c~.c:",
"\t-test -w $@ || { rm -f $@ ; $(GET) $(GFLAGS) -p $< > $@ ; chmod 444 $@ ; }"


Note that in multi-step rules, where g-files are obtained, processed,
and removed, a simple get is sufficient, e.g.:

".c~:",
"\t$(GET) $(GFLAGS) -p $< > $*.c",
"\t$(CC) $(CFLAGS) $*.c $(LDFLAGS) -n -o $@",
"\t-rm -f $*.c"

			Kim Walden
			ENEA DATA, Sweden
			...decvax!mcvax!enea!kim