linux-kernel - Re: [PATCH] perf tools: Fix build error on read only source.

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Message-ID: <20100818171917.GH9410@ghostprotocols.net>
Date:	Wed, 18 Aug 2010 14:19:18 -0300
From:	Arnaldo Carvalho de Melo <acme@...radead.org>
To:	Bernd Petrovitsch <bernd@...prog.at>
Cc:	Kusanagi Kouichi <slash@...auone-net.jp>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Mackerras <paulus@...ba.org>, Ingo Molnar <mingo@...e.hu>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf tools: Fix build error on read only source.

Em Wed, Aug 18, 2010 at 05:25:41PM +0200, Bernd Petrovitsch escreveu:
> On Mit, 2010-08-18 at 11:14 -0300, Arnaldo Carvalho de Melo wrote:
> > But with this we're back using $(shell mkdir), Bernd, ideas on how to
> > properly fix this, probably the feature tests have to be triggered by
> > the first rule and probably be something like:
> > 
> > $(phony feature-tests): 
> First, this should probably have been:
> .PHONY: feature-tests

Humm, isn't $(phony feature-tests): variation valid and shorter, humm,
yeah, seems to be for !GNU make :-\

(http://makepp.sourceforge.net/1.18/t_phony.html)

> > -include feature-tests.mak
> > 
> > DIRECTORY_DEPS = $(LIB_OBJS) $(BUILTIN_OBJS) $(OUTPUT)PERF-VERSION-FILE $(OUTPUT)common-cmds.h
> > $(DIRECTORY_DEPS): $(sort $(dir $(DIRECTORY_DEPS))) feature-tests
> >
> > completely untested! Unsure if this would trigger the mkdir first tho.
> >
> > Right?
> 
> This doesn't trigger it. I played around a little bit and didn't find
> any way to trigger any rule.
> The "problem" is IMHO that "try-cc" is used in "ifeq" clauses and these
> are evaluated as `make` goes through the Makefile before the first
> (real) rule (like "all") is triggered.
> 
> So ATM I see only 3 possibilities:
> 1) The old (aka ugly) "solution" from above.
> 2) Add to try-cc something like
> 	[ -d "$(OUTPUT)" ] || mkdir -p "$(OUTPUT)" 2>/dev/null;
> before the line with the "echo".
> The '[ -d "$(OUTPUT)" ]' is not really necessary as `mkdir -p` is a
> no-op on existing directories.

Probably 2) is the best, since we'll end up creating that dir anyway.
But as PeterZ pointed out, this is all moot since the kernel behaviour
for O= is to expect the directory specified to already exist.

We're left with the task of checking that and providing a meaningful
answer if not, like this:

[acme@...lia linux-2.6-tip]$ ls -la ~/git/build/foo
ls: cannot access /home/acme/git/build/foo: No such file or directory
[acme@...lia linux-2.6-tip]$ make O=~/git/build/foo
/bin/sh: line 0: cd: /home/acme/git/build/foo: No such file or directory
Makefile:117: *** output directory "/home/acme/git/build/foo" does not exist.  Stop.
[acme@...lia linux-2.6-tip]$

> 3) Another possibility would be to move the temporary file into the /tmp
> directory as into
> ----  snip  ----
> try-cc = $(shell sh -c						  \
> 	'TMP="/tmp/$(TMPOUT).$$$$";		 		  \
> 	 echo "$(1)" |						  \
> 	 $(CC) -x c - $(2) -o "$$TMP" > /dev/null 2>&1 && echo y; \
> 	 rm -f "$$TMP"')
> ----  snip  ----
> If yes, we could use (and thus depend on) `mktemp` - which is usual
> shell script way to generate unique temporary filename - as in

There is no use of mktemp in Kbuild, that I try hard to use as reference
here.

- Arnaldo
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