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Message-ID: <4A9CCC56.9090008@gmail.com>
Date: Tue, 01 Sep 2009 07:11:00 -0000
From: Dave Korn <dave.korn.cygwin@googlemail.com>
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To: Jie Zhang <jie.zhang@analog.com>
CC: Ralf.Wildenhues@gmx.de, binutils@sourceware.org
Subject: Re: Parallel build error for Blackfin target
References: <4A9CC410.7060301@analog.com>
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Jie Zhang wrote:

> Previously
> 
> bfin-lex.o: bfin-lex.c bfin-parse.h $(srcdir)/config/bfin-defs.h
>         $(COMPILE) -c $< $(NO_WERROR)
> 
> Now
> 
> bfin-lex.o: bfin-lex.c
> if am__fastdepCC
>         $(COMPILE) -MT $@ -MD -MP -MF $(DEPDIR)/$*.Tpo -c -o $@
> bfin-lex.c $(NO_WERROR)
>         mv -f $(DEPDIR)/$*.Tpo $(DEPDIR)/$*.Po
> else
> if AMDEP
>         source='bfin-lex.c' object='$@' libtool=no @AMDEPBACKSLASH@
>         DEPDIR=$(DEPDIR) $(CCDEPMODE) $(depcomp) @AMDEPBACKSLASH@
> endif
>         $(COMPILE) -c bfin-lex.c $(NO_WERROR)
> endif
> 
> Should I add back "bfin-parse.h $(srcdir)/config/bfin-defs.h" as the
> dependency of bfin-lex.o?

  Perhaps $(srcdir)/config/bfin-defs.h should be added as a preqrequisite of
bfin-parse.c (and hence implicitly of bfin-parse.h).

  Really the whole thing needs some kind of sentinel or stamp wrapped around
it(*); what we've got here is the typical "make doesn't understand when a
single rule updates more than one target at once" situation.  Running the rule
for bfin-parse.c actually also creates bfin-parse.h, which is what
necessitates the not-really-true-actually dependency of bfin-parse.h on
bfin-parse.c and the corresponding "@true" build rule.  See also Paul D.
Smith's Rules of Makefiles; this violates #2.

    cheers,
      DaveK

-- 
(*) - or perhaps to be converted to a multiple-output pattern rule, the other
way to resolve this kind of situation and the one place where make does
understand it might generate multiple outputs from a single rule.