Subject: Re: [PATCH v2 3/3] Makefile: run coccicheck on more source files

From: SZEDER Gábor <[email-masked]>
Date: Fri, 13 Sep 2019 20:00:14 +0200

On Fri, Sep 13, 2019 at 10:14:01AM -0700, Denton Liu wrote:
> On Fri, Sep 13, 2019 at 01:49:52PM +0200, SZEDER Gábor wrote:
> > On Thu, Sep 12, 2019 at 11:40:36AM -0700, Junio C Hamano wrote:
> > > Denton Liu <[email-masked]> writes:
> > > 
> > > > +FIND_C_SOURCES = $(filter %.c,$(shell $(FIND_SOURCE_FILES)))
> > > > +COCCI_SOURCES = $(filter-out $(THIRD_PARTY_SOURCES),$(FIND_C_SOURCES))
> > > 
> > > The former is somewhat misnamed.  FIND_SOURCE_FILES is *not* a list
> > > of source files---it is a procedure to list source files to its
> > > standard output.  FIND_C_SOUCRES sounds as if it is a similar
> > > procedure, which would be implemented much like
> > > 
> > > 	FIND_C_SOURCES = $(FIND_SOURCE_FILES) | sed -n -e '/\.c$/p'
> > > 
> > > but that is not what you did and that is not what you want to have.
> > > Perhaps call it FOUND_C_SOURCES?
> > > 
> > > I wonder if we can get rid of FIND_SOURCE_FILES that is a mere
> > > procedure and replace its use with a true list of source files.
> > > Would it make the result more pleasant to work with?
> > > 
> > > Perhaps something like the attached patch, (which would come before
> > > this entire thing as a clean-up, and removing the need for 2/3)?
> > > 
> > > I dunno.
> > > 
> > > Using a procedure whose output is fed to xargs has an advantage that
> > > a platform with very short command line limit can still work with
> > > many source files, but the way you create and use COCCI_SOURCES in
> > > this patch would defeat that advantage anyway,
> > 
> > COCCI_SOURCES is only used as an input to 'xargs', so that advantage
> > is not defeated.
> 
> I think it still does matter; the relevant snippet is as follows:
> 
> 	if ! echo $(COCCI_SOURCES) | xargs $$limit \
> 		$(SPATCH) --sp-file $< $(SPATCH_FLAGS) \
> 		>$@+ 2>$@.log; \
> 
> which means that a really big COCCI_SOURCES could exceed the limit.

Oh, you're both right.

> That being said, COCCI_SOURCES should be smaller than the future
> SOURCE_FILES variable since we're only taking %.c files (and filtering
> out some of them too!).

We could also argue that Coccinelle only runs on platforms that have a
reasonably large command line arg limit, and the number of our source
files is way below that, so it won't matter in the foreseeable future.

(Furthermore, 'echo' is often a shell builtin command, and I don't
think that the platform's argument size limit applies to them.  At
least the 'echo' of dash, Bash, ksh, ksh93, mksh, and BusyBox sh can
deal with at least 10 million arguments; the platform limit is
somewhere around 147k)

> > > diff --git a/Makefile b/Makefile
> > > index f9255344ae..9dddd0e88c 100644
> > > --- a/Makefile
> > > +++ b/Makefile
> > > @@ -2584,7 +2584,7 @@ perl/build/man/man3/Git.3pm: perl/Git.pm
> > >  	$(QUIET_GEN)mkdir -p $(dir $@) && \
> > >  	pod2man $< $@
> > >  
> > > -FIND_SOURCE_FILES = ( \
> > > +SOURCE_FILES = $(patsubst ./%,%,$(shell \
> > >  	git ls-files \
> > >  		'*.[hcS]' \
> > >  		'*.sh' \
> > > @@ -2599,19 +2599,19 @@ FIND_SOURCE_FILES = ( \
> > >  		-o \( -name 'trash*' -type d -prune \) \
> > >  		-o \( -name '*.[hcS]' -type f -print \) \
> > >  		-o \( -name '*.sh' -type f -print \) \
> > > -	)
> > > +	))
> > >  
> > >  $(ETAGS_TARGET): FORCE
> > >  	$(RM) $(ETAGS_TARGET)
> > > -	$(FIND_SOURCE_FILES) | xargs etags -a -o $(ETAGS_TARGET)
> > > +	etags -a -o $(ETAGS_TARGET) $(SOURCE_FILES)
> > >  
> > >  tags: FORCE
> > >  	$(RM) tags
> > > -	$(FIND_SOURCE_FILES) | xargs ctags -a
> > > +	ctags -a $(SOURCE_FILES)
> > >  
> > >  cscope:
> > >  	$(RM) cscope*
> > > -	$(FIND_SOURCE_FILES) | xargs cscope -b
> > > +	cscope -b $(SOURCE_FILES)

Here, however, the list of source files is passed as argument to
non-builtin commands, that also might be used on
cmdline-arg-limit-challenged platforms.