linux-kernel - Re: [PATCH v4 5/8] kbuild: add fine grained build dependencies for exported symbols

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Date:	Thu, 3 Mar 2016 21:46:38 -0500 (EST)
From:	Nicolas Pitre <nicolas.pitre@...aro.org>
To:	Michal Marek <mmarek@...e.com>
cc:	linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 5/8] kbuild: add fine grained build dependencies for
 exported symbols

On Thu, 3 Mar 2016, Michal Marek wrote:

> Dne 29.2.2016 v 04:48 Nicolas Pitre napsal(a):
> > +# Filter out exported kernel symbol names advertised as warning pragmas
> > +# by the preprocessor and write them to $(1). We must consider continuation
> > +# lines as well: they start with a blank, or the preceeding line ends with
> > +# a ':'. Anything else is passed through as is.
> > +# See also __KSYM_DEP() in include/linux/export.h.
> > +ksym_dep_filter = sed -n \
> > +	-e '1 {x; $$!d}' \
> > +	-e '/^ / {H; $$!d}' \
> > +	-e 'x; /:$$/ {x; H; $$!d; s/^/ /; x}' \
> > +	-e ':filter; /^.*KBUILD_AUTOKSYM_DEP: /! {p; b next}' \
> > +	-e 's//KSYM_/; s/\n.*//; w $(1)' \
> > +	-e ':next; $$!d' \
> > +	-e '1 q; s/^/ /; x; /^ /! b filter'
> 
> This is unreadable and it does not work with my gcc version. I get
> dependencies like
> 
>     $(wildcard include/config/ksym/simple/strtoull [enabled by default].h) \

That's too bad.  This had almost zero overhead as the preprocessor 
didn't have to be executed twice.

Probably adding s/ .*//; before w $(1) would fix that.  But I agree this 
is fragile.  What gcc version is this?

> Please use some other way, which does not require parsing the compiler
> diagnostic messages. A straightforward solution is to do something
> similar to genksyms: A separate preprocessor pass with -Dsomething that
> leaves the EXPORT_SYMBOL statements alone and just collect their occurences.

I went that route at some point. But here I need to extract those 
EXPORT_SYMBOL() instances for all if_changed_dep uses.  That includes 
cc_o_c, cc_s_c, cc_i_c, cc_lst_c, as_s_S, as_o_S, etc. etc.  I need the 
corresponding preprocessor flags without the usual target flags.  Let's 
see what I can do that is more readable than a sed script.

Oh and who said that a sed script had to, or could be readable?  ;-)

Nicolas