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

Nicolas Pitre
2016-03-04T02:46:42Z

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