Re: [Buildroot] [PATCHv2] Makefile: fix show-vars for good this time

[Thomas Petazzoni via buildroot <buildroot@buildroot.org>]

On Mon,  1 Aug 2022 22:42:27 +0200
"Yann E. MORIN" <yann.morin.1998@free.fr> wrote:

> Commit 5c54c3ef3db2 (Makefile: workaround make 4.3 issue for 'printvars
> and 'show-vars') did not fully fix the show-vars case, which still
> segfaults.
> 
> Overall, show-vars generates a JSON blurb. That is supposed to be
> machine-readable, so we do not care that the variables are sorted, so
> we get rid of it to (slightly) simplify the code.
> 
> Then, we currently iterate twice on the list of variables: the first one
> to filter-out the 'internal' variables, and the second one to filter
> only the variables matching the pattern. We can do away by iterating
> only once, and applying both filters at once.
> 
> Since we now have an 'and' condition, we can take advantage of it: when
> none of the items in $(and) are empty, $(and) evaluates to the last
> item, while it evaluates to empty if any of the items is empty. So we
> can coalesce the $(if) and $(and) together: $(if $(and a,b),c) is
> equivalent to: $(and a,b,c) ; this gains us one parentheses depth.
> 
> Finally, the cause for the segfault is an overly-long call to $(info).
> Reducing that is not easy: we want to call clean-json on the whole of
> the JSON blurb, so we can't emit the individual variables one by one, or
> the trailing comma would not be trimmed away.
> 
> So, we go crazy: we just output each word from clean-json with $(info).
> 
> We can do that, because mk-json-str transforms all spaces in a string
> to an escaped UTF-8 sequence, so we will never have spaces in values;
> the keys are the variables, so they won't have spaces either; spaces in
> the rest of the JSON blurb are totally optional, so we don't care how
> many there are. We know there are spaces, because we explicitly
> introduce some (after "expanded" or "raw", for example), so we should
> never hit a too-big word for $(info) to print.
> 
> Thanks to Henri for the suggestion to push $(info) further inside the
> macro.
> 
> Reported-by: Quentin Schulz <quentin.schulz@theobroma-systems.com>
> Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
> Cc: Roosen Henri <Henri.Roosen@ginzinger.com>
> Cc: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
> Cc: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
> 
> ---
> Changes v1 -> v2:
>   - coalesce $(if) with $(and)
>   - don't output a trailing $(space) when calling $(info)
> ---
>  Makefile | 15 +++++++++++----
>  1 file changed, 11 insertions(+), 4 deletions(-)

Applied to master, thanks.

Thomas
-- 
Thomas Petazzoni, CTO, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com
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