[Buildroot] [PATCH v2] Fix issue with printvars executing giant shell command

[Yann E. MORIN <yann.morin.1998@free.fr>]

Trent, All,

On 2018-09-17 11:10 -0700, Trent Piepho spake thusly:
> The underlying problem is that $(foreach V,1 2 3,) does not evaluate to
> an empty string.  It evaluates to "? ", three empty strings separated by
> whitespace.
> 
> A construct of this format, with a giant list in the foreach, is part of
> the printvars command.  This means that "@:$(foreach ....)", which is
> intended to expand to a null command, in fact expands to "@:       "
> with a great deal of whitespace.  Make chooses to execute this command
> with:
>     execve("/bin/sh", ["/bin/sh", "-c", ":       "]
> 
> But with far more whitespace.  So much that it can exceed shell command
> line length limits.
> 
> This solution is to move the foreach to another step in the recipe.  The
> "@:" is retained as the first line so the recipe is not Empty, which
> would cause a change in make behavior when make builds the target.  The
> 2nd line, all whitespace, will be skipped by make.
> 
> Signed-off-by: Trent Piepho <tpiepho@impinj.com>

Tested-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Acked-by: "Yann E. MORIN" <yann.morin.1998@free.fr>

Regards,
Yann E. MORIN.

> ---
>  Makefile | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/Makefile b/Makefile
> index 2c6af12989..57e776056c 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -988,7 +988,8 @@ $(BUILD_DIR)/.br2-external.in: $(BUILD_DIR)
>  # displayed.
>  .PHONY: printvars
>  printvars:
> -	@:$(foreach V, \
> +	@:
> +	$(foreach V, \
>  		$(sort $(if $(VARS),$(filter $(VARS),$(.VARIABLES)),$(.VARIABLES))), \
>  		$(if $(filter-out environment% default automatic, \
>  				$(origin $V)), \
> -- 
> 2.14.4
> 

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