[Buildroot] [PATCH 2 of 7 v3] infra: add comment describing single/double dollar-sign rules
Yann E. MORIN
yann.morin.1998 at free.fr
Fri Jun 6 21:23:40 UTC 2014
Thomas, All,
On 2014-06-06 22:12 +0200, Thomas De Schampheleire spake thusly:
> As the rules with respect to variable and function references and the need
> for single or double dollar signs are not trivial, add a comment in
> pkg-generic.mk describing them.
>
> Signed-off-by: Thomas De Schampheleire <thomas.de.schampheleire at gmail.com>
Acked-by: "Yann E. MORIN" <yann.morin.1998 at free.fr>
Regards,
Yann E. MORIN.
> ---
> v3: expand exception for pkgdir and pkgname
> v2: clarify exception for pkgdir and pkgname
>
> package/pkg-generic.mk | 23 +++++++++++++++++++++++
> 1 files changed, 23 insertions(+), 0 deletions(-)
>
> diff -r b1861ead4977 -r c09add9a59c5 package/pkg-generic.mk
> --- a/package/pkg-generic.mk Thu May 08 21:53:48 2014 +0200
> +++ b/package/pkg-generic.mk Sat May 10 10:04:45 2014 +0200
> @@ -269,6 +269,29 @@
> # argument 3 is the uppercase package name, without the HOST_ prefix
> # for host packages
> # argument 4 is the type (target or host)
> +#
> +# Note about variable and function references: inside all blocks that are
> +# evaluated with $(eval), which includes all 'inner-xxx-package' blocks,
> +# specific rules apply with respect to variable and function references.
> +# - Numbered variables (parameters to the block) can be referenced with a single
> +# dollar sign: $(1), $(2), $(3), etc.
> +# - pkgdir and pkgname should be referenced with a single dollar sign too. These
> +# functions rely on 'the most recently parsed makefile' which is supposed to
> +# be the package .mk file. If we defer the evaluation of these functions using
> +# double dollar signs, then they may be evaluated too late, when other
> +# makefiles have already been parsed. One specific case is when $$(pkgdir) is
> +# assigned to a variable using deferred evaluation with '=' and this variable
> +# is used in a target rule outside the eval'ed inner block. In this case, the
> +# pkgdir will be that of the last makefile parsed by buildroot, which is not
> +# the expected value. This mechanism is for example used for the TARGET_PATCH
> +# rule.
> +# - All other variables should be referenced with a double dollar sign:
> +# $$(TARGET_DIR), $$($(2)_VERSION), etc. Also all make functions should be
> +# referenced with a double dollar sign: $$(subst), $$(call), $$(filter-out),
> +# etc. This rule ensures that these variables and functions are only expanded
> +# during the $(eval) step, and not earlier. Otherwise, unintuitive and
> +# undesired behavior occurs with respect to these variables and functions.
> +#
> ################################################################################
>
> define inner-generic-package
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