From 7742d073a434b07a72cdef5bf0eb81572e6c3a8c Mon Sep 17 00:00:00 2001 From: Thomas De Schampheleire Date: Wed, 11 Jun 2014 21:12:25 +0200 Subject: [PATCH] infra: add comment describing single/double dollar-sign rules 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 Acked-by: "Yann E. MORIN" Reviewed-by: Thomas Petazzoni Signed-off-by: Thomas Petazzoni --- package/pkg-generic.mk | 23 +++++++++++++++++++++++ 1 file changed, 23 insertions(+) diff --git a/package/pkg-generic.mk b/package/pkg-generic.mk index 3821d33917..457d873660 100644 --- a/package/pkg-generic.mk +++ b/package/pkg-generic.mk @@ -269,6 +269,29 @@ endef # 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 -- 2.30.2