34 lines
1.3 KiB
Makefile
34 lines
1.3 KiB
Makefile
# $NetBSD: varmod-loop-delete.mk,v 1.2 2021/12/05 15:51:33 rillig Exp $
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#
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# Tests for the variable modifier ':@', which as a side effect allows to
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# delete an arbitrary variable.
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# A side effect of the modifier ':@' is that the loop variable is created as
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# an actual variable in the current evaluation scope (Command/Global/target),
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# and at the end of the loop, this variable is deleted. Since var.c 1.204
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# from 2016-02-18 and before var.c 1.963 from 2021-12-05, a variable could be
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# deleted while it was in use, leading to a use-after-free bug.
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#
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# See Var_Parse, comment 'the value of the variable must not change'.
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# Set up the variable that deletes itself when it is evaluated.
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VAR= ${:U:@VAR@@} rest of the value
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# In an assignment, the scope is 'Global'. Since the variable 'VAR' is
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# defined in the global scope, it deletes itself.
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EVAL:= ${VAR}
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.if ${EVAL} != " rest of the value"
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. error
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.endif
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VAR= ${:U:@VAR@@} rest of the value
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all: .PHONY
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# In the command that is associated with a target, the scope is the
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# one from the target. That scope only contains a few variables like
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# '.TARGET', '.ALLSRC', '.IMPSRC'. Make does not expect that these
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# variables get modified from the outside.
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#
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# There is no variable named 'VAR' in the local scope, so nothing
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# happens.
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: $@: '${VAR}'
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