kconfig: error out if a recursive variable references itself
When using a recursively expanded variable, it is a common mistake to make circular reference. For example, Make terminates the following code: X = $(X) Y := $(X) Let's detect the circular expansion in Kconfig, too. On the other hand, a function that recurses itself is a commonly-used programming technique. So, Make does not check recursion in the reference with 'call'. For example, the following code continues running eternally: X = $(call X) Y := $(X) Kconfig allows circular expansion if one or more arguments are given, but terminates when the same function is recursively invoked 1000 times, assuming it is a programming mistake. Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
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@ -229,6 +229,7 @@ struct variable {
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char *name;
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char *value;
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enum variable_flavor flavor;
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int exp_count;
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struct list_head node;
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};
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@ -253,11 +254,22 @@ static char *variable_expand(const char *name, int argc, char *argv[])
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if (!v)
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return NULL;
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if (argc == 0 && v->exp_count)
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pperror("Recursive variable '%s' references itself (eventually)",
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name);
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if (v->exp_count > 1000)
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pperror("Too deep recursive expansion");
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v->exp_count++;
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if (v->flavor == VAR_RECURSIVE)
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res = expand_string_with_args(v->value, argc, argv);
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else
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res = xstrdup(v->value);
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v->exp_count--;
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return res;
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}
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@ -284,6 +296,7 @@ void variable_add(const char *name, const char *value,
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v = xmalloc(sizeof(*v));
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v->name = xstrdup(name);
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v->exp_count = 0;
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list_add_tail(&v->node, &variable_list);
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}
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