[PATCH v4 18/31] kconfig: error out if a recursive variable references itself

Masahiro Yamada
2018-05-17T06:19:16Z

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>
---

Changes in v4:
- Newly added

Changes in v3: None
Changes in v2: None

scripts/kconfig/preprocess.c | 13 +++++++++++++
1 file changed, 13 insertions(+)

diff --git a/scripts/kconfig/preprocess.c b/scripts/kconfig/preprocess.c
index c39e30e..246f879 100644
--- a/scripts/kconfig/preprocess.c
+++ b/scripts/kconfig/preprocess.c
@@ -276,6 +276,7 @@ struct variable {
char *name;
char *value;
enum variable_flavor flavor;
+ int exp_count;
struct list_head node;
};

@@ -306,8 +307,19 @@ static char *variable_expand(const char *name, int argc, char *argv[],
expanded_argv[i] = expand_string_with_args(argv[i],
old_argc, old_argv);

+ if (argc == 0 && v->exp_count)
+ pperror("Recursive variable '%s' references itself (eventually)",
+ name);
+
+ if (v->exp_count > 1000)
+ pperror("Too deep recursive expansion");
+
+ v->exp_count++;
+
res = expand_string_with_args(v->value, argc, expanded_argv);

+ v->exp_count--;
+
for (i = 0; i < argc; i++)
free(expanded_argv[i]);

@@ -337,6 +349,7 @@ void variable_add(const char *name, const char *value,

v = xmalloc(sizeof(*v));
v->name = xstrdup(name);
+ v->exp_count = 0;
list_add_tail(&v->node, &variable_list);
}

--
2.7.4