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    Subject[PATCH 21/25] dynamic_debug: protect "dyndbg" fake module param name at compile-time
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    From: Jim Cromie <jim.cromie@gmail.com>

    Add BUILD_BUG_DECL(name, cond) to cause compile error if condition is
    true. Unlike other flavors of BUILD_BUG_*, this works at file scope;
    it declares an unused 0-sized var: __BUILD_BUG_DECL_##name, whose
    declaration is readily found if compile errors happen.

    Use this macro in module_param_named() to insure that "dyndbg" is
    reserved and not used by modules as a param name, and drop the
    run-time check for same.

    Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
    ---
    include/linux/kernel.h | 10 ++++++++++
    include/linux/moduleparam.h | 1 +
    2 files changed, 11 insertions(+), 0 deletions(-)

    diff --git a/include/linux/kernel.h b/include/linux/kernel.h
    index e8b1597..f137bed 100644
    --- a/include/linux/kernel.h
    +++ b/include/linux/kernel.h
    @@ -665,6 +665,7 @@ static inline void ftrace_dump(enum ftrace_dump_mode oops_dump_mode) { }
    #define BUILD_BUG_ON_ZERO(e) (0)
    #define BUILD_BUG_ON_NULL(e) ((void*)0)
    #define BUILD_BUG_ON(condition)
    +#define BUILD_BUG_DECL(name, condition)
    #else /* __CHECKER__ */

    /* Force a compilation error if a constant expression is not a power of 2 */
    @@ -703,6 +704,15 @@ extern int __build_bug_on_failed;
    if (condition) __build_bug_on_failed = 1; \
    } while(0)
    #endif
    +/*
    + * BUILD_BUG_DECL is usable at file scope (by avoiding do {} loop).
    + * If condition is true, causes a compile error, otherwize it declares
    + * a 0-sized array (so it doesn't waste space)
    + */
    +#define BUILD_BUG_DECL(name, condition) \
    + static struct __BUILD_BUG_DECL_ ##name { \
    + int __BUILD_BUG_DECL_ ##name[1 - 2*!!(condition)]; \
    + } __BUILD_BUG_DECL_ ##name[0] __attribute__((unused))
    #endif /* __CHECKER__ */

    /* Trap pasters of __FUNCTION__ at compile-time */
    diff --git a/include/linux/moduleparam.h b/include/linux/moduleparam.h
    index 3e272c7..9e7d196 100644
    --- a/include/linux/moduleparam.h
    +++ b/include/linux/moduleparam.h
    @@ -118,6 +118,7 @@ struct kparam_array
    * structure. This allows exposure under a different name.
    */
    #define module_param_named(name, value, type, perm) \
    + BUILD_BUG_DECL(name, !__builtin_strcmp(#name, "dyndbg")); \
    param_check_##type(name, &(value)); \
    module_param_cb(name, &param_ops_##type, &value, perm); \
    __MODULE_PARM_TYPE(name, #type)
    --
    1.7.7.3


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