#382 Technical trick with CONST_OPTION macro produces faulty code

[Elena Chernikova]

Hello!
We have noticed that technical trick with CONST_OPTION macro in options.h can give rise to faulty results.

Considering the example from main.c:

...
/* Included from options.h */
extern const /* CONST_OPTION */ optionValues Option;
...
static void makeTags (cookedArgs *args)
{
...
        <read Option.recurse>
...
}

extern int main (int __unused__ argc, char **argv)
{
...
        /* Modification of Option.recurse inside parseOptions */
        parseOptions (args);
...
        makeTags (args);
...
}

A compiler can perform an inline expansion of the function 'makeTags' into the function 'main' with the following code:

...
/* Included from option.h */
extern const /* CONST_OPTION */ optionValues Option;
...
extern int main (int __unused__ argc, char **argv)
{
...
        /* Modification of Option.recurse inside */
        parseOptions (args);
...
        /* Inlined from makeTags */
        <read Option.recurse>
...
}

As far as variable named 'Option' is defined with 'const' qualificator (using CONST_OPTION), the compiler can move "read Option.recurse" higher than "call parseOptions" while optimization.
This case can be illustrated with the following code:

extern int main (int __unused__ argc, char **argv)
{
...
        <read Option.recurse>
...
        /* Modification of Option.recurse inside */
        parseOptions (args);
...
}

This code will work irregularly. For instance, with lcc compiler for Elbrus hardware platform (e2k). For correct code compiling CONST_OPTION macro should be blank. We recommend you to stop using CONST_OPTION macro.