Neither -Wunused-result, nor --warn-unused-result generates warnings about unused results

Question

This (simplest-example) program is set up so main() calls the makeKey() function and fails to check the return value ...Which demonstrates why, when programming, especially security critical code [I'm looking at you Sony], it is important to check your return values.

[demo.c]
int makeKey (void) {  /* returns 0/false if there is an error */
    /* //! todo - just return an error for now [fred@sony] */
    return 0;
}

int main() {
    makeKey();  /* make a new key for the crypto */
    return 0;   /* return 0=success              */
}

I want my compiler (gcc version 12.2.0) to "complain" with a warning/error message such as: "return value not used"

It doesn't seem to matter what switches I add to gcc, it seems happy to ignore this easily-detected mistake ...After reading maaany articles, I've got this far:

gcc -Werror -Wall -Wextra -Wunused-result --warn-unused-result -pedantic-errors -ansi -std=c99 demo.c

...But still no luck!

I have discovered that I can make each function "opt-in" to this sanity/security check with:

int makeKey (void) __attribute__ ((warn_unused_result)) {  // returns 0 if there is an error

But I want the security to be enabled by default (with an attribute that allows you to "opt-out", eg. printf())

• Is this even possible with a standard install of gcc v12?
• If so, what command line switch am I missing?