On Wed, 3 Jul 2024 at 13:11, James Bottomley James.Bottomley@hansenpartnership.com wrote:
if (__and(IS_ENABLED(CONFIG_TCG_TPM2_HMAC), chip->auth))
Augh. Please don't do this.
That "__and()" thing may work, but it's entirely accidental that it does.
It's designed for config options _only_, and the fact that it then happens to work for "first argument is config option, second argument is C conditional".
The comment says that it's implementing "&&" using preprocessor expansion only, but it's a *really* limited form of it. The arguments are *not* arbitrary.
So no. Don't do this.
Just create a helper inline like
static inline struct tpm2_auth *chip_auth(struct tpm_chip *chip) { #ifdef CONFIG_TCG_TPM2_HMAC return chip->auth; #else return NULL; #endif }
and if we really want to have some kind of automatic way of doing this, we will *NOT* be using __and(), we'd do something like
/* Return zero or 'value' depending on whether OPTION is enabled or not */ #define IF_ENABLED(option, value) __and(IS_ENABLED(option), value)
that actually would be documented and meaningful.
Not this internal random __and() implementation that is purely a kconfig.h helper macro and SHOULD NOT be used anywhere else.
Linus