Re: [PATCH v2 2/3] tpm: Address !chip->auth in tpm_buf_append_name()

["Jarkko Sakkinen" <jarkko@kernel.org>]

On Wed Jul 3, 2024 at 11:11 PM EEST, James Bottomley wrote:
> On Wed, 2024-07-03 at 21:24 +0300, Jarkko Sakkinen wrote:
> [...]
> > diff --git a/include/linux/tpm.h b/include/linux/tpm.h
> > index 21a67dc9efe8..2844fea4a12a 100644
> > --- a/include/linux/tpm.h
> > +++ b/include/linux/tpm.h
> > @@ -211,8 +211,8 @@ struct tpm_chip {
> >         u8 null_key_name[TPM2_NAME_SIZE];
> >         u8 null_ec_key_x[EC_PT_SZ];
> >         u8 null_ec_key_y[EC_PT_SZ];
> > -       struct tpm2_auth *auth;
> >  #endif
> > +       struct tpm2_auth *auth;
> >  };
>
> Since auth should only be present if CONFIG_TCG_TPM2_HMAC this is
> clearly an undesirable thing to do.  I think you did it because in a
> later patch you want to collapse the hmac sessions to use a single
> routine, but you can make that check with the preprocessor __and
> function defined in kconfig.h:
>
> if (__and(IS_ENABLED(CONFIG_TCG_TPM2_HMAC), chip->auth))
>
> Which will become 0 if the config is not enabled and chip->auth if it
> is, thus eliminating the code in the former case while not causing the
> compiler to complain about chip->auth not being defined even if it's
> under the config parameter.

I did not know about '__and()'. Thanks I'll use this!

>
> James

BR, Jarkko