From: Nick Desaulniers <ndesaulniers@google.com>
To: denkenz@gmail.com
Cc: jejb@linux.ibm.com, dhowells@redhat.com,
Nathan Chancellor <natechancellor@gmail.com>,
Eric Biggers <ebiggers@google.com>,
zohar@linux.vnet.ibm.com, jmorris@namei.org, serge@hallyn.com,
linux-integrity@vger.kernel.org, keyrings@vger.kernel.org,
linux-security-module@vger.kernel.org,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] KEYS: trusted: fix -Wvarags warning
Date: Fri, 12 Oct 2018 10:17:50 -0700 [thread overview]
Message-ID: <CAKwvOdnRJtHEUf-2kObUiUCc_ZPRdYHxMft3s1YE6=9EnHYMMg@mail.gmail.com> (raw)
In-Reply-To: <CAKwvOdmStDm3Lz=W7XjmB7f7ihe4hLOmaBRLOrStbkBMRKwdjA@mail.gmail.com>
On Fri, Oct 12, 2018 at 10:05 AM Nick Desaulniers
<ndesaulniers@google.com> wrote:
>
> On Fri, Oct 12, 2018 at 8:14 AM Denis Kenzior <denkenz@gmail.com> wrote:
> >
> > Hi James,
> >
> > >> So can't we simply use 'bool' or uint32 as the type for h3 instead
> > >> of re-ordering everything
> > >
> > > The problem is the standard is ambiguious. The only thing that's
> > > guaranteed to work for all time is a char *. If you want to keep the
> > > order, what I'd suggest is inserting a dummy pointer argument which is
> > > always expected to be NULL between the h3 and the varargs.
> >
> > So maybe I'm misunderstanding something, but the issue seems to be that
> > unsigned char is promoted to 'unsigned char *' by Clang and probably
> > unsigned int or int by gcc.
>
> No. This is extremely well defined behavior in C. In C, integral
> types are NEVER promoted to pointer to integer types, only to larger
> integral types through rules more complicated than the correct flags
> to pass to `tar`.
> https://xkcd.com/1168/
And may have their signedness converted.
https://wiki.sei.cmu.edu/confluence/display/c/INT02-C.+Understand+integer+conversion+rules
is the reference I use, though I always feel like there's quite a bit
of mental gymnastics involved interpreting it.
>
> >
> > So instead of having unsigned char h3, can't we simply have bool h3 or
> > unsigned int h3?
>
> int is the default argument promotion. Proposed:
> https://github.com/ClangBuiltLinux/linux/issues/41#issuecomment-428365339
>
> >
> > Regards,
> > -Denis
> >
>
>
> --
> Thanks,
> ~Nick Desaulniers
--
Thanks,
~Nick Desaulniers
next prev parent reply other threads:[~2018-10-12 17:18 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-09 22:11 undefined behavior (-Wvarargs) in security/keys/trusted.c#TSS_authhmac() Nick Desaulniers
2018-10-11 16:02 ` Arnd Bergmann
2018-10-11 16:10 ` James Bottomley
2018-10-11 20:31 ` [PATCH] KEYS: trusted: fix -Wvarags warning ndesaulniers
2018-10-12 1:50 ` Nathan Chancellor
2018-10-12 16:55 ` Nick Desaulniers
2018-10-12 17:03 ` Nathan Chancellor
2018-10-12 12:29 ` Denis Kenzior
2018-10-12 15:05 ` James Bottomley
2018-10-12 15:13 ` Denis Kenzior
2018-10-12 15:22 ` James Bottomley
2018-10-12 15:44 ` Denis Kenzior
2018-10-12 15:46 ` James Bottomley
2018-10-12 15:53 ` Denis Kenzior
2018-10-12 16:01 ` James Bottomley
2018-10-12 17:14 ` Nick Desaulniers
2018-10-12 15:25 ` James Bottomley
2018-10-12 17:05 ` Nick Desaulniers
2018-10-12 17:17 ` Nick Desaulniers [this message]
2018-10-12 17:27 ` Denis Kenzior
2018-10-12 18:39 ` Nick Desaulniers
2018-10-12 17:02 ` Nick Desaulniers
2018-10-12 17:15 ` Denis Kenzior
2018-10-15 9:26 ` David Laight
2018-10-15 21:53 ` Nick Desaulniers
2018-10-16 8:13 ` David Laight
2018-10-22 23:43 ` [PATCH v2] " ndesaulniers
2018-10-23 0:00 ` Nathan Chancellor
2018-10-24 8:36 ` Jarkko Sakkinen
2018-10-29 17:54 ` Nick Desaulniers
2019-02-11 18:36 ` Nick Desaulniers
2019-02-12 23:12 ` Jarkko Sakkinen
2019-02-14 10:52 ` Jarkko Sakkinen
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