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 17:17:50 +0000 [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
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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 17:17 UTC|newest] Thread overview: 68+ 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 2018-10-09 22:11 ` Nick Desaulniers 2018-10-11 16:02 ` Arnd Bergmann 2018-10-11 16:02 ` Arnd Bergmann 2018-10-11 16:10 ` James Bottomley 2018-10-11 16:10 ` James Bottomley 2018-10-11 20:31 ` [PATCH] KEYS: trusted: fix -Wvarags warning ndesaulniers 2018-10-11 20:31 ` ndesaulniers 2018-10-12 1:50 ` Nathan Chancellor 2018-10-12 1:50 ` Nathan Chancellor 2018-10-12 16:55 ` Nick Desaulniers 2018-10-12 16:55 ` Nick Desaulniers 2018-10-12 17:03 ` Nathan Chancellor 2018-10-12 17:03 ` Nathan Chancellor 2018-10-12 12:29 ` Denis Kenzior 2018-10-12 12:29 ` Denis Kenzior 2018-10-12 15:05 ` James Bottomley 2018-10-12 15:05 ` James Bottomley 2018-10-12 15:13 ` Denis Kenzior 2018-10-12 15:13 ` Denis Kenzior 2018-10-12 15:22 ` James Bottomley 2018-10-12 15:22 ` James Bottomley 2018-10-12 15:44 ` Denis Kenzior 2018-10-12 15:44 ` Denis Kenzior 2018-10-12 15:46 ` James Bottomley 2018-10-12 15:46 ` James Bottomley 2018-10-12 15:53 ` Denis Kenzior 2018-10-12 15:53 ` Denis Kenzior 2018-10-12 16:01 ` James Bottomley 2018-10-12 16:01 ` James Bottomley 2018-10-12 17:14 ` Nick Desaulniers 2018-10-12 17:14 ` Nick Desaulniers 2018-10-12 15:25 ` James Bottomley 2018-10-12 15:25 ` James Bottomley 2018-10-12 17:05 ` Nick Desaulniers 2018-10-12 17:05 ` Nick Desaulniers 2018-10-12 17:17 ` Nick Desaulniers [this message] 2018-10-12 17:17 ` Nick Desaulniers 2018-10-12 17:27 ` Denis Kenzior 2018-10-12 17:27 ` Denis Kenzior 2018-10-12 18:39 ` Nick Desaulniers 2018-10-12 18:39 ` Nick Desaulniers 2018-10-12 17:02 ` Nick Desaulniers 2018-10-12 17:02 ` Nick Desaulniers 2018-10-12 17:15 ` Denis Kenzior 2018-10-12 17:15 ` Denis Kenzior 2018-10-15 9:26 ` David Laight 2018-10-15 9:26 ` David Laight 2018-10-15 9:26 ` David Laight 2018-10-15 21:53 ` Nick Desaulniers 2018-10-15 21:53 ` Nick Desaulniers 2018-10-16 8:13 ` David Laight 2018-10-16 8:13 ` David Laight 2018-10-16 8:13 ` David Laight 2018-10-22 23:43 ` [PATCH v2] " ndesaulniers 2018-10-22 23:43 ` ndesaulniers 2018-10-23 0:00 ` Nathan Chancellor 2018-10-23 0:00 ` Nathan Chancellor 2018-10-24 8:36 ` Jarkko Sakkinen 2018-10-24 8:36 ` Jarkko Sakkinen 2018-10-29 17:54 ` Nick Desaulniers 2018-10-29 17:54 ` Nick Desaulniers 2019-02-11 18:36 ` Nick Desaulniers 2019-02-11 18:36 ` Nick Desaulniers 2019-02-12 23:12 ` Jarkko Sakkinen 2019-02-12 23:12 ` Jarkko Sakkinen 2019-02-14 10:52 ` Jarkko Sakkinen 2019-02-14 10:52 ` Jarkko Sakkinen
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