From: Catalin Marinas <catalin.marinas@arm.com>
To: Dave Martin <Dave.Martin@arm.com>
Cc: Michael Kerrisk <mtk.manpages@gmail.com>,
linux-man@vger.kernel.org, linux-arch@vger.kernel.org,
linux-arm-kernel@lists.infradead.org,
Will Deacon <will@kernel.org>,
Vincenzo Frascino <vincenzo.frascino@arm.com>
Subject: Re: [RFC PATCH v2 6/6] prctl.2: Add tagged address ABI control prctls (arm64)
Date: Wed, 10 Jun 2020 18:42:05 +0100 [thread overview]
Message-ID: <20200610174205.GL26099@gaia> (raw)
In-Reply-To: <20200610164209.GH25945@arm.com>
On Wed, Jun 10, 2020 at 05:42:09PM +0100, Dave P Martin wrote:
> On Wed, Jun 10, 2020 at 04:26:34PM +0100, Catalin Marinas wrote:
> > On Wed, Jun 10, 2020 at 11:06:42AM +0100, Dave P Martin wrote:
> > > On Tue, Jun 09, 2020 at 06:22:32PM +0100, Catalin Marinas wrote:
> > > > On Wed, May 27, 2020 at 10:17:38PM +0100, Dave P Martin wrote:
> > > > > +.IP
> > > > > +The level of support is selected by
> > > > > +.IR "(unsigned int) arg2" ,
> > > >
> > > > We use (unsigned long) for arg2.
> > >
> > > Hmmm, not quite sure how I came up with unsigned int here. I'll just
> > > drop this: the type in the prctl() prototype is unsigned long anyway.
> > >
> > > The type is actually moot in this case, since the valid values all fit
> > > in an unsigned int.
> >
> > Passing an int doesn't require that the top 32-bit of the long are
> > zeroed (in case anyone writes the low-level SVC by hand).
>
> Fair point, I was forgetting that wrinkle. Anyway, the convention in
> this page seems to be that if the type is unsigned long, we don't
> mention it, because the prctl() prototype says that already.
>
> Question: the glibc prototype for prctl is variadic, so surely any
> calls that don't explicitly cast the args to unsigned long are already
> theoretically broken? The #defines (and 0) are all implicitly int.
> This probably affects lots of prctls.
>
> We may get away with it because the compiler is almost certainly going
> to favour a mov over a ldr for getting small integers into regs, and mov
> <Wd> fortunately zeroes the top bits for us anyway.
So does LDR Wd.
Anyway, I think glibc (or my reading of it) has something like like:
register long _x1 asm ("x1") = _x1tmp;
before invoking the SVC. I assume this would do the right conversion to
long. I can't tell about other libraries but I'd say it's their
responsibility to convert the args to long before calling the kernel's
prctl().
--
Catalin
next prev parent reply other threads:[~2020-06-10 17:42 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-27 21:17 [PATCH v2 0/6] prctl.2 man page updates for Linux 5.6 Dave Martin
2020-05-27 21:17 ` [PATCH v2 1/6] prctl.2: ffix use literal hyphens when referencing kernel docs Dave Martin
2020-05-28 6:05 ` Michael Kerrisk (man-pages)
2020-05-27 21:17 ` [PATCH v2 2/6] prctl.2: Add PR_SPEC_INDIRECT_BRANCH for SPECULATION_CTRL prctls Dave Martin
2020-05-28 7:01 ` Michael Kerrisk (man-pages)
2020-06-01 13:51 ` Dave Martin
2020-06-09 11:00 ` Michael Kerrisk (man-pages)
2020-05-27 21:17 ` [PATCH v2 3/6] prctl.2: Add PR_SPEC_DISABLE_NOEXEC " Dave Martin
2020-05-28 6:57 ` Michael Kerrisk (man-pages)
2020-05-28 13:45 ` Waiman Long
2020-05-27 21:17 ` [PATCH v2 4/6] prctl.2: Add SVE prctls (arm64) Dave Martin
2020-06-09 9:57 ` Will Deacon
2020-06-09 14:11 ` Dave Martin
2020-06-09 14:49 ` Will Deacon
2020-06-10 9:44 ` Dave Martin
2020-06-09 11:39 ` Michael Kerrisk (man-pages)
2020-06-10 9:45 ` Dave Martin
2020-05-27 21:17 ` [PATCH v2 5/6] prctl.2: Add PR_PAC_RESET_KEYS (arm64) Dave Martin
2020-06-09 10:02 ` Will Deacon
2020-06-09 11:03 ` Michael Kerrisk (man-pages)
2020-06-09 11:36 ` Michael Kerrisk (man-pages)
2020-06-09 14:16 ` Dave Martin
2020-06-09 18:11 ` Michael Kerrisk (man-pages)
2020-05-27 21:17 ` [RFC PATCH v2 6/6] prctl.2: Add tagged address ABI control prctls (arm64) Dave Martin
2020-06-09 11:04 ` Michael Kerrisk (man-pages)
2020-06-09 13:38 ` Will Deacon
2020-06-09 17:22 ` Catalin Marinas
2020-06-10 10:06 ` Dave Martin
2020-06-10 15:26 ` Catalin Marinas
2020-06-10 16:42 ` Dave Martin
2020-06-10 17:42 ` Catalin Marinas [this message]
2020-06-15 14:51 ` Dave Martin
2020-06-24 9:54 ` Michael Kerrisk (man-pages)
2020-06-24 10:29 ` Dave Martin
2020-05-28 7:11 ` [PATCH v2 0/6] prctl.2 man page updates for Linux 5.6 Michael Kerrisk (man-pages)
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