From: Dave Martin <Dave.Martin@arm.com>
To: Dave Hansen <dave.hansen@intel.com>
Cc: linux-arch@vger.kernel.org, linux-doc@vger.kernel.org,
Szabolcs Nagy <szabolcs.nagy@arm.com>,
Catalin Marinas <catalin.marinas@arm.com>,
Kevin Brodsky <kevin.brodsky@arm.com>,
Will Deacon <will.deacon@arm.com>,
Andrey Konovalov <andreyknvl@google.com>,
Vincenzo Frascino <vincenzo.frascino@arm.com>,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v7 1/2] arm64: Define Documentation/arm64/tagged-address-abi.rst
Date: Thu, 8 Aug 2019 17:27:02 +0100 [thread overview]
Message-ID: <20190808162702.GJ10425@arm.com> (raw)
In-Reply-To: <826a9ace-feac-c019-843e-07e23c9fd46c@intel.com>
On Wed, Aug 07, 2019 at 01:38:16PM -0700, Dave Hansen wrote:
[Random comments below on a couple of points]
> On 8/7/19 8:53 AM, Catalin Marinas wrote:
> > +- mmap() done by the process itself (or its parent), where either:
> > +
> > + - flags have the **MAP_ANONYMOUS** bit set
> > + - the file descriptor refers to a regular file (including those returned
> > + by memfd_create()) or **/dev/zero**
>
> What's a "regular file"? ;)
A file, as distinct from device nodes, sockets, symlinks etc.
I think this is fairly standard UNIX terminology, even though it sounds
vague:
From glibc's <bits/stat.h>:
#define __S_IFREG 0100000 /* Regular file. */
Or for POSIX test (a.k.a. "[")
-f file
True if file exists and is a regular file.
Using memfd_create() or opening /dev/zero doesn't yield a regular file
though, so perhaps those should be a separate bullet.
[...]
> > +The AArch64 Tagged Address ABI is an opt-in feature and an application can
> > +control it via **prctl()** as follows:
> > +
> > +- **PR_SET_TAGGED_ADDR_CTRL**: enable or disable the AArch64 Tagged Address
> > + ABI for the calling process.
> > +
> > + The (unsigned int) arg2 argument is a bit mask describing the control mode
> > + used:
> > +
> > + - **PR_TAGGED_ADDR_ENABLE**: enable AArch64 Tagged Address ABI. Default
> > + status is disabled.
> > +
> > + The arguments arg3, arg4, and arg5 are ignored.
>
> For previous prctl()'s, we've found that it's best to require that the
> unused arguments be 0. Without that, apps are free to put garbage
> there, which makes extending the prctl to use other arguments impossible
> in the future.
Because arg2 is already a mask of flags with some flags unallocated,
we can add a new flag for ABI extensions.
If arg3 is used someday, it may or may not be natural for 0 to mean
"default". Enabling this argument with an explicit flag in arg2 may
be cleaner than mangling the semantics of arg3 so that 0 can have
the right meaning.
Avoiding redundant 0 arguments also allows userspace to take advantage
of the glibc's variadic prototype for prctl() for example.
Not a huge deal, but that was my rationale anyway.
> Also, shouldn't this be converted over to an arch_prctl()?
Most arch-specific prctls seem to use prctl(), and arm64 already has a
few there.
arch_prctl() is x86-specific. I don't know the history.
[...]
Cheers
---Dave
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next prev parent reply other threads:[~2019-08-08 16:27 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-07 15:53 [PATCH v7 0/2] arm64 tagged address ABI Catalin Marinas
2019-08-07 15:53 ` [PATCH v7 1/2] arm64: Define Documentation/arm64/tagged-address-abi.rst Catalin Marinas
2019-08-07 20:38 ` Dave Hansen
2019-08-08 9:25 ` Szabolcs Nagy
2019-08-08 16:20 ` Szabolcs Nagy
2019-08-08 16:27 ` Dave Martin [this message]
2019-08-08 17:27 ` Catalin Marinas
2019-08-09 14:10 ` Dave Hansen
2019-08-12 17:36 ` Catalin Marinas
2019-08-13 11:10 ` Dave Martin
2019-08-08 16:30 ` Szabolcs Nagy
2019-08-08 17:04 ` Will Deacon
2019-08-12 10:46 ` Andrew Murray
2019-08-12 17:17 ` Catalin Marinas
2019-08-07 15:53 ` [PATCH v7 2/2] arm64: Relax Documentation/arm64/tagged-pointers.rst Catalin Marinas
2019-08-08 17:06 ` Will Deacon
2019-08-08 9:32 ` [PATCH v7 0/2] arm64 tagged address ABI Szabolcs Nagy
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