Re: [RFC PATCH 01/11] prctl: Support movement of arch prctls out of common code

[Dave Martin <Dave.Martin@arm.com>]

On Mon, May 21, 2018 at 07:28:26PM +0100, Will Deacon wrote:
> Hi Dave,
> 
> On Mon, May 14, 2018 at 06:14:17PM +0100, Dave Martin wrote:
> > The core framework for the prctl() syscall is unloved and looking
> > rather crusty these days.  It also relies on defining ancillary
> > boilerplate macros for each prctl() in order to control conditional
> > compilation of the different prctl calls.  We have better ways to
> > do this now, using Kconfig.
> > 
> > This patch defines a new arch hook arch_syscall().  Architectures
> > that implemement arch-specific syscalls can now select
> > HAVE_ARCH_SYSCALL in their Kconfig and define this function
> > appropriately.
> > 
> > The core prctl() implementation now matches option against the list
> > of common or legacy prctls, deferring to prctl_arch() if an
> > unrecognised option is encountered.
> > 
> > (arch_prctl() would have been a nicer name, but it conflicts with the
> > pre-existing syscall of the same name on x86, particularly in the um
> > code.)
> > 
> > No functional change.
> 
> [...]
> 
> > diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h
> > index af5f8c2..c911ff0 100644
> > --- a/include/uapi/linux/prctl.h
> > +++ b/include/uapi/linux/prctl.h
> > @@ -1,6 +1,6 @@
> >  /* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
> > -#ifndef _LINUX_PRCTL_H
> > -#define _LINUX_PRCTL_H
> > +#ifndef _UAPI_LINUX_PRCTL_H
> > +#define _UAPI_LINUX_PRCTL_H
> 
> Is it safe to rename this #define, or is there a possibility that userspace
> could be using it for something and relying on it not changing?
> 
> Other than that:
> 
> Acked-by: Will Deacon <will.deacon@arm.com>

I think that header guards are generally viewed as being private to a
project and not API.  codesearch.debian.net yields few hits, where there
are actual #ifdefs on this symbol, they seem to be pastes of the kernel
headers:

https://codesearch.debian.net/search?q=_LINUX_PRCTL_H&perpkg=1

 -> android, linux, dietlibc ... gnome-chess (?)


There is plenty of precedent in the Howells special:

607ca46e97a1 ("UAPI: (Scripted) Disintegrate include/linux")

See for example <{,uapi/}linux/loop.h>.

Cheers
---Dave