linux-kernel - Re: [PATCH v2 16/31] arm64: ELF definitions

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Message-Id: <201208212017.08110.arnd@arndb.de>
Date:	Tue, 21 Aug 2012 20:17:07 +0000
From:	Arnd Bergmann <arnd@...db.de>
To:	Catalin Marinas <catalin.marinas@....com>
Cc:	Will Deacon <Will.Deacon@....com>,
	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 16/31] arm64: ELF definitions

On Tuesday 21 August 2012, Catalin Marinas wrote:
> On Thu, Aug 16, 2012 at 01:37:53PM +0100, Arnd Bergmann wrote:
> > On Thursday 16 August 2012, Will Deacon wrote:
> > > > This looks wrong: PER_LINUX/PER_LINUX32 decides over the output of the
> > > > uname system call, while TIF_32BIT decides over the instruction set
> > > > when returning to user space. You definitely should not set the personality
> > > > to the value you pass from the elf loader. Instead, just do
> > > > 
> > > > #define SET_PERSONALITY(ex) clear_thread_flag(TIF_32BIT);
> > > > #defined COMPAT_SET_PERSONALITY(ex) set_thread_flag(TIF_32BIT);
> > > 
> > > In this case, won't uname be incorrect (aarch64l) for aarch32 tasks (which
> > > expect something like armv8l)?
> > 
> > No, the uname output is meant to tell you about the system, not the
> > instruction set that you are using (you already know that in compiled
> > code).
> 
> OK, so we assumed that compat tasks should get a uname as close as
> possible to a 32-bit system, i.e. armv8l, for full compatibility. This
> would allow us to run something like 32-bit Debian on an AArch64 kernel
> without worrying about any scripts failing.

You can still do that, just boot with init="/sbin/setarch armv7 /sbin/init".

> But I can see on x86 that it always reports x86_64 even if the task is
> x86_32.

Not just x86, the same behavior is used on powerpc, s390, mips, sparc and
parisc. Not sure about tile though.

	Arnd
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