linux-kernel - Re: [PATCH 10/36] AArch64: MMU definitions

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Message-ID: <20121002153939.GH25708@arm.com>
Date:	Tue, 2 Oct 2012 16:39:39 +0100
From:	Catalin Marinas <catalin.marinas@....com>
To:	Jon Masters <jonathan@...masters.org>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Arnd Bergmann <arnd@...db.de>,
	Will Deacon <Will.Deacon@....com>
Subject: Re: [PATCH 10/36] AArch64: MMU definitions

On Tue, Oct 02, 2012 at 01:43:04AM +0100, Jon Masters wrote:
> On 07/06/2012 05:05 PM, Catalin Marinas wrote:
> 
> > +/*
> > + * PAGE_OFFSET - the virtual address of the start of the kernel image.
> > + * VA_BITS - the maximum number of bits for virtual addresses.
> > + * TASK_SIZE - the maximum size of a user space task.
> > + * TASK_UNMAPPED_BASE - the lower boundary of the mmap VM area.
> > + * The module space lives between the addresses given by TASK_SIZE
> > + * and PAGE_OFFSET - it must be within 128MB of the kernel text.
> > + */
> > +#define PAGE_OFFSET		UL(0xffffffc000000000)
> > +#define MODULES_END		(PAGE_OFFSET)
> > +#define MODULES_VADDR		(MODULES_END - SZ_64M)
> > +#define VA_BITS			(39)
> > +#define TASK_SIZE_64		(UL(1) << VA_BITS)
> 
> Pedantic nit pick. Shouldn't that "it must be within 128MB of the kernel
> text" be "within 128MB of the *end* of the kernel text"? The point being
> that on AArch64 unconditional branches are encoded as imm26+1 (27 bits)
> and so you're going with -64MB to ensure that you're within the range.

I read it to be within 128MB of any part of the kernel text but I can
change it to "end of" if that's clearer.

-- 
Catalin
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