From: David Daney <ddaney@caviumnetworks.com>
To: Alexandre Oliva <aoliva@redhat.com>
Cc: linux-mips <linux-mips@linux-mips.org>, GCC <gcc@gcc.gnu.org>,
binutils <binutils@sourceware.org>,
Prasun Kapoor <prasun.kapoor@caviumnetworks.com>
Subject: Re: RFC: A new MIPS64 ABI
Date: Tue, 15 Feb 2011 18:08:00 -0000 [thread overview]
Message-ID: <4D5AC12D.3080108@caviumnetworks.com> (raw)
In-Reply-To: <orzkpx6v2m.fsf@livre.localdomain>
On 02/15/2011 09:56 AM, Alexandre Oliva wrote:
> On Feb 14, 2011, David Daney<ddaney@caviumnetworks.com> wrote:
>
>> Current MIPS 32-bit ABIs (both o32 and n32) are restricted to 2GB of
>> user virtual memory space. This is due the way MIPS32 memory space is
>> segmented. Only the range from 0..2^31-1 is available. Pointer
>> values are always sign extended.
>
>> The proposed new ABI would only be available on MIPS64 platforms. It
>> would be identical to the current MIPS n32 ABI *except* that pointers
>> would be zero-extended rather than sign-extended when resident in
>> registers.
>
> FTR, I don't really know why my Yeeloong is limited to 31-bit addresses,
> and I kind of hoped an n32 userland would improve that WRT o32, without
> wasting memory with longer pointers like n64 would.
>
> So, sorry if this is a dumb question, but wouldn't it be much easier to
> keep on using sign-extended addresses, and just make sure the kernel
> never allocates a virtual memory range that crosses a sign-bit change,
> or whatever other reason there is for addresses to be limited to the
> positive 2GB range in n32?
>
No, it is not possible. The MIPS (and MIPS64) hardware architecture
does not allow userspace access to addresses with the high bit (two bits
for mips64) set.
Your complaint is a good summary of why I am thinking about n32-big.
David Daney
next prev parent reply other threads:[~2011-02-15 18:08 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-02-14 20:29 David Daney
2011-02-15 0:15 ` Matt Thomas
2011-02-15 1:57 ` Paul Koning
2011-02-15 2:15 ` Joe Buck
2011-02-15 2:16 ` Paul Koning
2011-02-15 2:26 ` David Daney
2011-02-15 2:35 ` Matt Thomas
2011-02-15 2:43 ` David Daney
2011-02-15 17:33 ` Joseph S. Myers
2011-02-15 18:15 ` David Daney
2011-02-15 2:22 ` David Daney
2011-02-15 2:33 ` Matt Thomas
2011-02-15 2:50 ` David Daney
2011-02-15 3:02 ` Matt Thomas
2011-02-15 17:41 ` David Daney
2011-02-15 17:48 ` Paul Koning
2011-02-15 17:56 ` Alexandre Oliva
2011-02-15 18:08 ` David Daney [this message]
2011-05-06 8:31 ` Alexandre Oliva
2011-05-06 17:00 ` David Daney
2011-02-18 1:02 ` David Daney
[not found] <4D5990A4.2050308__41923.1521235362$1297715435$gmane$org@caviumnetworks.com>
2011-02-21 19:45 ` Richard Sandiford
2011-05-09 14:27 ` Ralf Baechle
2011-05-09 17:47 ` David Daney
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