Message-ID: <5306CB60.3070302@zytor.com>
Date: Thu, 20 Feb 2014 19:43:28 -0800
From: "H. Peter Anvin" <hpa@zytor.com>
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To: Brian Gerst <brgerst@gmail.com>,
        Linus Torvalds <torvalds@linux-foundation.org>
CC: Ingo Molnar <mingo@kernel.org>, Thomas Gleixner <tglx@linutronix.de>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Ross Zwisler <ross.zwisler@linux.intel.com>,
        "H.J. Lu" <hjl.tools@gmail.com>, Rusty Russell <rusty@rustcorp.com.au>
Subject: Re: "m" constraints, jumps, and alternatives
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On 02/20/2014 07:30 PM, Brian Gerst wrote:
> 
> The percpu code uses %P to force absolute addressing mode, instead of
> rip-relative.
> 

   P -- if PIC, print an @PLT suffix.

Clearly it has more effects than that... as the code does reveal:

      /* Avoid (%rip) for call operands.  */
      if (CONSTANT_ADDRESS_P (x) && code == 'P'
          && !CONST_INT_P (x))

That should work... in the probably extremely rare case that any of
these references go to global addresses then they spend an extra byte
(and a little more work during kASLR relocation or module insertion).

	-hpa

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