Skip to main content

Browse the archive

https://github.com/torvalds/linux
13 June 2022, 11:31:42 UTC
Revision bdbc29c19b2633b1d9c52638fb732bcde7a2031a authored by Paul Mackerras on 27 August 2013, 06:07:49 UTC, committed by Benjamin Herrenschmidt on 27 August 2013, 06:59:30 UTC 
powerpc: Work around gcc miscompilation of __pa() on 64-bit
 
On 64-bit, __pa(&static_var) gets miscompiled by recent versions of
gcc as something like:

        addis 3,2,.LANCHOR1+4611686018427387904@toc@ha
        addi 3,3,.LANCHOR1+4611686018427387904@toc@l

This ends up effectively ignoring the offset, since its bottom 32 bits
are zero, and means that the result of __pa() still has 0xC in the top
nibble.  This happens with gcc 4.8.1, at least.

To work around this, for 64-bit we make __pa() use an AND operator,
and for symmetry, we make __va() use an OR operator.  Using an AND
operator rather than a subtraction ends up with slightly shorter code
since it can be done with a single clrldi instruction, whereas it
takes three instructions to form the constant (-PAGE_OFFSET) and add
it on.  (Note that MEMORY_START is always 0 on 64-bit.)

CC: <stable@vger.kernel.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
1 parent f5f6cbb
Raw File
Tip revision: bdbc29c19b2633b1d9c52638fb732bcde7a2031a authored by Paul Mackerras on 27 August 2013, 06:07:49 UTC
powerpc: Work around gcc miscompilation of __pa() on 64-bit
Tip revision: bdbc29c
uuid.c 
/*
 * Unified UUID/GUID definition
 *
 * Copyright (C) 2009, Intel Corp.
 *	Huang Ying <ying.huang@intel.com>
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License version
 * 2 as published by the Free Software Foundation;
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

#include <linux/kernel.h>
#include <linux/export.h>
#include <linux/uuid.h>
#include <linux/random.h>

static void __uuid_gen_common(__u8 b[16])
{
	prandom_bytes(b, 16);
	/* reversion 0b10 */
	b[8] = (b[8] & 0x3F) | 0x80;
}

void uuid_le_gen(uuid_le *lu)
{
	__uuid_gen_common(lu->b);
	/* version 4 : random generation */
	lu->b[7] = (lu->b[7] & 0x0F) | 0x40;
}
EXPORT_SYMBOL_GPL(uuid_le_gen);

void uuid_be_gen(uuid_be *bu)
{
	__uuid_gen_common(bu->b);
	/* version 4 : random generation */
	bu->b[6] = (bu->b[6] & 0x0F) | 0x40;
}
EXPORT_SYMBOL_GPL(uuid_be_gen);
back to top