From 1838ef1d782f7527e6defe87e180598622d2d071 Mon Sep 17 00:00:00 2001
From: "H. Peter Anvin" <hpa@zytor.com>
Date: Mon, 18 Jan 2010 14:00:34 -0800
Subject: [PATCH] x86-64, rwsem: 64-bit xadd rwsem implementation

For x86-64, 32767 threads really is not enough.  Change rwsem_count_t
to a signed long, so that it is 64 bits on x86-64.

This required the following changes to the assembly code:

a) %z0 doesn't work on all versions of gcc!  At least gcc 4.4.2 as
   shipped with Fedora 12 emits "ll" not "q" for 64 bits, even for
   integer operands.  Newer gccs apparently do this correctly, but
   avoid this problem by using the _ASM_ macros instead of %z.
b) 64 bits immediates are only allowed in "movq $imm,%reg"
   constructs... no others.  Change some of the constraints to "e",
   and fix the one case where we would have had to use an invalid
   immediate -- in that case, we only care about the upper half
   anyway, so just access the upper half.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
LKML-Reference: <tip-bafaecd11df15ad5b1e598adc7736afcd38ee13d@git.kernel.org>
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