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From f5b973489beb1a1239dfad53e3ad6e36ff7ee958 Mon Sep 17 00:00:00 2001
From: Segher Boessenkool <segher@kernel.crashing.org>
Date: Thu, 9 Oct 2008 21:18:27 +0100
Subject: [PATCH] fix-gcc-4.3-false-modulo-optimization.patch
I tried to compile the current stable kernel
(a2ef813d2f439a3e9f377d33a2e5baad098afb7e)
and get the following errors:
kernel/built-in.o: In function `timespec_add_ns':
/mnt/data/Freerunner/Gentoo/rootinstall/usr/src/linux/include/linux/time.h:174:
undefined reference to `__aeabi_uldivmod'
/mnt/data/Freerunner/Gentoo/rootinstall/usr/src/linux/include/linux/time.h:179:
undefined reference to `__aeabi_uldivmod'
/mnt/data/Freerunner/Gentoo/rootinstall/usr/src/linux/include/linux/time.h:174:
undefined reference to `__aeabi_uldivmod'
/mnt/data/Freerunner/Gentoo/rootinstall/usr/src/linux/include/linux/time.h:179:
undefined reference to `__aeabi_uldivmod'
applying the following patch solved the problem:
--------
Prevent gcc-4.3 form "optimizing" the while loop into a costly modulo operation.
Patch found at http://lkml.org/lkml/2008/2/22/464.
Reported-by: Sven Rebhan <odinshorse@googlemail.com>
Signed-off-by: Segher Boessenkool <segher@kernel.crashing.org>
---
include/linux/time.h | 4 ++++
1 files changed, 4 insertions(+), 0 deletions(-)
diff --git a/include/linux/time.h b/include/linux/time.h
index b04136d..3e8fd9e 100644
--- a/include/linux/time.h
+++ b/include/linux/time.h
@@ -173,6 +173,10 @@ static inline void timespec_add_ns(struct timespec *a, u64 ns)
{
ns += a->tv_nsec;
while(unlikely(ns >= NSEC_PER_SEC)) {
+ /* The following asm() prevents the compiler from
+ * optimising this loop into a modulo operation. */
+ asm("" : "+r"(ns));
+
ns -= NSEC_PER_SEC;
a->tv_sec++;
}
--
1.5.6.5
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