After reading the mail, it seems I should give the compilation error log to make the question crisp. So here it is:
> kernel/built-in.o: In function `getnstimeofday':
> (.text+0x22bdc): undefined reference to `__umoddi3'
> kernel/built-in.o: In function `getnstimeofday':
> (.text+0x22bfc): undefined reference to `__udivdi3'
> kernel/built-in.o: In function `do_gettimeofday':
> (.text+0x22d0e): undefined reference to `__udivdi3'
> kernel/built-in.o: In function `do_gettimeofday':
> (.text+0x22d2c): undefined reference to `__umoddi3'
> kernel/built-in.o: In function `timekeeping_resume':
> timekeeping.c:(.text+0x22fd4): undefined reference to `__umoddi3'
> timekeeping.c:(.text+0x22ff4): undefined reference to `__udivdi3'
> kernel/built-in.o: In function `update_wall_time':
> (.text+0x23306): undefined reference to `__umoddi3'
> kernel/built-in.o: In function `update_wall_time':
> (.text+0x23326): undefined reference to `__udivdi3'
> kernel/built-in.o: In function `update_wall_time':
> (.text+0x23796): undefined reference to `__umoddi3'
> kernel/built-in.o: In function `update_wall_time':
> (.text+0x237b6): undefined reference to `__udivdi3'
From: himanshu.chauhan2@xxxxxxxxxxxx
To: kernelnewbies@xxxxxxxxxxxx
Subject: Query regarding 2.6.21.7 Compilation Patch
Date: Sun, 13 Dec 2009 09:11:01 +0000
2.6.21.7 is broken with latest GCC. The following patch fixes the issue. Its a build break because of compiler optimizing using modulo.
diff --git a/include/linux/time.h b/include/linux/time.h
index 2091a19..d32ef0a 100644
--- a/include/linux/time.h
+++ b/include/linux/time.h
@@ -174,6 +174,10 @@ 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++;
}
----------
My Question:
What is "asm ("" : "+r"(ns))" doing here and how does this fix the issue?
Thanks & Regards
Himanshu
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