On Fri, 18 May 2007 12:41:24 -0700
[email protected] wrote:
> http://bugzilla.kernel.org/show_bug.cgi?id=8501
Problem.
gcc-4.3 appears to have cunningly converted this:
static inline void timespec_add_ns(struct timespec *a, u64 ns)
{
ns += a->tv_nsec;
while(unlikely(ns >= NSEC_PER_SEC)) {
ns -= NSEC_PER_SEC;
a->tv_sec++;
}
a->tv_nsec = ns;
}
into a divide-by-1000000000 operation, so it emits a call to udivdi3 and we
don't link.
I expect that this optimisation will remain in gcc-4.3 and we'll end up
having major kernel releases which don't build on i386 with major gcc
releases, which isn't altogether desirable. I suspect we'll need to fix this
fairly urgently, and to backport the fix into a number of kernel releases.
We use the above idiom in several places. A suitable fix might be to hunt
down those various sites and then make them call a helper function which
does
if (unlikely(ns >= NSEC_PER_SEC)) {
do_div(...)
}
(Better would be to inline the comparison and to uninline the do_div(),
if it's a 32-bit arch. Doing all this in a backportable fashion may
prove tricky)
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