Re: [PATCH] common implementation of iterative div/mod

[Andi Kleen <andi@firstfloor.org>]

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> It's:
> jeremy@cosworth:~/hg/xen/paravirt/linux-x86_64$ gcc -v
> Reading specs from /usr/lib/gcc/x86_64-linux/3.4.4/specs
> Configured with: ../src/configure -v
> --enable-languages=c,c++,java,f77,pascal,objc,ada,treelang --prefix=/usr
> --libexecdir=/usr/lib --with-gxx-include-dir=/usr/include/c++/3.4
> --enable-shared --with-system-zlib --enable-nls
> --without-included-gettext --program-suffix=-3.4 --enable-__cxa_atexit
> --enable-libstdcxx-allocator=mt --enable-clocale=gnu
> --enable-libstdcxx-debug --enable-java-gc=boehm --enable-java-awt=gtk
> --disable-werror x86_64-linux
> Thread model: posix
> gcc version 3.4.4 20050314 (prerelease) (Debian 3.4.3-13)
> 
> I think this is still a supported compiler, isn't it?

Yes. Here's a patch. You probably didn't see problems because you either
don't have a glibc that supports the vdso or none of your programs
gets the timezone from gettimeofday() [that is very obscure obsolete
functionality anyways, normally it should be gotten from the disk locales]

-Andi





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Use explicit copy in vdso_gettimeofday()

Jeremy's gcc 3.4 seems to be unable to inline a 8 byte memcpy. But
the vdso doesn't support external references. Copy the structure
members of struct timezone explicitely instead.

Signed-off-by: Andi Kleen <ak@linux.intel.com>

Index: linux/arch/x86/vdso/vclock_gettime.c
===================================================================
--- linux.orig/arch/x86/vdso/vclock_gettime.c
+++ linux/arch/x86/vdso/vclock_gettime.c
@@ -106,9 +106,9 @@ int __vdso_gettimeofday(struct timeval *
 		do_realtime((struct timespec *)tv);
 		tv->tv_usec /= 1000;
 		if (tz != NULL) {
-			/* This relies on gcc inlining the memcpy. We'll notice
-			   if it ever fails to do so. */
-			memcpy(tz, &gtod->sys_tz, sizeof(struct timezone));
+			/* Don't use memcpy. Some old compilers fail to inline it */
+			tz->tz_minuteswest = gtod->sys_tz.tz_minuteswest;
+			tz->tz_dsttime = gtod->sys_tz.tz_dsttime;
 		}
 		return 0;
 	}