Hi Andreas, Replying to the list this time... On Tue, Sep 7, 2010 at 3:02 AM, Andreas Leppert <wudmx@xxxxxx> wrote: > Hello, > > I have encountered a problem on my 32 bit machine. Here some code > snippets: ...snip... > optimizer/built-in.o: In function `sys_optStopMeasure': > /source/trunk/linux-2.6.34/optimizer/sys_optStopMeasure.c:144: undefined > reference to `__divdi3' > > Another person which has tried the code had no problems - he compiled > the code for a 64 bit machine. Can you explain to me the problem? Why > does the code work on 64 but not on 32 bit? > > I've looked for some workarounds and found do_div(). Is this the way to > go? Or are there better ways? 32-bit kernels do not support 64-bit divides in the kernel. Using do_div is the correct way to do things. The reason it works in a 64-bit kernel is because a 64-bit CPU can do 64-bit divides. A 32-but CPU can only do 32-bit divides. You also have to consider that the linux kernel runs on more platforms that just x86. It also runs on ARM, MIPS, PowerPC, etc. The general rule is: there is no floating point support in kernel space (as a general rule: it may happen to work on some CPUs). Another general rule, is that on 32-bit CPUs you can only do 32-bit arithmetic, with 64-bit addition, subtraction, and multiplications. 64-bit divides must be done using do_div or do_div64. -- Dave Hylands Shuswap, BC, Canada http://www.DaveHylands.com/ -- To unsubscribe from this list: send an email with "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx Please read the FAQ at http://kernelnewbies.org/FAQ
