Messages in this thread | | | Date | Mon, 2 Oct 2006 19:34:27 -0700 (PDT) | From | Linus Torvalds <> | Subject | Re: [PATCH/RFC] Math-emu kills the kernel on Athlon64 X2 |
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On Mon, 2 Oct 2006, Randy Dunlap wrote: > > I had no trouble reproducing the boot failure (on Pentium-M), then > I tried TRACE_RESUME(). Nifty, but not really needed here since > earlyprintk worked and contained the fault messages: > > [ 16.841784] math_emulate: 0060:c01062dd > [ 16.845579] Kernel panic - not syncing: Math emulation needed in kernel > > But CONFIG_MATH_EMULATION=y, so what now?
The "Math emulation needed in kernel" message means that it was asked to emulate a kernel instruction, and it refuses to do so. The emulation is _not_ meant to be a real FPU, it simply looks like one to user space. A lot of things aren't really emulated (there's no global x87 context, for example: the context is all strictly per-process).
> Linus mentioned CPU feature bits. The message log above didn't > make me feel good about them. Sure enough, we are playing with > features before reading the feature bits.
Please look up address c01062dd in the system map (or just using gdb), that will tell you what code _tried_ to use the math coprocessor in kernel space.
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