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71 lines
1.4 KiB
71 lines
1.4 KiB
/* |
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* x86 FPU bug checks: |
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*/ |
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#include <asm/fpu/internal.h> |
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/* |
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* Boot time CPU/FPU FDIV bug detection code: |
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*/ |
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static double __initdata x = 4195835.0; |
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static double __initdata y = 3145727.0; |
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/* |
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* This used to check for exceptions.. |
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* However, it turns out that to support that, |
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* the XMM trap handlers basically had to |
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* be buggy. So let's have a correct XMM trap |
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* handler, and forget about printing out |
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* some status at boot. |
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* |
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* We should really only care about bugs here |
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* anyway. Not features. |
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*/ |
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static void __init check_fpu(void) |
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{ |
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u32 cr0_saved; |
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s32 fdiv_bug; |
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/* We might have CR0::TS set already, clear it: */ |
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cr0_saved = read_cr0(); |
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write_cr0(cr0_saved & ~X86_CR0_TS); |
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kernel_fpu_begin(); |
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/* |
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* trap_init() enabled FXSR and company _before_ testing for FP |
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* problems here. |
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* |
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* Test for the divl bug: http://en.wikipedia.org/wiki/Fdiv_bug |
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*/ |
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__asm__("fninit\n\t" |
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"fldl %1\n\t" |
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"fdivl %2\n\t" |
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"fmull %2\n\t" |
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"fldl %1\n\t" |
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"fsubp %%st,%%st(1)\n\t" |
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"fistpl %0\n\t" |
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"fwait\n\t" |
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"fninit" |
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: "=m" (*&fdiv_bug) |
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: "m" (*&x), "m" (*&y)); |
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kernel_fpu_end(); |
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write_cr0(cr0_saved); |
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if (fdiv_bug) { |
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set_cpu_bug(&boot_cpu_data, X86_BUG_FDIV); |
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pr_warn("Hmm, FPU with FDIV bug\n"); |
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} |
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} |
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void __init fpu__init_check_bugs(void) |
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{ |
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/* |
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* kernel_fpu_begin/end() in check_fpu() relies on the patched |
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* alternative instructions. |
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*/ |
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if (cpu_has_fpu) |
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check_fpu(); |
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}
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