60 lines
1.2 KiB
C
60 lines
1.2 KiB
C
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// SPDX-License-Identifier: GPL-2.0
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/*
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* x86 FPU bug checks:
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*/
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#include <asm/fpu/api.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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void __init fpu__init_check_bugs(void)
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{
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s32 fdiv_bug;
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/* kernel_fpu_begin/end() relies on patched alternative instructions. */
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if (!boot_cpu_has(X86_FEATURE_FPU))
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return;
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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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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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