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/*
* x86 FPU bug checks:
*/
#include <asm/fpu/internal.h>
/*
* Boot time CPU/FPU FDIV bug detection code:
*/
static double __initdata x = 4195835.0;
static double __initdata y = 3145727.0;
/*
* This used to check for exceptions..
* However, it turns out that to support that,
* the XMM trap handlers basically had to
* be buggy. So let's have a correct XMM trap
* handler, and forget about printing out
* some status at boot.
*
* We should really only care about bugs here
* anyway. Not features.
*/
void __init fpu__init_check_bugs(void)
{
u32 cr0_saved;
s32 fdiv_bug;
/* kernel_fpu_begin/end() relies on patched alternative instructions. */
if (!boot_cpu_has(X86_FEATURE_FPU))
return;
/* We might have CR0::TS set already, clear it: */
cr0_saved = read_cr0();
write_cr0(cr0_saved & ~X86_CR0_TS);
kernel_fpu_begin();
/*
* trap_init() enabled FXSR and company _before_ testing for FP
* problems here.
*
* Test for the divl bug: http://en.wikipedia.org/wiki/Fdiv_bug
*/
__asm__("fninit\n\t"
"fldl %1\n\t"
"fdivl %2\n\t"
"fmull %2\n\t"
"fldl %1\n\t"
"fsubp %%st,%%st(1)\n\t"
"fistpl %0\n\t"
"fwait\n\t"
"fninit"
: "=m" (*&fdiv_bug)
: "m" (*&x), "m" (*&y));
kernel_fpu_end();
write_cr0(cr0_saved);
if (fdiv_bug) {
set_cpu_bug(&boot_cpu_data, X86_BUG_FDIV);
pr_warn("Hmm, FPU with FDIV bug\n");
}
}
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