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- // SPDX-License-Identifier: GPL-2.0
- /*
- * x86 FPU bug checks:
- */
- #include <asm/fpu/api.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)
- {
- s32 fdiv_bug;
- /* kernel_fpu_begin/end() relies on patched alternative instructions. */
- if (!boot_cpu_has(X86_FEATURE_FPU))
- return;
- 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();
- if (fdiv_bug) {
- set_cpu_bug(&boot_cpu_data, X86_BUG_FDIV);
- pr_warn("Hmm, FPU with FDIV bug\n");
- }
- }
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