// SPDX-License-Identifier: GPL-2.0
/*
 * x86 FPU bug checks:
 */
#include <linux/printk.h>

#include <asm/cpufeature.h>
#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");
        }
}