Release 4.14 arch/x86/kernel/fpu/bugs.c

// SPDX-License-Identifier: GPL-2.0
/*
 * 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)
{
	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");
	}
}
Contributors
Person
Tokens
Prop
Commits
CommitProp
Ingo Molnar
37
77.08%
1
50.00%
Borislav Petkov
11
22.92%
1
50.00%
Total
48
100.00%
2
100.00%

Overall Contributors
Person
Tokens
Prop
Commits
CommitProp
Ingo Molnar
57
82.61%
1
33.33%
Borislav Petkov
11
15.94%
1
33.33%
Greg Kroah-Hartman
1
1.45%
1
33.33%
Total
69
100.00%
3
100.00%
Directory: arch/x86/kernel/fpu

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