// 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"); } }