1 // SPDX-License-Identifier: GPL-2.0 2 /* 3 * x86 FPU bug checks: 4 */ 5 #include <asm/fpu/internal.h> 6 7 /* 8 * Boot time CPU/FPU FDIV bug detection code: 9 */ 10 11 static double __initdata x = 4195835.0; 12 static double __initdata y = 3145727.0; 13 14 /* 15 * This used to check for exceptions.. 16 * However, it turns out that to support that, 17 * the XMM trap handlers basically had to 18 * be buggy. So let's have a correct XMM trap 19 * handler, and forget about printing out 20 * some status at boot. 21 * 22 * We should really only care about bugs here 23 * anyway. Not features. 24 */ 25 void __init fpu__init_check_bugs(void) 26 { 27 s32 fdiv_bug; 28 29 /* kernel_fpu_begin/end() relies on patched alternative instructions. */ 30 if (!boot_cpu_has(X86_FEATURE_FPU)) 31 return; 32 33 kernel_fpu_begin(); 34 35 /* 36 * trap_init() enabled FXSR and company _before_ testing for FP 37 * problems here. 38 * 39 * Test for the divl bug: http://en.wikipedia.org/wiki/Fdiv_bug 40 */ 41 __asm__("fninit\n\t" 42 "fldl %1\n\t" 43 "fdivl %2\n\t" 44 "fmull %2\n\t" 45 "fldl %1\n\t" 46 "fsubp %%st,%%st(1)\n\t" 47 "fistpl %0\n\t" 48 "fwait\n\t" 49 "fninit" 50 : "=m" (*&fdiv_bug) 51 : "m" (*&x), "m" (*&y)); 52 53 kernel_fpu_end(); 54 55 if (fdiv_bug) { 56 set_cpu_bug(&boot_cpu_data, X86_BUG_FDIV); 57 pr_warn("Hmm, FPU with FDIV bug\n"); 58 } 59 } 60