1 // SPDX-License-Identifier: GPL-2.0 2 /* 3 * x86 FPU bug checks: 4 */ 5 #include <linux/printk.h> 6 7 #include <asm/cpufeature.h> 8 #include <asm/fpu/api.h> 9 10 /* 11 * Boot time CPU/FPU FDIV bug detection code: 12 */ 13 14 static double __initdata x = 4195835.0; 15 static double __initdata y = 3145727.0; 16 17 /* 18 * This used to check for exceptions.. 19 * However, it turns out that to support that, 20 * the XMM trap handlers basically had to 21 * be buggy. So let's have a correct XMM trap 22 * handler, and forget about printing out 23 * some status at boot. 24 * 25 * We should really only care about bugs here 26 * anyway. Not features. 27 */ 28 void __init fpu__init_check_bugs(void) 29 { 30 s32 fdiv_bug; 31 32 /* kernel_fpu_begin/end() relies on patched alternative instructions. */ 33 if (!boot_cpu_has(X86_FEATURE_FPU)) 34 return; 35 36 kernel_fpu_begin(); 37 38 /* 39 * trap_init() enabled FXSR and company _before_ testing for FP 40 * problems here. 41 * 42 * Test for the divl bug: http://en.wikipedia.org/wiki/Fdiv_bug 43 */ 44 __asm__("fninit\n\t" 45 "fldl %1\n\t" 46 "fdivl %2\n\t" 47 "fmull %2\n\t" 48 "fldl %1\n\t" 49 "fsubp %%st,%%st(1)\n\t" 50 "fistpl %0\n\t" 51 "fwait\n\t" 52 "fninit" 53 : "=m" (*&fdiv_bug) 54 : "m" (*&x), "m" (*&y)); 55 56 kernel_fpu_end(); 57 58 if (fdiv_bug) { 59 set_cpu_bug(&boot_cpu_data, X86_BUG_FDIV); 60 pr_warn("Hmm, FPU with FDIV bug\n"); 61 } 62 } 63