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 */ fpu__init_check_bugs(void)28void __init fpu__init_check_bugs(void) 29 { 30 s32 fdiv_bug; 31 32 kernel_fpu_begin(); 33 34 /* 35 * trap_init() enabled FXSR and company _before_ testing for FP 36 * problems here. 37 * 38 * Test for the divl bug: http://en.wikipedia.org/wiki/Fdiv_bug 39 */ 40 __asm__("fninit\n\t" 41 "fldl %1\n\t" 42 "fdivl %2\n\t" 43 "fmull %2\n\t" 44 "fldl %1\n\t" 45 "fsubp %%st,%%st(1)\n\t" 46 "fistpl %0\n\t" 47 "fwait\n\t" 48 "fninit" 49 : "=m" (*&fdiv_bug) 50 : "m" (*&x), "m" (*&y)); 51 52 kernel_fpu_end(); 53 54 if (fdiv_bug) { 55 set_cpu_bug(&boot_cpu_data, X86_BUG_FDIV); 56 pr_warn("Hmm, FPU with FDIV bug\n"); 57 } 58 } 59