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