1 /* 2 * x86 FPU bug checks: 3 */ 4 #include <asm/fpu/internal.h> 5 6 /* 7 * Boot time CPU/FPU FDIV bug detection code: 8 */ 9 10 static double __initdata x = 4195835.0; 11 static double __initdata y = 3145727.0; 12 13 /* 14 * This used to check for exceptions.. 15 * However, it turns out that to support that, 16 * the XMM trap handlers basically had to 17 * be buggy. So let's have a correct XMM trap 18 * handler, and forget about printing out 19 * some status at boot. 20 * 21 * We should really only care about bugs here 22 * anyway. Not features. 23 */ 24 void __init fpu__init_check_bugs(void) 25 { 26 s32 fdiv_bug; 27 28 /* kernel_fpu_begin/end() relies on patched alternative instructions. */ 29 if (!boot_cpu_has(X86_FEATURE_FPU)) 30 return; 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