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 u32 cr0_saved; 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 /* We might have CR0::TS set already, clear it: */ 34 cr0_saved = read_cr0(); 35 write_cr0(cr0_saved & ~X86_CR0_TS); 36 37 kernel_fpu_begin(); 38 39 /* 40 * trap_init() enabled FXSR and company _before_ testing for FP 41 * problems here. 42 * 43 * Test for the divl bug: http://en.wikipedia.org/wiki/Fdiv_bug 44 */ 45 __asm__("fninit\n\t" 46 "fldl %1\n\t" 47 "fdivl %2\n\t" 48 "fmull %2\n\t" 49 "fldl %1\n\t" 50 "fsubp %%st,%%st(1)\n\t" 51 "fistpl %0\n\t" 52 "fwait\n\t" 53 "fninit" 54 : "=m" (*&fdiv_bug) 55 : "m" (*&x), "m" (*&y)); 56 57 kernel_fpu_end(); 58 59 write_cr0(cr0_saved); 60 61 if (fdiv_bug) { 62 set_cpu_bug(&boot_cpu_data, X86_BUG_FDIV); 63 pr_warn("Hmm, FPU with FDIV bug\n"); 64 } 65 } 66