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 static void __init check_fpu(void) 25 { 26 u32 cr0_saved; 27 s32 fdiv_bug; 28 29 /* We might have CR0::TS set already, clear it: */ 30 cr0_saved = read_cr0(); 31 write_cr0(cr0_saved & ~X86_CR0_TS); 32 33 kernel_fpu_begin(); 34 35 /* 36 * trap_init() enabled FXSR and company _before_ testing for FP 37 * problems here. 38 * 39 * Test for the divl bug: http://en.wikipedia.org/wiki/Fdiv_bug 40 */ 41 __asm__("fninit\n\t" 42 "fldl %1\n\t" 43 "fdivl %2\n\t" 44 "fmull %2\n\t" 45 "fldl %1\n\t" 46 "fsubp %%st,%%st(1)\n\t" 47 "fistpl %0\n\t" 48 "fwait\n\t" 49 "fninit" 50 : "=m" (*&fdiv_bug) 51 : "m" (*&x), "m" (*&y)); 52 53 kernel_fpu_end(); 54 55 write_cr0(cr0_saved); 56 57 if (fdiv_bug) { 58 set_cpu_bug(&boot_cpu_data, X86_BUG_FDIV); 59 pr_warn("Hmm, FPU with FDIV bug\n"); 60 } 61 } 62 63 void __init fpu__init_check_bugs(void) 64 { 65 /* 66 * kernel_fpu_begin/end() in check_fpu() relies on the patched 67 * alternative instructions. 68 */ 69 if (cpu_has_fpu) 70 check_fpu(); 71 } 72