| /* |
| * x86 FPU bug checks: |
| */ |
| #include <asm/fpu/internal.h> |
| |
| /* |
| * Boot time CPU/FPU FDIV bug detection code: |
| */ |
| |
| static double __initdata x = 4195835.0; |
| static double __initdata y = 3145727.0; |
| |
| /* |
| * This used to check for exceptions.. |
| * However, it turns out that to support that, |
| * the XMM trap handlers basically had to |
| * be buggy. So let's have a correct XMM trap |
| * handler, and forget about printing out |
| * some status at boot. |
| * |
| * We should really only care about bugs here |
| * anyway. Not features. |
| */ |
| void __init fpu__init_check_bugs(void) |
| { |
| u32 cr0_saved; |
| s32 fdiv_bug; |
| |
| /* kernel_fpu_begin/end() relies on patched alternative instructions. */ |
| if (!boot_cpu_has(X86_FEATURE_FPU)) |
| return; |
| |
| /* We might have CR0::TS set already, clear it: */ |
| cr0_saved = read_cr0(); |
| write_cr0(cr0_saved & ~X86_CR0_TS); |
| |
| kernel_fpu_begin(); |
| |
| /* |
| * trap_init() enabled FXSR and company _before_ testing for FP |
| * problems here. |
| * |
| * Test for the divl bug: http://en.wikipedia.org/wiki/Fdiv_bug |
| */ |
| __asm__("fninit\n\t" |
| "fldl %1\n\t" |
| "fdivl %2\n\t" |
| "fmull %2\n\t" |
| "fldl %1\n\t" |
| "fsubp %%st,%%st(1)\n\t" |
| "fistpl %0\n\t" |
| "fwait\n\t" |
| "fninit" |
| : "=m" (*&fdiv_bug) |
| : "m" (*&x), "m" (*&y)); |
| |
| kernel_fpu_end(); |
| |
| write_cr0(cr0_saved); |
| |
| if (fdiv_bug) { |
| set_cpu_bug(&boot_cpu_data, X86_BUG_FDIV); |
| pr_warn("Hmm, FPU with FDIV bug\n"); |
| } |
| } |