Line data    Source code

       1             : // SPDX-License-Identifier: GPL-2.0
       2             : /*
       3             :  * x86 FPU bug checks:
       4             :  */
       5             : #include <asm/fpu/internal.h>
       6             : 
       7             : /*
       8             :  * Boot time CPU/FPU FDIV bug detection code:
       9             :  */
      10             : 
      11             : static double __initdata x = 4195835.0;
      12             : static double __initdata y = 3145727.0;
      13             : 
      14             : /*
      15             :  * This used to check for exceptions..
      16             :  * However, it turns out that to support that,
      17             :  * the XMM trap handlers basically had to
      18             :  * be buggy. So let's have a correct XMM trap
      19             :  * handler, and forget about printing out
      20             :  * some status at boot.
      21             :  *
      22             :  * We should really only care about bugs here
      23             :  * anyway. Not features.
      24             :  */
      25           0 : void __init fpu__init_check_bugs(void)
      26             : {
      27           0 :         s32 fdiv_bug;
      28             : 
      29             :         /* kernel_fpu_begin/end() relies on patched alternative instructions. */
      30           0 :         if (!boot_cpu_has(X86_FEATURE_FPU))
      31             :                 return;
      32             : 
      33           0 :         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           0 :         __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           0 :         kernel_fpu_end();
      54             : 
      55           0 :         if (fdiv_bug) {
      56           0 :                 set_cpu_bug(&boot_cpu_data, X86_BUG_FDIV);
      57           0 :                 pr_warn("Hmm, FPU with FDIV bug\n");
      58             :         }
      59             : }