lldb/source/Plugins/Process/Utility/RegisterContext_x86.cpp

   1 //===-- RegisterContext_x86.cpp ---------------------------------*- C++ -*-===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #include "RegisterContext_x86.h"
  10
  11 using namespace lldb_private;
  12
  13 // Convert the 8-bit abridged FPU Tag Word (as found in FXSAVE) to the full
  14 // 16-bit FPU Tag Word (as found in FSAVE, and used by gdb protocol).  This
  15 // requires knowing the values of the ST(i) registers and the FPU Status Word.
  16 uint16_t lldb_private::AbridgedToFullTagWord(uint8_t abridged_tw, uint16_t sw,
  17                                              llvm::ArrayRef<MMSReg> st_regs) {
  18   // Tag word is using internal FPU register numbering rather than ST(i).
  19   // Mapping to ST(i): i = FPU regno - TOP (Status Word, bits 11:13).
  20   // Here we start with FPU reg 7 and go down.
  21   int st = 7 - ((sw >> 11) & 7);
  22   uint16_t tw = 0;
  23   for (uint8_t mask = 0x80; mask != 0; mask >>= 1) {
  24     tw <<= 2;
  25     if (abridged_tw & mask) {
  26       // The register is non-empty, so we need to check the value of ST(i).
  27       uint16_t exp =
  28           st_regs[st].comp.sign_exp & 0x7fff; // Discard the sign bit.
  29       if (exp == 0) {
  30         if (st_regs[st].comp.mantissa == 0)
  31           tw |= 1; // Zero
  32         else
  33           tw |= 2; // Denormal
  34       } else if (exp == 0x7fff)
  35         tw |= 2; // Infinity or NaN
  36       // 0 if normal number
  37     } else
  38       tw |= 3; // Empty register
  39
  40     // Rotate ST down.
  41     st = (st - 1) & 7;
  42   }
  43
  44   return tw;
  45 }
  46
  47 // Convert the 16-bit FPU Tag Word to the abridged 8-bit value, to be written
  48 // into FXSAVE.
  49 uint8_t lldb_private::FullToAbridgedTagWord(uint16_t tw) {
  50   uint8_t abridged_tw = 0;
  51   for (uint16_t mask = 0xc000; mask != 0; mask >>= 2) {
  52     abridged_tw <<= 1;
  53     // full TW uses 11 for empty registers, aTW uses 0
  54     if ((tw & mask) != mask)
  55       abridged_tw |= 1;
  56   }
  57   return abridged_tw;
  58 }