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RegisterContext_x86.cpp
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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.
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.
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 }
lldb_private::AbridgedToFullTagWord
uint16_t AbridgedToFullTagWord(uint8_t abridged_tw, uint16_t sw, llvm::ArrayRef< MMSReg > st_regs)
Definition: RegisterContext_x86.cpp:16
lldb_private::FullToAbridgedTagWord
uint8_t FullToAbridgedTagWord(uint16_t tw)
Definition: RegisterContext_x86.cpp:49
uint16_t
RegisterContext_x86.h
lldb_private
A class that represents a running process on the host machine.
Definition: SBCommandInterpreterRunOptions.h:16