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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
10
11using 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.
16uint16_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.
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}
A class that represents a running process on the host machine.
Definition: SBAttachInfo.h:14
uint16_t AbridgedToFullTagWord(uint8_t abridged_tw, uint16_t sw, llvm::ArrayRef< MMSReg > st_regs)
uint8_t FullToAbridgedTagWord(uint16_t tw)