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 | } |
59 | |