| 1 | //===-- RegisterContext_x86.cpp ---------------------------------*- C++ -*-===// |
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| 2 | // |
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| 3 | // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
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| 4 | // See https://llvm.org/LICENSE.txt for license information. |
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| 5 | // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
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| 6 | // |
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| 7 | //===----------------------------------------------------------------------===// |
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| 8 | |
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| 9 | #include "RegisterContext_x86.h" |
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| 10 | |
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| 11 | using namespace lldb_private; |
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| 12 | |
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| 13 | // Convert the 8-bit abridged FPU Tag Word (as found in FXSAVE) to the full |
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| 14 | // 16-bit FPU Tag Word (as found in FSAVE, and used by gdb protocol). This |
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| 15 | // requires knowing the values of the ST(i) registers and the FPU Status Word. |
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| 16 | uint16_t lldb_private::AbridgedToFullTagWord(uint8_t abridged_tw, uint16_t sw, |
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| 17 | llvm::ArrayRef<MMSReg> st_regs) { |
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| 18 | // Tag word is using internal FPU register numbering rather than ST(i). |
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| 19 | // Mapping to ST(i): i = FPU regno - TOP (Status Word, bits 11:13). |
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| 20 | // Here we start with FPU reg 7 and go down. |
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| 21 | int st = 7 - ((sw >> 11) & 7); |
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| 22 | uint16_t tw = 0; |
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| 23 | for (uint8_t mask = 0x80; mask != 0; mask >>= 1) { |
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| 24 | tw <<= 2; |
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| 25 | if (abridged_tw & mask) { |
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| 26 | // The register is non-empty, so we need to check the value of ST(i). |
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| 27 | uint16_t exp = |
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| 28 | st_regs[st].comp.sign_exp & 0x7fff; // Discard the sign bit. |
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| 29 | if (exp == 0) { |
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| 30 | if (st_regs[st].comp.mantissa == 0) |
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| 31 | tw |= 1; // Zero |
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| 32 | else |
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| 33 | tw |= 2; // Denormal |
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| 34 | } else if (exp == 0x7fff) |
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| 35 | tw |= 2; // Infinity or NaN |
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| 36 | // 0 if normal number |
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| 37 | } else |
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| 38 | tw |= 3; // Empty register |
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| 39 | |
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| 40 | // Rotate ST down. |
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| 41 | st = (st - 1) & 7; |
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| 42 | } |
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| 43 | |
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| 44 | return tw; |
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| 45 | } |
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| 46 | |
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| 47 | // Convert the 16-bit FPU Tag Word to the abridged 8-bit value, to be written |
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| 48 | // into FXSAVE. |
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| 49 | uint8_t lldb_private::FullToAbridgedTagWord(uint16_t tw) { |
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| 50 | uint8_t abridged_tw = 0; |
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| 51 | for (uint16_t mask = 0xc000; mask != 0; mask >>= 2) { |
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| 52 | abridged_tw <<= 1; |
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| 53 | // full TW uses 11 for empty registers, aTW uses 0 |
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| 54 | if ((tw & mask) != mask) |
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| 55 | abridged_tw |= 1; |
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| 56 | } |
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| 57 | return abridged_tw; |
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| 58 | } |
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| 59 | |
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