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1 Target Definitions for R8C/M16C/M32C
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2 Copyright (C) 2005-2018 Free Software Foundation, Inc.
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3 Contributed by Red Hat.
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4
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5 This file is part of GCC.
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6
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7 GCC is free software; you can redistribute it and/or modify it
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8 under the terms of the GNU General Public License as published
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9 by the Free Software Foundation; either version 3, or (at your
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10 option) any later version.
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11
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12 GCC is distributed in the hope that it will be useful, but WITHOUT
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13 ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
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14 or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public
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15 License for more details.
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16
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17 You should have received a copy of the GNU General Public License
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18 along with GCC; see the file COPYING3. If not see
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19 <http://www.gnu.org/licenses/>.
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20
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21
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22 These are just some random notes I used during development of this
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23 port. Please don't consider these to be "official" specifications,
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24 just additional information to help make the code easier to
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25 understand.
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26
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27
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28 Frame
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29 =====
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30
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31 +--------------------
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32 | incoming args
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33 +--------------------
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34 | return Address
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35 osp -> +--------------------
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36 | saved fp
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37 fp -> +--------------------
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38 | local data
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39 +--------------------
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40 | saved regs
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41 +--------------------
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42 | outgoing args (opt)
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43 sp -> +--------------------
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44
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45 Argument Passing
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46 ================
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47
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48 r8c, m16c
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49 ---------
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50
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51 First arg may be passed in r1l or r1 if it (1) fits (QImode or
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52 HImode), (2) is named, and (3) is an integer or pointer type (no
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53 structs, floats, etc). Otherwise, it's passed on the stack.
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54
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55 Second arg may be passed in r2, same restrictions (but not QImode),
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56 even if the first arg is passed on the stack.
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57
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58 Third and further args are passed on the stack. No padding is used,
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59 stack "alignment" is 8 bits.
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60
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61 m32cm, m32c
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62 -----------
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63 First arg may be passed in r0l or r0, same restrictions as above.
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64
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65 Second and further args are passed on the stack. Padding is used
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66 after QImode parameters (i.e. lower-addressed byte is the value,
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67 higher-addressed byte is the padding), stack "alignment" is 16 bits.
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68
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69
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70 Return Value
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71 ============
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72
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73 r8c, m16c
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74 ---------
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75
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76 QImode in r0l
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77 HImode in r0
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78 near pointer in r0
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79 (desired)
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80 SImode in r2r0
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81 far pointer in r2r0
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82 (actual)
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83 Anything bigger than 16 bits is returned in memory, at mem0 (mem0
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84 through mem15 are provided by libgcc.a)
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85
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86 Aggregate values (regardless of size) are returned by pushing a
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87 pointer to a temporary area on the stack after the args are pushed.
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88 The function fills in this area with the value. Note that this
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89 pointer on the stack does not affect how register arguments, if any,
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90 are configured.
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91
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92 m32cm, m32c
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93 -----------
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94 Same.
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95
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96
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97 Registers Preserved Across Calls
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98 ================================
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99
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100 r8c, m16c
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101 ---------
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102 sb, fb, sp (i.e. nearly all registers are call clobbered)
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103
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104 m32cm, m32c
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105 -----------
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106 r1, r2, r3, a0, a1, sb, fb, sp
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107 (except when used for return values)
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108
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109
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110 Interrupt Handlers
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111 ==================
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112
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113 The stack frame is slightly different for interrupt handlers, because
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114 (1) we don't have a usable parent frame, and (2) we have to use
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115 special instructions to return and thus must save/restore everything
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116 differently.
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117
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118 +--------------------
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119 | program state
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120 osp -> +--------------------
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121 | return address
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122 +--------------------
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123 | saved r0..fp (pushm)
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124 fp -> +--------------------
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125 | local data
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126 +--------------------
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127 | saved regs mem0..mem15
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128 +--------------------
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129 | outgoing args (opt)
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130 sp -> +--------------------
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131
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