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1 Target Definitions for R8C/M16C/M32C
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2 Copyright (C) 2005, 2007
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3 Free Software Foundation, Inc.
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4 Contributed by Red Hat.
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5
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6 This file is part of GCC.
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7
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8 GCC is free software; you can redistribute it and/or modify it
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9 under the terms of the GNU General Public License as published
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10 by the Free Software Foundation; either version 3, or (at your
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11 option) any later version.
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12
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13 GCC is distributed in the hope that it will be useful, but WITHOUT
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14 ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
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15 or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public
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16 License for more details.
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17
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18 You should have received a copy of the GNU General Public License
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19 along with GCC; see the file COPYING3. If not see
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20 <http://www.gnu.org/licenses/>.
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21
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22
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23 These are just some random notes I used during development of this
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24 port. Please don't consider these to be "official" specifications,
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25 just additional information to help make the code easier to
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26 understand.
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27
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28
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29 Frame
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30 =====
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31
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32 +--------------------
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33 | incoming args
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34 +--------------------
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35 | return Address
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36 osp -> +--------------------
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37 | saved fp
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38 fp -> +--------------------
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39 | local data
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40 +--------------------
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41 | saved regs
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42 +--------------------
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43 | outgoing args (opt)
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44 sp -> +--------------------
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45
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46 Argument Passing
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47 ================
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48
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49 r8c, m16c
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50 ---------
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51
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52 First arg may be passed in r1l or r1 if it (1) fits (QImode or
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53 HImode), (2) is named, and (3) is an integer or pointer type (no
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54 structs, floats, etc). Otherwise, it's passed on the stack.
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55
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56 Second arg may be passed in r2, same restrictions (but not QImode),
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57 even if the first arg is passed on the stack.
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58
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59 Third and further args are passed on the stack. No padding is used,
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60 stack "alignment" is 8 bits.
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61
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62 m32cm, m32c
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63 -----------
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64 First arg may be passed in r0l or r0, same restrictions as above.
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65
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66 Second and further args are passed on the stack. Padding is used
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67 after QImode parameters (i.e. lower-addressed byte is the value,
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68 higher-addressed byte is the padding), stack "alignment" is 16 bits.
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69
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70
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71 Return Value
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72 ============
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73
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74 r8c, m16c
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75 ---------
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76
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77 QImode in r0l
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78 HImode in r0
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79 near pointer in r0
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80 (desired)
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81 SImode in r2r0
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82 far pointer in r2r0
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83 (actual)
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84 Anything bigger than 16 bits is returned in memory, at mem0 (mem0
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85 through mem15 are provided by libgcc.a)
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86
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87 Aggregate values (regardless of size) are returned by pushing a
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88 pointer to a temporary area on the stack after the args are pushed.
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89 The function fills in this area with the value. Note that this
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90 pointer on the stack does not affect how register arguments, if any,
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91 are configured.
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92
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93 m32cm, m32c
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94 -----------
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95 Same.
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96
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97
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98 Registers Preserved Across Calls
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99 ================================
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100
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101 r8c, m16c
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102 ---------
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103 sb, fb, sp (i.e. nearly all registers are call clobbered)
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104
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105 m32cm, m32c
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106 -----------
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107 r1, r2, r3, a0, a1, sb, fb, sp
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108 (except when used for return values)
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109
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110
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111 Interrupt Handlers
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112 ==================
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113
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114 The stack frame is slightly different for interrupt handlers, because
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115 (1) we don't have a usable parent frame, and (2) we have to use
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116 special instructions to return and thus must save/restore everything
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117 differently.
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118
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119 +--------------------
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120 | program state
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121 osp -> +--------------------
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122 | return address
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123 +--------------------
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124 | saved r0..fp (pushm)
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125 fp -> +--------------------
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126 | local data
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127 +--------------------
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128 | saved regs mem0..mem15
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129 +--------------------
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130 | outgoing args (opt)
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131 sp -> +--------------------
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132
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