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1 <chapter>
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2 <title>Characteristics of Compiled Programs</title>
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3
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4 <section>
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5 <title>The Object Code Module</title>
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6 <para>
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468
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7 The compiler produces position-independent, reentrant 6809 code
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8 in a standard OS-9 memory module format. The format of an executable
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9 program module is shown below. Detailed descriptions of each
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10 section of the module are given on following pages.
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466
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11 </para>
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468
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12 <informalfigure>
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13 <screen>
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14 Module
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15 Offset
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16
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17 +-------------------------------+
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18 ! !
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19 ! Module Header !
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20 ! !
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21 !-------------------------------!
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22 ! Execution Offset !
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23 !-------------------------------!
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24 ! Permanent Storage Size !
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25 !-------------------------------!
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26 ! Data-text Reference Count !
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27 v v
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28 : Data-text Reference Offsets :
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29 ^ ^
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30 </screen>
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31 </informalfigure>
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466
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32 <section>
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468
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33 <title>Module Header</title>
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34 <para>
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35 This is a standard module header with the type/language byte set to
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36 $11 (Program + 6809 Object Code), and the attribute/revision byte
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37 set to $81 (Reentrant + 1).
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38 </para>
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39 </section>
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40
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41 <section>
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42 <title>Execution Offset</title>
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43 <para>
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44 </para>
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45 </section>
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46
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47 <section>
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48 <title>Storage Size</title>
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49 <para>
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50 </para>
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51 </section>
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52
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53 <section>
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54 <title>Module Name</title>
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55 <para>
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56 </para>
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57 </section>
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58
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59 <section>
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60 <title>Information</title>
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61 <para>
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62 </para>
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63 </section>
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64
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65 <section>
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66 <title>Executable Code</title>
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67 <para>
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68 </para>
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69 </section>
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70
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71 <section>
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72 <title>String Literals</title>
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73 <para>
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74 </para>
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75 </section>
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76
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77 <section>
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78 <title>Initializing Data and its Size</title>
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79 <para>
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80 </para>
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81 </section>
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82
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83 <section>
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84 <title>Data References</title>
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85 <para>
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86 </para>
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87 </section>
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88 </section>
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89
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90 <section>
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91 <title>Memory Management</title>
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92 <para>
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93 The C compiler and its support programs have default conditions
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94 such that the average programmer need not be concerned with details
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95 of memory management. However, there are situations where advanced
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96 programmers may wish to tailor the storage allocation of a program
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97 for special situations. The following information explains in
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98 detail how a C program's data area is allocated and used.
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99 </para>
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100
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101 <section>
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102 <title>Typical C Program Memory Map</title>
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103 <para>
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104 </para>
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105 </section>
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106
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107 <section>
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108 <title>Compile Time Memory Allocation</title>
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109 <para>
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110 </para>
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565
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111 <para>
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112 The following rules can serve as a rough guide to estimate how
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113 much memory to specify:
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114 </para>
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115 <orderedlist>
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116 <listitem><para>
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117 The parameter area should be large enough for any anticipated
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118 command line string.
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119 </para></listitem>
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120 <listitem><para>
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121 The stack should not be less than 128 bytes and should take
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122 into account the depth of function calling chains and any
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123 recursion.
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124 </para></listitem>
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125 <listitem><para>
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126 All function arguments and local variables occupy stack space
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127 and each function entered needs 4 bytes more for the return
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128 address and temporary storage of the calling function's register
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129 variable.
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130 </para></listitem>
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131 <listitem><para>
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132 Free memory is requested by the Standard Library I/O
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133 functions for buffers at the rate of 256 bytes per accessed
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134 file. The does not apply to the lower level service request I/O
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135 functions such as "open()", "read()" or "write()" not to
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136 "stderr" which is always un-buffered, but it does apply to both
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137 "stdin" and "stdout" (see the Standard Library documentation).
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138 </para></listitem>
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139 </orderedlist>
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140 <para>
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141 A good method for getting a feel for how much memory is
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142 needed by your program is to allow the linker to set the memory size
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143 to its usually conservative value. Then, if the program runs
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144 with a variety of input satisfactorily but memory is limited on the
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145 system, try reducing the allocation at the next compilation. If a
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146 stack overflow occurs or an "ibrk()" call returns -1, then try
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147 increasing the memory next time. You cannot damage the system by
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148 getting it wrong, but data may be lost if the program runs out of
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149 space at a crucial time. It pays to be in error on the generous
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150 side.
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151 </para>
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530
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152 </section>
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468
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153 </section>
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466
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154 </chapter>
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