scoutos / prex-0.9.0 / bsp / hal / x86 / arch / context.c @ 03e9c04a
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1 | 03e9c04a | Brad Neuman | /*-
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2 | * Copyright (c) 2005-2009, Kohsuke Ohtani
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3 | * All rights reserved.
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4 | *
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5 | * Redistribution and use in source and binary forms, with or without
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6 | * modification, are permitted provided that the following conditions
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7 | * are met:
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8 | * 1. Redistributions of source code must retain the above copyright
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9 | * notice, this list of conditions and the following disclaimer.
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10 | * 2. Redistributions in binary form must reproduce the above copyright
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11 | * notice, this list of conditions and the following disclaimer in the
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12 | * documentation and/or other materials provided with the distribution.
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13 | * 3. Neither the name of the author nor the names of any co-contributors
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14 | * may be used to endorse or promote products derived from this software
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15 | * without specific prior written permission.
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16 | *
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17 | * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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18 | * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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19 | * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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20 | * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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21 | * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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22 | * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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23 | * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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24 | * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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25 | * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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26 | * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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27 | * SUCH DAMAGE.
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28 | */
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29 | |||
30 | /*
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31 | * context.c - context management routines
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32 | */
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33 | |||
34 | /*
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35 | * The context consists of kernel/user mode registers, and kernel
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36 | * stack. The user mode registers are always saved to the kernel
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37 | * stack when processor enters kernel mode by H/W or S/W events.
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38 | *
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39 | * The user mode registers are located in the interrupt/trap
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40 | * frame at the top of the kernel stack. Before the control
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41 | * returns to user mode next time, these register value will be
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42 | * restored automatically.
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43 | *
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44 | * All thread owns its context to keep its execution state. The
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45 | * scheduler will switch the context to change an active thread.
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46 | */
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47 | |||
48 | #include <kernel.h> |
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49 | #include <kmem.h> |
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50 | #include <cpu.h> |
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51 | #include <trap.h> |
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52 | #include <context.h> |
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53 | #include <locore.h> |
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54 | |||
55 | /*
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56 | * Set user mode registers into the specific context.
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57 | *
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58 | * Note: When user mode program counter is set, all register
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59 | * values except a stack pointer are reset to default value.
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60 | */
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61 | void
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62 | context_set(context_t ctx, int type, register_t val)
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63 | { |
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64 | struct kern_regs *k;
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65 | struct cpu_regs *u;
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66 | uint32_t *argp; |
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67 | |||
68 | k = &ctx->kregs; |
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69 | |||
70 | switch (type) {
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71 | case CTX_KSTACK:
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72 | /* Set kernel mode stack pointer */
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73 | ctx->uregs = (struct cpu_regs *)
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74 | ((uint32_t)val - sizeof(struct cpu_regs)); |
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75 | ctx->esp0 = (uint32_t)val; |
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76 | |||
77 | k->eip = (uint32_t)&syscall_ret; |
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78 | k->esp = (uint32_t)ctx->uregs - sizeof(uint32_t);
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79 | |||
80 | /* Reset minimum user mode registers */
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81 | u = ctx->uregs; |
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82 | u->eax = 0;
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83 | u->eflags = (uint32_t)(EFL_IF | EFL_IOPL_KERN); |
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84 | break;
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85 | |||
86 | case CTX_KENTRY:
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87 | /* Kernel mode program counter */
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88 | k->eip = (uint32_t)val; |
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89 | break;
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90 | |||
91 | case CTX_KARG:
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92 | /* Kernel mode argument */
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93 | argp = (uint32_t *)(k->esp + sizeof(uint32_t) * 2); |
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94 | *argp = (uint32_t)val; |
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95 | break;
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96 | |||
97 | case CTX_USTACK:
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98 | /* User mode stack pointer */
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99 | u = ctx->uregs; |
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100 | u->esp = (uint32_t)val; |
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101 | u->ss = (uint32_t)(USER_DS | 3); /* fail safe */ |
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102 | break;
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103 | |||
104 | case CTX_UENTRY:
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105 | /* User mode program counter */
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106 | u = ctx->uregs; |
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107 | u->eip = (uint32_t)val; |
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108 | u->cs = (uint32_t)(USER_CS | 3);
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109 | u->ds = u->es = (uint32_t)(USER_DS | 3);
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110 | u->eflags = (uint32_t)(EFL_IF | EFL_IOPL_KERN); |
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111 | u->eax = u->ebx = u->ecx = u->edx = |
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112 | u->edi = u->esi = u->ebp = 0;
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113 | break;
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114 | |||
115 | case CTX_UARG:
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116 | /* User mode argument */
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117 | u = ctx->uregs; |
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118 | argp = (uint32_t *)(u->esp + sizeof(uint32_t));
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119 | copyout(&val, argp, sizeof(uint32_t));
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120 | break;
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121 | |||
122 | default:
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123 | /* invalid */
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124 | break;
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125 | } |
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126 | } |
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127 | |||
128 | /*
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129 | * Switch to new context
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130 | *
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131 | * Kernel mode registers and kernel stack pointer are switched to
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132 | * the next context.
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133 | *
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134 | * We don't use x86 task switch mechanism to minimize the context
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135 | * space. The system has only one TSS(task state segment), and
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136 | * the context switching is done by changing the register value
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137 | * in this TSS. Processor will reload them automatically when it
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138 | * enters to the kernel mode in next time.
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139 | *
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140 | * It is assumed all interrupts are disabled by caller.
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141 | *
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142 | * TODO: FPU context is not switched as of now.
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143 | */
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144 | void
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145 | context_switch(context_t prev, context_t next) |
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146 | { |
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147 | /* Set kernel stack pointer in TSS (esp0). */
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148 | tss_set((uint32_t)next->esp0); |
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149 | |||
150 | /* Save the previous context, and restore the next context */
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151 | cpu_switch(&prev->kregs, &next->kregs); |
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152 | } |
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153 | |||
154 | /*
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155 | * Save user mode context to handle exceptions.
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156 | *
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157 | * Copy current user mode registers in the kernel stack to the
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158 | * user mode stack. The user stack pointer is adjusted for this
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159 | * area. So that the exception handler can get the register
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160 | * state of the target thread.
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161 | *
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162 | * It builds arguments for the exception handler in the following
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163 | * format.
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164 | *
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165 | * void exception_handler(int exc, void *regs);
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166 | */
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167 | void
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168 | context_save(context_t ctx) |
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169 | { |
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170 | struct cpu_regs *cur, *sav;
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171 | |||
172 | /* Copy current register context into user mode stack */
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173 | cur = ctx->uregs; |
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174 | sav = (struct cpu_regs *)(cur->esp - sizeof(*sav)); |
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175 | copyout(cur, sav, sizeof(*sav));
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176 | |||
177 | |||
178 | ctx->saved_regs = sav; |
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179 | |||
180 | /* Adjust stack pointer */
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181 | cur->esp = (uint32_t)sav - (sizeof(uint32_t) * 2); |
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182 | } |
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183 | |||
184 | /*
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185 | * Restore register context to return from the exception handler.
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186 | */
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187 | void
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188 | context_restore(context_t ctx) |
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189 | { |
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190 | struct cpu_regs *cur;
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191 | |||
192 | /* Restore user mode context */
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193 | cur = ctx->uregs; |
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194 | copyin(ctx->saved_regs, cur, sizeof(*cur));
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195 | |||
196 | /* Correct some registers for fail safe */
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197 | cur->cs = (uint32_t)(USER_CS | 3);
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198 | cur->ss = cur->ds = cur->es = (uint32_t)(USER_DS | 3);
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199 | cur->eflags |= EFL_IF; |
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200 | } |
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201 | |||
202 | void
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203 | context_dump(context_t ctx) |
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204 | { |
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205 | |||
206 | #ifdef DEBUG
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207 | trap_dump(ctx->uregs); |
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208 | #endif
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209 | } |