Question

uboot启动 start.S 文件分析

194 #ifndef CONFIG_PRELOADER
195 /*
196 * fix .rel.dyn relocations
197 */
198 ldr r0, _TEXT_BASE /* r0 <- Text base */
199 sub r9, r6, r0 /* r9 <- relocation offset */
200 ldr r10, _dynsym_start_ofs /* r10 <- sym table ofs */
201 add r10, r10, r0 /* r10 <- sym table in FLASH */
202 ldr r2, _rel_dyn_start_ofs /* r2 <- rel dyn start ofs */
203 add r2, r2, r0 /* r2 <- rel dyn start in FLASH */
204 ldr r3, _rel_dyn_end_ofs /* r3 <- rel dyn end ofs */
205 add r3, r3, r0 /* r3 <- rel dyn end in FLASH */
206 fixloop:
207 ldr r0, [r2] /* r0 <- location to fix up, IN FLASH! */
208 add r0, r0, r9 /* r0 <- location to fix up in RAM */
209 ldr r1, [r2, #4]
210 and r7, r1, #0xff
211 cmp r7, #23 /* relative fixup? */
212 beq fixrel
213 cmp r7, #2 /* absolute fixup? */
214 beq fixabs
215 /* ignore unknown type of fixup */
216 b fixnext
217 fixabs:
218 /* absolute fix: set location to (offset) symbol value */
219 mov r1, r1, LSR #4 /* r1 <- symbol index in .dynsym */
220 add r1, r10, r1 /* r1 <- address of symbol in table */
221 ldr r1, [r1, #4] /* r1 <- symbol value */
222 add r1, r1, r9 /* r1 <- relocated sym addr */
223 b fixnext
224 fixrel:
225 /* relative fix: increase location by offset */
226 ldr r1, [r0]
227 add r1, r1, r9
228 fixnext:
229 str r1, [r0]
230 add r2, r2, #8 /* each rel.dyn entry is 8 bytes */
231 cmp r2, r3
232 blo fixloop
233
234 clear_bss:
235 ldr r0, _bss_start_ofs //清空Bass段
236 ldr r1, _bss_end_ofs
237 ldr r3, _TEXT_BASE /* Text base */
238 mov r4, r6 /* reloc addr */
239 add r0, r0, r4
240 add r1, r1, r4
241 mov r2, #0x00000000 /* clear */
242
243 clbss_l:str r2, [r0] /* clear loop... */
244 add r0, r0, #4
245 cmp r0, r1
246 bne clbss_l
247 #endif /* #ifndef CONFIG_PRELOADER */

谁给我解释，谢谢！

Answer 1

这么长的纤斗汪代码毁仔就给十分，自己要是一点都看不懂建议你先去学学汇编，要是能看懂一些，就把你看的时候产销胡生的疑问提出来，让大家帮你，别把网友当苦力，谢谢！

追问

呵呵，我已经明白了。

追答

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