链接地址和运行地址

1、运行地址<--->链接地址：他们两个是等价的，只是两种不同的说法。

2、加载地址<--->存储地址：他们两个是等价的，也是两种不同的说法。

运行地址：程序在SRAM、SDRAM中执行时的地址。

就是执行这条指令时，PC应该等于这个地址，换句话说，PC等于这个地址时，这条指令应该保存在这个地址内。

加载地址：程序保存在Nand flash中的地址。

位置无关码：B、BL、MOV都是位置位置无关码。

位置有关码：LDR PC,=LABEL等类似的代码都是位置有关码。

下面我们来看看一个Makefile文件sdram.bin : head.S leds.carm-linux-gcc -c -o head.o head.Sarm-linux-gcc -c -o leds.o leds.carm-linux-ld -Ttext 0x30000000 head.o leds.o -o sdram_elfarm-linux-objcopy -O binary -S sdram_elf sdram.binarm-linux-objdump -D -m arm sdram_elf > sdram.disclean:rm -f sdram.dis sdram.bin sdram_elf *.o我们可以看到sdram_elf的代码段是从0x30000000地址开始存放，这个地址我们称之为运行地址。

为什么从这个地址开始存放，因为SDRAM的起始地址是0x30000000.下面来看看一个启动代码@*************************************************************************@ File：head.S@ 功能：设置SDRAM，将程序复制到SDRAM，然后跳到SDRAM继续执行@*************************************************************************.equ MEM_CTL_BASE, 0x48000000.equ SDRAM_BASE, 0x30000000.text.global _start_start:bl disable_watch_dog @ 关闭WATCHDOG，否则CPU会不断重启bl memsetup @ 设置存储控制器bl copy_steppingstone_to_sdram @ 复制代码到SDRAM中ldr pc, =on_sdram @ 跳到SDRAM中继续执行on_sdram:ldr sp, =0x34000000 @ 设置堆栈bl mainhalt_loop:b halt_loopdisable_watch_dog:@ 往WATCHDOG寄存器写0即可mov r1, #0x53000000mov r2, #0x0str r2, [r1]mov pc, lr @ 返回copy_steppingstone_to_sdram:@ 将Steppingstone的4K数据全部复制到SDRAM中去@ Steppingstone起始地址为0x00000000，SDRAM中起始地址为0x30000000mov r1, #0ldr r2, =SDRAM_BASEmov r3, #4*10241:ldr r4, [r1],#4 @ 从Steppingstone读取4字节的数据，并让源地址加4str r4, [r2],#4 @ 将此4字节的数据复制到SDRAM中，并让目地地址加4cmp r1, r3 @ 判断是否完成：源地址等于Steppingstone的未地址？bne 1b @ 若没有复制完，继续mov pc, lr @ 返回memsetup:@ 设置存储控制器以便使用SDRAM等外设mov r1, #MEM_CTL_BASE @ 存储控制器的13个寄存器的开始地址adrl r2, mem_cfg_val @ 这13个值的起始存储地址add r3, r1, #52 @ 13*4 = 541:ldr r4, [r2], #4 @ 读取设置值，并让r2加4 str r4, [r1], #4 @ 将此值写入寄存器，并让r1加4cmp r1, r3 @ 判断是否设置完所有13个寄存器bne 1b @ 若没有写成，继续mov pc, lr @ 返回.align 4mem_cfg_val:@ 存储控制器13个寄存器的设置值.long 0x22011110 @ BWSCON.long 0x00000700 @ BANKCON0.long 0x00000700 @ BANKCON1.long 0x00000700 @ BANKCON2.long 0x00000700 @ BANKCON3.long 0x00000700 @ BANKCON4.long 0x00000700 @ BANKCON5.long 0x00018005 @ BANKCON6.long 0x00018005 @ BANKCON7.long 0x008C07A3 @ REFRESH.long 0x000000B1 @ BANKSIZE.long 0x00000030 @ MRSRB6.long 0x00000030 @ MRSRB7下面来看看反汇编代码sdram_elf: file format elf32-littlearmDisassembly of section .text:30000000 <_start>:30000000: eb000005 bl 3000001c <disable_watch_dog> 30000004: eb000010 bl 3000004c <memsetup>30000008: eb000007 bl 3000002c <copy_steppingstone_to_sdram> 3000000c: e59ff090 ldr pc, [pc, #144] ; 300000a4<mem_cfg_val+0x34>30000010 <on_sdram>:30000010: e3a0d30d mov sp, #872415232 ; 0x34000000 30000014: eb000033 bl 300000e8 <main>30000018 <halt_loop>:30000018: eafffffe b 30000018 <halt_loop>3000001c <disable_watch_dog>:3000001c: e3a01453 mov r1, #1392508928 ; 0x53000000 30000020: e3a02000 mov r2, #030000024: e5812000 str r2, [r1]30000028: e1a0f00e mov pc, lr3000002c <copy_steppingstone_to_sdram>:3000002c: e3a01000 mov r1, #030000030: e3a02203 mov r2, #805306368 ; 0x30000000 30000034: e3a03a01 mov r3, #4096 ; 0x100030000038: e4914004 ldr r4, [r1], #43000003c: e4824004 str r4, [r2], #430000040: e1510003 cmp r1, r330000044: 1afffffb bne 30000038<copy_steppingstone_to_sdram+0xc>30000048: e1a0f00e mov pc, lr3000004c <memsetup>:3000004c: e3a01312 mov r1, #1207959552 ; 0x48000000 30000050: e28f2018 add r2, pc, #2430000054: e1a00000 nop ; (mov r0, r0) 30000058: e2813034 add r3, r1, #52 ; 0x343000005c: e4924004 ldr r4, [r2], #430000060: e4814004 str r4, [r1], #430000064: e1510003 cmp r1, r330000068: 1afffffb bne 3000005c <memsetup+0x10>3000006c: e1a0f00e mov pc, lr30000070 <mem_cfg_val>:30000070: 22011110 andcs r1, r1, #430000074: 00000700 andeq r0, r0, r0, lsl #1430000078: 00000700 andeq r0, r0, r0, lsl #143000007c: 00000700 andeq r0, r0, r0, lsl #1430000080: 00000700 andeq r0, r0, r0, lsl #1430000084: 00000700 andeq r0, r0, r0, lsl #1430000088: 00000700 andeq r0, r0, r0, lsl #143000008c: 00018005 andeq r8, r1, r530000090: 00018005 andeq r8, r1, r530000094: 008c07a3 addeq r0, ip, r3, lsr #1530000098: 000000b1 strheq r0, [r0], -r13000009c: 00000030 andeq r0, r0, r0, lsr r0300000a0: 00000030 andeq r0, r0, r0, lsr r0300000a4: 30000010 andcc r0, r0, r0, lsl r0300000a8: e1a00000 nop ; (mov r0, r0) 300000ac: e1a00000 nop ; (mov r0, r0)300000b0 <wait>:300000b0: e52db004 push {fp} ; (str fp, [sp, #-4]!)300000b4: e28db000 add fp, sp, #0300000b8: e24dd00c sub sp, sp, #12300000bc: e50b0008 str r0, [fp, #-8]300000c0: ea000002 b 300000d0 <wait+0x20>300000c4: e51b3008 ldr r3, [fp, #-8]300000c8: e2433001 sub r3, r3, #1300000cc: e50b3008 str r3, [fp, #-8]300000d0: e51b3008 ldr r3, [fp, #-8]300000d4: e3530000 cmp r3, #0300000d8: 1afffff9 bne 300000c4 <wait+0x14>300000dc: e28bd000 add sp, fp, #0300000e0: e8bd0800 pop {fp}300000e4: e12fff1e bx lr300000e8 <main>:300000e8: e92d4800 push {fp, lr}300000ec: e28db004 add fp, sp, #4300000f0: e24dd008 sub sp, sp, #8300000f4: e3a03000 mov r3, #0300000f8: e50b3008 str r3, [fp, #-8]300000fc: e59f3030 ldr r3, [pc, #48] ; 30000134 <main+0x4c>30000100: e3a02b55 mov r2, #87040 ; 0x15400 30000104: e5832000 str r2, [r3]30000108: e59f0028 ldr r0, [pc, #40] ; 30000138 <main+0x50>3000010c: ebffffe7 bl 300000b0 <wait>30000110: e59f3024 ldr r3, [pc, #36] ; 3000013c <main+0x54>30000114: e3a02000 mov r2, #030000118: e5832000 str r2, [r3]3000011c: e59f0014 ldr r0, [pc, #20] ; 30000138 <main+0x50>30000120: ebffffe2 bl 300000b0 <wait>30000124: e59f3010 ldr r3, [pc, #16] ; 3000013c <main+0x54>30000128: e3a02e1e mov r2, #480 ; 0x1e03000012c: e5832000 str r2, [r3]30000130: eafffff4 b 30000108 <main+0x20>30000134: 56000010 undefined instruction 0x5600001030000138: 00007530 andeq r7, r0, r0, lsr r53000013c: 56000014 undefined instruction 0x56000014Disassembly of section .ARM.attributes:00000000 <.ARM.attributes>:0: 00002541 andeq r2, r0, r1, asr #104: 61656100 cmnvs r5, r0, lsl #28: 01006962 tsteq r0, r2, ror #18c: 0000001b andeq r0, r0, fp, lsl r010: 00543405 subseq r3, r4, r5, lsl #814: 01080206 tsteq r8, r6, lsl #418: 04120109 ldreq r0, [r2], #-265 ; 0x1091c: 01150114 tsteq r5, r4, lsl r120: 01180317 tsteq r8, r7, lsl r324: Address 0x00000024 is out of bounds.Disassembly of section .comment:00000000 <.comment>:0: 3a434347 bcc 10d0d24 <SDRAM_BASE-0x2ef2f2dc>4: 74632820 strbtvc r2, [r3], #-2080 ; 0x8208: 312d676e teqcc sp, lr, ror #14c: 312e362e teqcc lr, lr, lsr #1210: 2e342029 cdpcs 0, 3, cr2, cr4, cr9, {1}14: 00332e34 eorseq r2, r3, r4, lsr lr当我们从Nand flash启动时，硬件会自动将Nand flash前4kB代码拷贝到片内SRAM中，然后CPU从SRAM的0x00000000地址处开始执行程序。