ARM Assembly中的Seg故障

Question

所以，我试图学习ARM程序集，基本上我想要做的就是使用纯组件来打开BeagleBone Black的LED。我知道如何用C语言编程，但如果这有什么不同，我对ARM汇编很陌生。

基本上我只是试图修改字符串中的字符，但它似乎并没有工作。也许是因为我没有完全理解内存管理指令。

当我运行代码时，它给了我一个分段错误。

这里是我的代码：

.syntax unified 

    .global main 

main: 
    push {ip, lr} 

    mov  r0, beagle_bone_0 
    mov  r1, #0x65 
    strb r1, [r0] 
    ldr  r0, =beagle_bone_0 

    bl  printf 

    pop  {ip, pc} 

beagle_bone_0: 
    .asciz "/sys/class/leds/beaglebone:green:usr0/brightness" 

objdump的-x输出：

helloworld:  file format elf32-littlearm 
helloworld 
architecture: arm, flags 0x00000112: 
EXEC_P, HAS_SYMS, D_PAGED 
start address 0x00008325 

Program Header: 
0x70000001 off 0x00000444 vaddr 0x00008444 paddr 0x00008444 align 2**2 
     filesz 0x00000008 memsz 0x00000008 flags r-- 
    PHDR off 0x00000034 vaddr 0x00008034 paddr 0x00008034 align 2**2 
     filesz 0x00000100 memsz 0x00000100 flags r-x 
    INTERP off 0x00000134 vaddr 0x00008134 paddr 0x00008134 align 2**0 
     filesz 0x00000019 memsz 0x00000019 flags r-- 
    LOAD off 0x00000000 vaddr 0x00008000 paddr 0x00008000 align 2**15 
     filesz 0x00000450 memsz 0x00000450 flags r-x 
    LOAD off 0x00000450 vaddr 0x00010450 paddr 0x00010450 align 2**15 
     filesz 0x00000124 memsz 0x00000128 flags rw- 
DYNAMIC off 0x0000045c vaddr 0x0001045c paddr 0x0001045c align 2**2 
     filesz 0x000000f0 memsz 0x000000f0 flags rw- 
    NOTE off 0x00000150 vaddr 0x00008150 paddr 0x00008150 align 2**2 
     filesz 0x00000044 memsz 0x00000044 flags r-- 
    STACK off 0x00000000 vaddr 0x00000000 paddr 0x00000000 align 2**2 
     filesz 0x00000000 memsz 0x00000000 flags rwx 

Dynamic Section: 
    NEEDED    libc.so.6 
    INIT     0x000082d1 
    FINI     0x00008439 
    INIT_ARRAY   0x00010450 
    INIT_ARRAYSZ   0x00000004 
    FINI_ARRAY   0x00010454 
    FINI_ARRAYSZ   0x00000004 
    HASH     0x00008194 
    GNU_HASH    0x000081bc 
    STRTAB    0x00008238 
    SYMTAB    0x000081e8 
    STRSZ    0x00000043 
    SYMENT    0x00000010 
    DEBUG    0x00000000 
    PLTGOT    0x0001054c 
    PLTRELSZ    0x00000020 
    PLTREL    0x00000011 
    JMPREL    0x000082b0 
    REL     0x000082a8 
    RELSZ    0x00000008 
    RELENT    0x00000008 
    VERNEED    0x00008288 
    VERNEEDNUM   0x00000001 
    VERSYM    0x0000827c 

Version References: 
    required from libc.so.6: 
    0x0d696914 0x00 02 GLIBC_2.4 
private flags = 5000002: [Version5 EABI] [has entry point] 

Sections: 
Idx Name   Size  VMA  LMA  File off Algn 
    0 .interp  00000019 00008134 00008134 00000134 2**0 
        CONTENTS, ALLOC, LOAD, READONLY, DATA 
    1 .note.ABI-tag 00000020 00008150 00008150 00000150 2**2 
        CONTENTS, ALLOC, LOAD, READONLY, DATA 
    2 .note.gnu.build-id 00000024 00008170 00008170 00000170 2**2 
        CONTENTS, ALLOC, LOAD, READONLY, DATA 
    3 .hash   00000028 00008194 00008194 00000194 2**2 
        CONTENTS, ALLOC, LOAD, READONLY, DATA 
    4 .gnu.hash  0000002c 000081bc 000081bc 000001bc 2**2 
        CONTENTS, ALLOC, LOAD, READONLY, DATA 
    5 .dynsym  00000050 000081e8 000081e8 000001e8 2**2 
        CONTENTS, ALLOC, LOAD, READONLY, DATA 
    6 .dynstr  00000043 00008238 00008238 00000238 2**0 
        CONTENTS, ALLOC, LOAD, READONLY, DATA 
    7 .gnu.version 0000000a 0000827c 0000827c 0000027c 2**1 
        CONTENTS, ALLOC, LOAD, READONLY, DATA 
    8 .gnu.version_r 00000020 00008288 00008288 00000288 2**2 
        CONTENTS, ALLOC, LOAD, READONLY, DATA 
    9 .rel.dyn  00000008 000082a8 000082a8 000002a8 2**2 
        CONTENTS, ALLOC, LOAD, READONLY, DATA 
10 .rel.plt  00000020 000082b0 000082b0 000002b0 2**2 
        CONTENTS, ALLOC, LOAD, READONLY, DATA 
11 .init   0000000a 000082d0 000082d0 000002d0 2**2 
        CONTENTS, ALLOC, LOAD, READONLY, CODE 
12 .plt   00000048 000082dc 000082dc 000002dc 2**2 
        CONTENTS, ALLOC, LOAD, READONLY, CODE 
13 .text   00000114 00008324 00008324 00000324 2**2 
        CONTENTS, ALLOC, LOAD, READONLY, CODE 
14 .fini   00000006 00008438 00008438 00000438 2**2 
        CONTENTS, ALLOC, LOAD, READONLY, CODE 
15 .rodata  00000004 00008440 00008440 00000440 2**2 
        CONTENTS, ALLOC, LOAD, READONLY, DATA 
16 .ARM.exidx 00000008 00008444 00008444 00000444 2**2 
        CONTENTS, ALLOC, LOAD, READONLY, DATA 
17 .eh_frame  00000004 0000844c 0000844c 0000044c 2**2 
        CONTENTS, ALLOC, LOAD, READONLY, DATA 
18 .init_array 00000004 00010450 00010450 00000450 2**2 
        CONTENTS, ALLOC, LOAD, DATA 
19 .fini_array 00000004 00010454 00010454 00000454 2**2 
        CONTENTS, ALLOC, LOAD, DATA 
20 .jcr   00000004 00010458 00010458 00000458 2**2 
        CONTENTS, ALLOC, LOAD, DATA 
21 .dynamic  000000f0 0001045c 0001045c 0000045c 2**2 
        CONTENTS, ALLOC, LOAD, DATA 
22 .got   00000020 0001054c 0001054c 0000054c 2**2 
        CONTENTS, ALLOC, LOAD, DATA 
23 .data   00000008 0001056c 0001056c 0000056c 2**2 
        CONTENTS, ALLOC, LOAD, DATA 
24 .bss   00000004 00010574 00010574 00000574 2**0 
        ALLOC 
25 .comment  0000001d 00000000 00000000 00000574 2**0 
        CONTENTS, READONLY 
26 .ARM.attributes 00000031 00000000 00000000 00000591 2**0 
        CONTENTS, READONLY 
SYMBOL TABLE: 
00008134 l d .interp 00000000    .interp 
00008150 l d .note.ABI-tag 00000000    .note.ABI-tag 
00008170 l d .note.gnu.build-id 00000000    .note.gnu.build-id 
00008194 l d .hash 00000000    .hash 
000081bc l d .gnu.hash 00000000    .gnu.hash 
000081e8 l d .dynsym 00000000    .dynsym 
00008238 l d .dynstr 00000000    .dynstr 
0000827c l d .gnu.version 00000000    .gnu.version 
00008288 l d .gnu.version_r 00000000    .gnu.version_r 
000082a8 l d .rel.dyn 00000000    .rel.dyn 
000082b0 l d .rel.plt 00000000    .rel.plt 
000082d0 l d .init 00000000    .init 
000082dc l d .plt 00000000    .plt 
00008324 l d .text 00000000    .text 
00008438 l d .fini 00000000    .fini 
00008440 l d .rodata 00000000    .rodata 
00008444 l d .ARM.exidx 00000000    .ARM.exidx 
0000844c l d .eh_frame 00000000    .eh_frame 
00010450 l d .init_array 00000000    .init_array 
00010454 l d .fini_array 00000000    .fini_array 
00010458 l d .jcr 00000000    .jcr 
0001045c l d .dynamic 00000000    .dynamic 
0001054c l d .got 00000000    .got 
0001056c l d .data 00000000    .data 
00010574 l d .bss 00000000    .bss 
00000000 l d .comment 00000000    .comment 
00000000 l d .ARM.attributes 00000000    .ARM.attributes 
0000835c l  F .text 00000000    call_gmon_start 
00000000 l df *ABS* 00000000    crtstuff.c 
00010458 l  O .jcr 00000000    __JCR_LIST__ 
00008374 l  F .text 00000000    __do_global_dtors_aux 
00010574 l  O .bss 00000001    completed.5637 
00010454 l  O .fini_array 00000000    __do_global_dtors_aux_fini_array_entry 
00008384 l  F .text 00000000    frame_dummy 
00010450 l  O .init_array 00000000    __frame_dummy_init_array_entry 
000083b8 l  .text 00000000    beagle_bone_0 
00000000 l df *ABS* 00000000    crtstuff.c 
0000844c l  O .eh_frame 00000000    __FRAME_END__ 
00010458 l  O .jcr 00000000    __JCR_END__ 
00010454 l  .init_array 00000000    __init_array_end 
0001045c l  O .dynamic 00000000    _DYNAMIC 
00010450 l  .init_array 00000000    __init_array_start 
0001054c l  O .got 00000000    _GLOBAL_OFFSET_TABLE_ 
00008434 g  F .text 00000002    __libc_csu_fini 
0001056c w  .data 00000000    data_start 
000082f0  F *UND* 00000000    printf@@GLIBC_2.4 
00010574 g  *ABS* 00000000    __bss_start__ 
00010578 g  *ABS* 00000000    _bss_end__ 
00010574 g  *ABS* 00000000    _edata 
00008438 g  F .fini 00000000    _fini 
00010578 g  *ABS* 00000000    __bss_end__ 
0001056c g  .data 00000000    __data_start 
000082fc  F *UND* 00000000    __libc_start_main@@GLIBC_2.4 
00000000 w  *UND* 00000000    __gmon_start__ 
00010570 g  O .data 00000000    .hidden __dso_handle 
00008440 g  O .rodata 00000004    _IO_stdin_used 
000083f0 g  F .text 00000044    __libc_csu_init 
00010578 g  *ABS* 00000000    _end 
00008324 g  F .text 00000000    _start 
00010578 g  *ABS* 00000000    __end__ 
00010574 g  *ABS* 00000000    __bss_start 
0000839c g  .text 00000000    main 
00000000 w  *UND* 00000000    _Jv_RegisterClasses 
00008318  F *UND* 00000000    abort@@GLIBC_2.4 
000082d0 g  F .init 00000000    _init 

Answer 1

我跑和调试代码。行mov r0, beagle_bone_0甚至没有编译（至少在我的编译器上）。你想在r0中加载beagle_bone的地址。对于这一点，你应该这样使用adr伪指令，即通过在PC相对移动的编译器编译（类似mov r0, [pc, #8]。你不能使用这种方式，也许你的编译器把它翻译成不同的东西。

，解决它，只是adr r0, beagle_bone_0更换线mov r0, beagle_bone_0。

而且字符串是在.text段，我们无法进行编辑。所以，我在.data节放beagle_bone_0。

Answer 2

这个问题的答案我问题其实很简单，因为ldr r0，= beagle_bone_0将beagle_bone_0的地址加载到寄存器0中，我可以操作带有该地址的beagle_bone_0。

工作的测试代码：

.syntax unified 

    .data 

beagle_bone_0: .ascii "Hello, world\n" 

    .text 

    .global main 

main: 
    push {ip, lr} 

    ldr  r0, =beagle_bone_0 
    mov  r1, #0x65 
    strb r1, [r0] 

    bl  printf 

    pop  {ip, pc}