linux修改代码段,自修改代码总是在Linux上出现分段错误

我找到了一篇有关自我修改代码的文章，并尝试做一些示例，但是我总是遇到分段错误。据我所了解，fas违反了内存权限。代码段是(r)ead /

e(x)ecute，因此尝试将结果写入此错误。是否可以通过在运行时或之前更改内存许可来测试程序？我使用的是linux，示例是用GAS汇编编写的。

.extern memcpy

.section .data

string:

.asciz "whatever"

string_end:

.section .bss

.lcomm buf, string_end-string

.section .text

.globl main

main:

call changer

mov $string, %edx

label:

push string_end-string

push $buf

push $string

call memcpy

changer:

mov $offset_to_write, %esi

mov $label, %edi

mov $0xb, %ecx

loop1:

lodsb

stosb

loop loop1

ret

offset_to_write:

push 0

call exit

end:

因此，在osgx建议的修改之后，这是一个有效的代码(实际上，如果您汇编并链接并运行它会崩溃，但是如果您使用gdb观看它会修改其代码！)

.extern memcpy

.section .data

string:

.asciz "Giorgos"

string_end:

.section .bss

.lcomm buf, string_end-string

.section .text

.globl main

main:

lea (main), %esi # get the start of memory region to

# change its permissions (smc-enabled)

andl $0xFFFFF000, %esi # align to start of a pagesize

pushl $7 # permissions==r|w|x

pushl $4096 # page size

pushl %esi # computed start address

call mprotect

call changer # function that does smc

mov $string, %edx

label:

push string_end-string # this code will be overridden

push $buf # and never be executed!

push $string

call memcpy

changer:

mov $offset_to_write, %esi # simple copy bytes algorithm

mov $label, %edi

mov $0xb, %ecx

loop1:

lodsb

stosb

loop loop1

ret

offset_to_write: # these instructions will be

push $0 # executed eventually

call exit

end: