计算机系统篇之链接（8）：位置无关代码（中）——真正理解 PIC 数据引用的工作原理（Linux X86-64 示例）
Author: stormQ
Created: Wednesday, 15. April 2020 04:35PM
Last Modified: Sunday, 01. November 2020 11:34AM
本文以 Linux X86-64 程序为例，利用 gdb 详细分析了位置无关代码技术中数据引用的过程，从而真正理解位置无关代码的工作原理。
step 1: 生成共享库
1）第一个共享库的源文件——add.cpp:
int g_sum = 0;
int add(int a, int b)
{
g_sum = a + b;
return g_sum;
}
生成第一个共享库——libadd_debug.so
$ g++ -fpic -shared -g -o libadd_debug.so add.cpp
2）第二个共享库的源文件——sub.cpp:
int g_sub = 0;
int sub(int a, int b)
{
g_sub = a - b;
return g_sub;
}
生成第二个共享库——libsub_debug.so
$ g++ -fpic -shared -g -o libsub_debug.so sub.cpp
step 2: 生成测试程序（用于调用以上两个共享库）——main_mix
测试程序的源文件——main_mix.cpp:
extern int add(int, int);
extern int sub(int, int);
int main()
{
add(0xb, 0xc);
add(0xb, 0xc);
sub(0xf, 0xd);
sub(0xf, 0xd);
return 0;
}
生成测试程序——main_mix
$ g++ -o main_mix main_mix.cpp ./libadd_debug.so ./libsub_debug.so -g
step 3: 查看共享库的代码段
1）查看共享库libadd_debug.so的代码段
# 查看共享库中可执行的sections（包含了.text section）
$ objdump -d libadd_debug.so
输出结果为（只保留add()函数的汇编代码）：
; ...... Skip
Disassembly of section .text:
; ...... Skip
0000000000000640 <_Z3addii>:
640: 55 push %rbp
641: 48 89 e5 mov %rsp,%rbp
644: 89 7d fc mov %edi,-0x4(%rbp)
647: 89 75 f8 mov %esi,-0x8(%rbp)
64a: 8b 55 fc mov -0x4(%rbp),%edx
64d: 8b 45 f8 mov -0x8(%rbp),%eax
650: 01 c2 add %eax,%edx
652: 48 8b 05 7f 09 20 00 mov 0x20097f(%rip),%rax # 200fd8 <_DYNAMIC+0x158>
659: 89 10 mov %edx,(%rax)
65b: 48 8b 05 76 09 20 00 mov 0x200976(%rip),%rax # 200fd8 <_DYNAMIC+0x158>
662: 8b 00 mov (%rax),%eax
664: 5d pop %rbp
665: c3 retq
; ...... Skip
输出结果分析：
mov 0x20097f(%rip),%rax的作用：将共享库libadd_debug.so的GOT[1]的内容——即全局变量 g_sum 的地址传送到 %rax 寄存器中。
mov %edx,(%rax)的作用：将%edx寄存器的值（存放着a+b的计算结果）赋值给全局变量g_sum。
推导过程：
a）首先查看共享库中.got section的位置
$ readelf -S libadd_debug.so
输出结果为：
Section Headers:
[Nr] Name Type Address Offset
Size EntSize Flags Link Info Align
; ......
[17] .got PROGBITS 0000000000200fd0 00000fd0
0000000000000030 0000000000000008 WA 0 0 8
; ......
从输出结果中可以看出，共享库中存放.got section的起始地址为0x200fd0——即共享库中.got section的起始位置相对于共享库加载地址的偏移量为0x200fd0，.got section的大小为0x30——即.got中的条目个数为6（.got的每个条目占8字节）。
b）接下来查看共享库中的重定位信息
readelf -r libadd_debug.so
输出结果为：
Relocation section '.rela.dyn' at offset 0x420 contains 9 entries:
Offset Info Type Sym. Value Sym. Name + Addend
000000200e68 000000000008 R_X86_64_RELATIVE 610
000000200e70 000000000008 R_X86_64_RELATIVE 5d0
000000201018 000000000008 R_X86_64_RELATIVE 201018
000000200fd0 000200000006 R_X86_64_GLOB_DAT 0000000000000000 __cxa_finalize + 0
000000200fd8 000700000006 R_X86_64_GLOB_DAT 0000000000201024 g_sum + 0
000000200fe0 000300000006 R_X86_64_GLOB_DAT 0000000000000000 _ITM_registerTMCloneTa + 0
000000200fe8 000400000006 R_X86_64_GLOB_DAT 0000000000000000 _ITM_deregisterTMClone + 0
000000200ff0 000500000006 R_X86_64_GLOB_DAT 0000000000000000 _Jv_RegisterClasses + 0
000000200ff8 000600000006 R_X86_64_GLOB_DAT 0000000000000000 __gmon_start__ + 0
从输出结果中可以看出，共享库中全局变量g_sum相对于共享库加载地址的偏移量为0x200fd8，并且重定位方式为R_X86_64_GLOB_DAT。R_X86_64_GLOB_DAT的含义：一旦知道g_sum的运行时地址，就把它放入0x200fd8处（R_X86_64_GLOB_DAT：The relocation type is used to set a global offset table entry to the address of the specified symbol. The special relocation type allows one to determine the correspondence between symbols and global offset table entries.）。
c）所以可以得出，结论1：共享库libadd_debug.so中的GOT[1]条目（位于进程虚拟地址空间中的共享库的内存映射区域）是用于保存全局变量g_sum的运行时地址的。
d）mov 0x20097f(%rip),%rax指令中0x20097f的计算过程：共享库中GOT[1]条目的地址（0x200fd8）减去共享模块中下一条指令（即mov %edx,(%rax)）的地址（0x659），计算结果为0x20097f（这种寻址方式被称为“PC相对寻址”）——意味着共享库中GOT[1]条目与共享库中下一条指令之间的距离或偏移量为0x20097f，该偏移量在生成共享库时就可以确定，并且在加载共享库时不会发生变化。编译器这是利用了这一事实，来实现“PIC 数据引用”的。
e）mov 0x20097f(%rip),%rax指令中0x20097f(%rip)的作用：运行时%rip寄存器（即PC寄存器）中存放着下一条指令在内存中的运行时地址，0x20097f(%rip)表示以%rip寄存器的值加上0x20097f作为起始地址，并取该地址后面的8字节——即GOT[1]条目的运行时地址。接下来通过GOT[1]条目的内容——&g_sum来访问全局变量g_sum，也就是mov %edx,(%rax)（将%edx寄存器的值（存放着a+b的计算结果）赋值给全局变量g_sum）的作用。
2）同理，分析共享库libsub_debug.so后，可以得出，结论2：共享库libsub_debug.so中的GOT[1]条目（位于进程虚拟地址空间中的共享库的内存映射区域）是用于保存全局变量g_sub的运行时地址的。
step 4: 分析共享库是如何访问全局变量的
1）使用 gdb（使用了GEF插件）运行测试程序——main_mix
$ gdb -q main_mix
gef➤ start
2）反汇编add函数
反汇编add函数，并在0x00007ffff7bd5652和0x00007ffff7bd5659处设置断点。
gef➤ disas add
Dump of assembler code for function add(int, int):
0x00007ffff7bd5640 <+0>: push rbp
0x00007ffff7bd5641 <+1>: mov rbp,rsp
0x00007ffff7bd5644 <+4>: mov DWORD PTR [rbp-0x4],edi
0x00007ffff7bd5647 <+7>: mov DWORD PTR [rbp-0x8],esi
0x00007ffff7bd564a <+10>: mov edx,DWORD PTR [rbp-0x4]
0x00007ffff7bd564d <+13>: mov eax,DWORD PTR [rbp-0x8]
0x00007ffff7bd5650 <+16>: add edx,eax
0x00007ffff7bd5652 <+18>: mov rax,QWORD PTR [rip+0x20097f] # 0x7ffff7dd5fd8
0x00007ffff7bd5659 <+25>: mov DWORD PTR [rax],edx
0x00007ffff7bd565b <+27>: mov rax,QWORD PTR [rip+0x200976] # 0x7ffff7dd5fd8
0x00007ffff7bd5662 <+34>: mov eax,DWORD PTR [rax]
0x00007ffff7bd5664 <+36>: pop rbp
0x00007ffff7bd5665 <+37>: ret
End of assembler dump.
gef➤ b *0x00007ffff7bd5652
gef➤ b *0x00007ffff7bd5659
3）反汇编sub函数
反汇编sub函数，并在0x00007ffff79d3652和0x00007ffff79d3659处设置断点。
gef➤ disas sub
Dump of assembler code for function sub(int, int):
0x00007ffff79d3640 <+0>: push rbp
0x00007ffff79d3641 <+1>: mov rbp,rsp
0x00007ffff79d3644 <+4>: mov DWORD PTR [rbp-0x4],edi
0x00007ffff79d3647 <+7>: mov DWORD PTR [rbp-0x8],esi
0x00007ffff79d364a <+10>: mov eax,DWORD PTR [rbp-0x4]
0x00007ffff79d364d <+13>: sub eax,DWORD PTR [rbp-0x8]
0x00007ffff79d3650 <+16>: mov edx,eax
0x00007ffff79d3652 <+18>: mov rax,QWORD PTR [rip+0x20097f] # 0x7ffff7bd3fd8
0x00007ffff79d3659 <+25>: mov DWORD PTR [rax],edx
0x00007ffff79d365b <+27>: mov rax,QWORD PTR [rip+0x200976] # 0x7ffff7bd3fd8
0x00007ffff79d3662 <+34>: mov eax,DWORD PTR [rax]
0x00007ffff79d3664 <+36>: pop rbp
0x00007ffff79d3665 <+37>: ret
End of assembler dump.
gef➤ b *0x00007ffff79d3652
gef➤ b *0x00007ffff79d3659
4）分析共享库libadd_debug.so是如何访问全局变量g_sum的
a）继续执行程序（断点1会被击中），查看当前运行的汇编代码
gef➤ c
gef➤ disas
Dump of assembler code for function add(int, int):
0x00007ffff7bd5640 <+0>: push rbp
0x00007ffff7bd5641 <+1>: mov rbp,rsp
0x00007ffff7bd5644 <+4>: mov DWORD PTR [rbp-0x4],edi
0x00007ffff7bd5647 <+7>: mov DWORD PTR [rbp-0x8],esi
0x00007ffff7bd564a <+10>: mov edx,DWORD PTR [rbp-0x4]
0x00007ffff7bd564d <+13>: mov eax,DWORD PTR [rbp-0x8]
0x00007ffff7bd5650 <+16>: add edx,eax
=> 0x00007ffff7bd5652 <+18>: mov rax,QWORD PTR [rip+0x20097f] # 0x7ffff7dd5fd8
0x00007ffff7bd5659 <+25>: mov DWORD PTR [rax],edx
0x00007ffff7bd565b <+27>: mov rax,QWORD PTR [rip+0x200976] # 0x7ffff7dd5fd8
0x00007ffff7bd5662 <+34>: mov eax,DWORD PTR [rax]
0x00007ffff7bd5664 <+36>: pop rbp
0x00007ffff7bd5665 <+37>: ret
End of assembler dump.
b）计算用于保存全局变量g_sum运行时地址的GOT条目的地址
; 执行 mov rax,QWORD PTR [rip+0x20097f] 时，%rip寄存器（即PC寄存器）中存放着下一条指令（mov DWORD PTR [rax],edx）的运行时地址（0x00007ffff7bd5659）。此时，打印%rip寄存器的值，会发现其值为0x00007ffff7bd5652，这是因为当前指令（最左侧带=>的）还未执行。
gef➤ p /x 0x00007ffff7bd5659+0x20097f ; 1）计算 mov rax,QWORD PTR [rip+0x20097f] 的下一条指令的地址（0x00007ffff7bd5659）与偏移量0x20097f相加的结果
$2 = 0x7ffff7dd5fd8 ; 计算结果为0x7ffff7dd5fd8，即共享库libadd_debug.so中GOT[1]条目的地址为0x7ffff7dd5fd8
为什么0x7ffff7dd5fd8是共享库libadd_debug.so中GOT[1]条目的地址，这一点可以通过查看可执行文件的虚拟内存映射得到验证。
gef➤ vmmap ; 1）查看可执行文件的虚拟内存映射
Start End Offset Perm Path
0x0000000000400000 0x0000000000401000 0x0000000000000000 r-x /home/test/Desktop/localization_sim/main_mix
0x0000000000600000 0x0000000000601000 0x0000000000000000 r-- /home/test/Desktop/localization_sim/main_mix
0x0000000000601000 0x0000000000602000 0x0000000000001000 rw- /home/test/Desktop/localization_sim/main_mix
0x00007ffff7609000 0x00007ffff77c9000 0x0000000000000000 r-x /lib/x86_64-linux-gnu/libc-2.23.so
0x00007ffff77c9000 0x00007ffff79c9000 0x00000000001c0000 --- /lib/x86_64-linux-gnu/libc-2.23.so
0x00007ffff79c9000 0x00007ffff79cd000 0x00000000001c0000 r-- /lib/x86_64-linux-gnu/libc-2.23.so
0x00007ffff79cd000 0x00007ffff79cf000 0x00000000001c4000 rw- /lib/x86_64-linux-gnu/libc-2.23.so
0x00007ffff79cf000 0x00007ffff79d3000 0x0000000000000000 rw-
0x00007ffff79d3000 0x00007ffff79d4000 0x0000000000000000 r-x /home/test/Desktop/localization_sim/libsub_debug.so
0x00007ffff79d4000 0x00007ffff7bd3000 0x0000000000001000 --- /home/test/Desktop/localization_sim/libsub_debug.so
0x00007ffff7bd3000 0x00007ffff7bd4000 0x0000000000000000 r-- /home/test/Desktop/localization_sim/libsub_debug.so
0x00007ffff7bd4000 0x00007ffff7bd5000 0x0000000000001000 rw- /home/test/Desktop/localization_sim/libsub_debug.so
0x00007ffff7bd5000 0x00007ffff7bd6000 0x0000000000000000 r-x /home/test/Desktop/localization_sim/libadd_debug.so
0x00007ffff7bd6000 0x00007ffff7dd5000 0x0000000000001000 --- /home/test/Desktop/localization_sim/libadd_debug.so
0x00007ffff7dd5000 0x00007ffff7dd6000 0x0000000000000000 r-- /home/test/Desktop/localization_sim/libadd_debug.so
0x00007ffff7dd6000 0x00007ffff7dd7000 0x0000000000001000 rw- /home/test/Desktop/localization_sim/libadd_debug.so
0x00007ffff7dd7000 0x00007ffff7dfd000 0x0000000000000000 r-x /lib/x86_64-linux-gnu/ld-2.23.so
0x00007ffff7fd1000 0x00007ffff7fd4000 0x0000000000000000 rw-
0x00007ffff7ff6000 0x00007ffff7ff7000 0x0000000000000000 rw-
0x00007ffff7ff7000 0x00007ffff7ffa000 0x0000000000000000 r-- [vvar]
0x00007ffff7ffa000 0x00007ffff7ffc000 0x0000000000000000 r-x [vdso]
0x00007ffff7ffc000 0x00007ffff7ffd000 0x0000000000025000 r-- /lib/x86_64-linux-gnu/ld-2.23.so
0x00007ffff7ffd000 0x00007ffff7ffe000 0x0000000000026000 rw- /lib/x86_64-linux-gnu/ld-2.23.so
0x00007ffff7ffe000 0x00007ffff7fff000 0x0000000000000000 rw-
0x00007ffffffdd000 0x00007ffffffff000 0x0000000000000000 rw- [stack]
0xffffffffff600000 0xffffffffff601000 0x0000000000000000 r-x [vsyscall]
gef➤ xinfo 0x7ffff7dd5fd8 ; 2）查看地址0x7ffff7dd5fd8的信息
───────────────────────────────────────────────────────────────────────────────── xinfo: 0x7ffff7dd5fd8 ─────────────────────────────────────────────────────────────────────────────────
Page: 0x00007ffff7dd5000 → 0x00007ffff7dd6000 (size=0x1000)
Permissions: r--
Pathname: /home/test/Desktop/localization_sim/libadd_debug.so
Offset (from page): 0xfd8
Inode: 4132975
Segment: .got (0x00007ffff7dd5fd0-0x00007ffff7dd6000)
从输出结果中可以看出，在可执行程序的虚拟内存映射中，共享库libadd_debug.so的.got section的虚拟内存地址范围为0x00007ffff7dd5fd0-0x00007ffff7dd6000。另外，GOT的每个条目占8字节。所以，0x7ffff7dd5fd8是共享库libadd_debug.so的GOT[1]条目的地址。
c）查看全局变量g_sum的值
gef➤ x/gx 0x7ffff7dd5fd8 ; 2）查看该GOT[1]条目的内容，即&g_sum
0x7ffff7dd5fd8: 0x00007ffff7dd6024 ; GOT[1]条目的值为0x00007ffff7dd6024，即全局变量g_sum的运行时地址为0x00007ffff7dd6024
gef➤ p /x &g_sum ; 3）查看全局变量g_sum的运行时地址
$3 = 0x7ffff7dd6024 ; 打印结果也为0x7ffff7dd6024，验证了“GOT[1] = &g_sum”
gef➤ x/wx 0x00007ffff7dd6024 ; 4）查看全局变量g_sum的值
0x7ffff7dd6024 <g_sum>: 0x00000000 ; 全局变量g_sum的值为0x0（g_sum的初始值）
d）至此，验证了“结论1：共享库libadd_debug.so中的GOT[1]条目（位于进程虚拟地址空间中的共享库的内存映射区域）是用于保存全局变量g_sum的运行时地址的”
5）同理，可以分析共享库libsub_debug.so是如何访问全局变量g_sub的
6）查看可执行文件运行期的sections
gef➤ xfiles
Start End Name File
0x0000000000400238 0x0000000000400254 .interp /home/test/Desktop/localization_sim/main_mix
0x0000000000400254 0x0000000000400274 .note.ABI-tag /home/test/Desktop/localization_sim/main_mix
0x0000000000400274 0x0000000000400298 .note.gnu.build-id /home/test/Desktop/localization_sim/main_mix
0x0000000000400298 0x00000000004002d0 .gnu.hash /home/test/Desktop/localization_sim/main_mix
0x00000000004002d0 0x0000000000400408 .dynsym /home/test/Desktop/localization_sim/main_mix
0x0000000000400408 0x00000000004004e4 .dynstr /home/test/Desktop/localization_sim/main_mix
0x00000000004004e4 0x00000000004004fe .gnu.version /home/test/Desktop/localization_sim/main_mix
0x0000000000400500 0x0000000000400520 .gnu.version_r /home/test/Desktop/localization_sim/main_mix
0x0000000000400520 0x0000000000400538 .rela.dyn /home/test/Desktop/localization_sim/main_mix
0x0000000000400538 0x0000000000400580 .rela.plt /home/test/Desktop/localization_sim/main_mix
0x0000000000400580 0x000000000040059a .init /home/test/Desktop/localization_sim/main_mix
0x00000000004005a0 0x00000000004005e0 .plt /home/test/Desktop/localization_sim/main_mix
0x00000000004005e0 0x00000000004005e8 .plt.got /home/test/Desktop/localization_sim/main_mix
0x00000000004005f0 0x0000000000400782 .text /home/test/Desktop/localization_sim/main_mix
0x0000000000400784 0x000000000040078d .fini /home/test/Desktop/localization_sim/main_mix
0x0000000000400790 0x0000000000400794 .rodata /home/test/Desktop/localization_sim/main_mix
0x0000000000400794 0x00000000004007c8 .eh_frame_hdr /home/test/Desktop/localization_sim/main_mix
0x00000000004007c8 0x00000000004008bc .eh_frame /home/test/Desktop/localization_sim/main_mix
0x0000000000600df0 0x0000000000600df8 .init_array /home/test/Desktop/localization_sim/main_mix
0x0000000000600df8 0x0000000000600e00 .fini_array /home/test/Desktop/localization_sim/main_mix
0x0000000000600e00 0x0000000000600e08 .jcr /home/test/Desktop/localization_sim/main_mix
0x0000000000600e08 0x0000000000600ff8 .dynamic /home/test/Desktop/localization_sim/main_mix
0x0000000000600ff8 0x0000000000601000 .got /home/test/Desktop/localization_sim/main_mix
0x0000000000601000 0x0000000000601030 .got.plt /home/test/Desktop/localization_sim/main_mix
0x0000000000601030 0x0000000000601040 .data /home/test/Desktop/localization_sim/main_mix
0x0000000000601040 0x0000000000601048 .bss /home/test/Desktop/localization_sim/main_mix
0x00007ffff7dd71c8 0x00007ffff7dd71ec .note.gnu.build-id /lib64/ld-linux-x86-64.so.2
0x00007ffff7dd71f0 0x00007ffff7dd72b0 .hash /lib64/ld-linux-x86-64.so.2
0x00007ffff7dd72b0 0x00007ffff7dd7390 .gnu.hash /lib64/ld-linux-x86-64.so.2
0x00007ffff7dd7390 0x00007ffff7dd7648 .dynsym /lib64/ld-linux-x86-64.so.2
0x00007ffff7dd7648 0x00007ffff7dd77ef .dynstr /lib64/ld-linux-x86-64.so.2
0x00007ffff7dd77f0 0x00007ffff7dd782a .gnu.version /lib64/ld-linux-x86-64.so.2
0x00007ffff7dd7830 0x00007ffff7dd78d4 .gnu.version_d /lib64/ld-linux-x86-64.so.2
0x00007ffff7dd78d8 0x00007ffff7dd79f8 .rela.dyn /lib64/ld-linux-x86-64.so.2
0x00007ffff7dd79f8 0x00007ffff7dd7a58 .rela.plt /lib64/ld-linux-x86-64.so.2
0x00007ffff7dd7a60 0x00007ffff7dd7ab0 .plt /lib64/ld-linux-x86-64.so.2
0x00007ffff7dd7ab0 0x00007ffff7dd7ab8 .plt.got /lib64/ld-linux-x86-64.so.2
0x00007ffff7dd7ac0 0x00007ffff7df5850 .text /lib64/ld-linux-x86-64.so.2
0x00007ffff7df5860 0x00007ffff7df9920 .rodata /lib64/ld-linux-x86-64.so.2
0x00007ffff7df9920 0x00007ffff7df9921 .stapsdt.base /lib64/ld-linux-x86-64.so.2
0x00007ffff7df9924 0x00007ffff7df9f60 .eh_frame_hdr /lib64/ld-linux-x86-64.so.2
0x00007ffff7df9f60 0x00007ffff7dfc3f8 .eh_frame /lib64/ld-linux-x86-64.so.2
0x00007ffff7ffcbc0 0x00007ffff7ffce6c .data.rel.ro /lib64/ld-linux-x86-64.so.2
0x00007ffff7ffce70 0x00007ffff7ffcfe0 .dynamic /lib64/ld-linux-x86-64.so.2
0x00007ffff7ffcfe0 0x00007ffff7ffcff0 .got /lib64/ld-linux-x86-64.so.2
0x00007ffff7ffd000 0x00007ffff7ffd038 .got.plt /lib64/ld-linux-x86-64.so.2
0x00007ffff7ffd040 0x00007ffff7ffdfc0 .data /lib64/ld-linux-x86-64.so.2
0x00007ffff7ffdfc0 0x00007ffff7ffe168 .bss /lib64/ld-linux-x86-64.so.2
0x00007ffff7ffa120 0x00007ffff7ffa160 .hash /home/test/Desktop/localization_sim/main_mix
0x00007ffff7ffa160 0x00007ffff7ffa1a8 .gnu.hash /home/test/Desktop/localization_sim/main_mix
0x00007ffff7ffa1a8 0x00007ffff7ffa2b0 .dynsym /home/test/Desktop/localization_sim/main_mix
0x00007ffff7ffa2b0 0x00007ffff7ffa30e .dynstr /home/test/Desktop/localization_sim/main_mix
0x00007ffff7ffa30e 0x00007ffff7ffa324 .gnu.version /home/test/Desktop/localization_sim/main_mix
0x00007ffff7ffa328 0x00007ffff7ffa360 .gnu.version_d /home/test/Desktop/localization_sim/main_mix
0x00007ffff7ffa360 0x00007ffff7ffa470 .dynamic /home/test/Desktop/localization_sim/main_mix
0x00007ffff7ffa470 0x00007ffff7ffa7b0 .rodata /home/test/Desktop/localization_sim/main_mix
0x00007ffff7ffa7b0 0x00007ffff7ffa7ec .note /home/test/Desktop/localization_sim/main_mix
0x00007ffff7ffa7ec 0x00007ffff7ffa828 .eh_frame_hdr /home/test/Desktop/localization_sim/main_mix
0x00007ffff7ffa828 0x00007ffff7ffa968 .eh_frame /home/test/Desktop/localization_sim/main_mix
0x00007ffff7ffa970 0x00007ffff7ffaf6a .text /home/test/Desktop/localization_sim/main_mix
0x00007ffff7ffaf6a 0x00007ffff7ffaff9 .altinstructions /home/test/Desktop/localization_sim/main_mix
0x00007ffff7ffaff9 0x00007ffff7ffb01b .altinstr_replacement /home/test/Desktop/localization_sim/main_mix
0x00007ffff7bd51c8 0x00007ffff7bd51ec .note.gnu.build-id ./libadd_debug.so
0x00007ffff7bd51f0 0x00007ffff7bd5230 .gnu.hash ./libadd_debug.so
0x00007ffff7bd5230 0x00007ffff7bd5380 .dynsym ./libadd_debug.so
0x00007ffff7bd5380 0x00007ffff7bd541c .dynstr ./libadd_debug.so
0x00007ffff7bd5420 0x00007ffff7bd54f8 .rela.dyn ./libadd_debug.so
0x00007ffff7bd54f8 0x00007ffff7bd5512 .init ./libadd_debug.so
0x00007ffff7bd5520 0x00007ffff7bd5530 .plt ./libadd_debug.so
0x00007ffff7bd5530 0x00007ffff7bd5540 .plt.got ./libadd_debug.so
0x00007ffff7bd5540 0x00007ffff7bd5666 .text ./libadd_debug.so
0x00007ffff7bd5668 0x00007ffff7bd5671 .fini ./libadd_debug.so
0x00007ffff7bd5674 0x00007ffff7bd5690 .eh_frame_hdr ./libadd_debug.so
0x00007ffff7bd5690 0x00007ffff7bd56f4 .eh_frame ./libadd_debug.so
0x00007ffff7dd5e68 0x00007ffff7dd5e70 .init_array ./libadd_debug.so
0x00007ffff7dd5e70 0x00007ffff7dd5e78 .fini_array ./libadd_debug.so
0x00007ffff7dd5e78 0x00007ffff7dd5e80 .jcr ./libadd_debug.so
0x00007ffff7dd5e80 0x00007ffff7dd5fd0 .dynamic ./libadd_debug.so
0x00007ffff7dd5fd0 0x00007ffff7dd6000 .got ./libadd_debug.so
0x00007ffff7dd6000 0x00007ffff7dd6018 .got.plt ./libadd_debug.so
0x00007ffff7dd6018 0x00007ffff7dd6020 .data ./libadd_debug.so
0x00007ffff7dd6020 0x00007ffff7dd6028 .bss ./libadd_debug.so
0x00007ffff79d31c8 0x00007ffff79d31ec .note.gnu.build-id ./libsub_debug.so
0x00007ffff79d31f0 0x00007ffff79d3230 .gnu.hash ./libsub_debug.so
0x00007ffff79d3230 0x00007ffff79d3380 .dynsym ./libsub_debug.so
0x00007ffff79d3380 0x00007ffff79d341c .dynstr ./libsub_debug.so
0x00007ffff79d3420 0x00007ffff79d34f8 .rela.dyn ./libsub_debug.so
0x00007ffff79d34f8 0x00007ffff79d3512 .init ./libsub_debug.so
0x00007ffff79d3520 0x00007ffff79d3530 .plt ./libsub_debug.so
0x00007ffff79d3530 0x00007ffff79d3540 .plt.got ./libsub_debug.so
0x00007ffff79d3540 0x00007ffff79d3666 .text ./libsub_debug.so
0x00007ffff79d3668 0x00007ffff79d3671 .fini ./libsub_debug.so
0x00007ffff79d3674 0x00007ffff79d3690 .eh_frame_hdr ./libsub_debug.so
0x00007ffff79d3690 0x00007ffff79d36f4 .eh_frame ./libsub_debug.so
0x00007ffff7bd3e68 0x00007ffff7bd3e70 .init_array ./libsub_debug.so
0x00007ffff7bd3e70 0x00007ffff7bd3e78 .fini_array ./libsub_debug.so
0x00007ffff7bd3e78 0x00007ffff7bd3e80 .jcr ./libsub_debug.so
0x00007ffff7bd3e80 0x00007ffff7bd3fd0 .dynamic ./libsub_debug.so
0x00007ffff7bd3fd0 0x00007ffff7bd4000 .got ./libsub_debug.so
0x00007ffff7bd4000 0x00007ffff7bd4018 .got.plt ./libsub_debug.so
0x00007ffff7bd4018 0x00007ffff7bd4020 .data ./libsub_debug.so
0x00007ffff7bd4020 0x00007ffff7bd4028 .bss ./libsub_debug.so
0x00007ffff7609270 0x00007ffff7609294 .note.gnu.build-id /lib/x86_64-linux-gnu/libc.so.6
0x00007ffff7609294 0x00007ffff76092b4 .note.ABI-tag /lib/x86_64-linux-gnu/libc.so.6
0x00007ffff76092b8 0x00007ffff760cd80 .gnu.hash /lib/x86_64-linux-gnu/libc.so.6
0x00007ffff760cd80 0x00007ffff7619ff8 .dynsym /lib/x86_64-linux-gnu/libc.so.6
0x00007ffff7619ff8 0x00007ffff761f9d7 .dynstr /lib/x86_64-linux-gnu/libc.so.6
0x00007ffff761f9d8 0x00007ffff7620b62 .gnu.version /lib/x86_64-linux-gnu/libc.so.6
0x00007ffff7620b68 0x00007ffff7620edc .gnu.version_d /lib/x86_64-linux-gnu/libc.so.6
0x00007ffff7620ee0 0x00007ffff7620f10 .gnu.version_r /lib/x86_64-linux-gnu/libc.so.6
0x00007ffff7620f10 0x00007ffff7628680 .rela.dyn /lib/x86_64-linux-gnu/libc.so.6
0x00007ffff7628680 0x00007ffff76287b8 .rela.plt /lib/x86_64-linux-gnu/libc.so.6
0x00007ffff76287c0 0x00007ffff76288a0 .plt /lib/x86_64-linux-gnu/libc.so.6
0x00007ffff76288a0 0x00007ffff76288b0 .plt.got /lib/x86_64-linux-gnu/libc.so.6
0x00007ffff76288b0 0x00007ffff777bb04 .text /lib/x86_64-linux-gnu/libc.so.6
0x00007ffff777bb10 0x00007ffff777e02d __libc_freeres_fn /lib/x86_64-linux-gnu/libc.so.6
0x00007ffff777e030 0x00007ffff777e2f2 __libc_thread_freeres_fn /lib/x86_64-linux-gnu/libc.so.6
0x00007ffff777e300 0x00007ffff779f650 .rodata /lib/x86_64-linux-gnu/libc.so.6
0x00007ffff779f650 0x00007ffff779f651 .stapsdt.base /lib/x86_64-linux-gnu/libc.so.6
0x00007ffff779f660 0x00007ffff779f67c .interp /lib/x86_64-linux-gnu/libc.so.6
0x00007ffff779f67c 0x00007ffff77a4b38 .eh_frame_hdr /lib/x86_64-linux-gnu/libc.so.6
0x00007ffff77a4b38 0x00007ffff77c53cc .eh_frame /lib/x86_64-linux-gnu/libc.so.6
0x00007ffff77c53cc 0x00007ffff77c580d .gcc_except_table /lib/x86_64-linux-gnu/libc.so.6
0x00007ffff77c5810 0x00007ffff77c8b10 .hash /lib/x86_64-linux-gnu/libc.so.6
0x00007ffff79c97c0 0x00007ffff79c97d0 .tdata /lib/x86_64-linux-gnu/libc.so.6
0x00007ffff79c97d0 0x00007ffff79c9838 .tbss /lib/x86_64-linux-gnu/libc.so.6
0x00007ffff79c97d0 0x00007ffff79c97e0 .init_array /lib/x86_64-linux-gnu/libc.so.6
0x00007ffff79c97e0 0x00007ffff79c98d8 __libc_subfreeres /lib/x86_64-linux-gnu/libc.so.6
0x00007ffff79c98d8 0x00007ffff79c98e0 __libc_atexit /lib/x86_64-linux-gnu/libc.so.6
0x00007ffff79c98e0 0x00007ffff79c9900 __libc_thread_subfreeres /lib/x86_64-linux-gnu/libc.so.6
0x00007ffff79c9900 0x00007ffff79ccba0 .data.rel.ro /lib/x86_64-linux-gnu/libc.so.6
0x00007ffff79ccba0 0x00007ffff79ccd80 .dynamic /lib/x86_64-linux-gnu/libc.so.6
0x00007ffff79ccd80 0x00007ffff79ccff0 .got /lib/x86_64-linux-gnu/libc.so.6
0x00007ffff79cd000 0x00007ffff79cd080 .got.plt /lib/x86_64-linux-gnu/libc.so.6
0x00007ffff79cd080 0x00007ffff79ce720 .data /lib/x86_64-linux-gnu/libc.so.6
0x00007ffff79ce720 0x00007ffff79d29a0 .bss /lib/x86_64-linux-gnu/libc.so.6
0x0000000000400238 0x0000000000400254 .interp /home/test/Desktop/localization_sim/main_mix
0x0000000000400254 0x0000000000400274 .note.ABI-tag /home/test/Desktop/localization_sim/main_mix
0x0000000000400274 0x0000000000400298 .note.gnu.build-id /home/test/Desktop/localization_sim/main_mix
0x0000000000400298 0x00000000004002d0 .gnu.hash /home/test/Desktop/localization_sim/main_mix
0x00000000004002d0 0x0000000000400408 .dynsym /home/test/Desktop/localization_sim/main_mix
0x0000000000400408 0x00000000004004e4 .dynstr /home/test/Desktop/localization_sim/main_mix
0x00000000004004e4 0x00000000004004fe .gnu.version /home/test/Desktop/localization_sim/main_mix
0x0000000000400500 0x0000000000400520 .gnu.version_r /home/test/Desktop/localization_sim/main_mix
0x0000000000400520 0x0000000000400538 .rela.dyn /home/test/Desktop/localization_sim/main_mix
0x0000000000400538 0x0000000000400580 .rela.plt /home/test/Desktop/localization_sim/main_mix
0x0000000000400580 0x000000000040059a .init /home/test/Desktop/localization_sim/main_mix
0x00000000004005a0 0x00000000004005e0 .plt /home/test/Desktop/localization_sim/main_mix
0x00000000004005e0 0x00000000004005e8 .plt.got /home/test/Desktop/localization_sim/main_mix
0x00000000004005f0 0x0000000000400782 .text /home/test/Desktop/localization_sim/main_mix
0x0000000000400784 0x000000000040078d .fini /home/test/Desktop/localization_sim/main_mix
0x0000000000400790 0x0000000000400794 .rodata /home/test/Desktop/localization_sim/main_mix
0x0000000000400794 0x00000000004007c8 .eh_frame_hdr /home/test/Desktop/localization_sim/main_mix
0x00000000004007c8 0x00000000004008bc .eh_frame /home/test/Desktop/localization_sim/main_mix
0x0000000000600df0 0x0000000000600df8 .init_array /home/test/Desktop/localization_sim/main_mix
0x0000000000600df8 0x0000000000600e00 .fini_array /home/test/Desktop/localization_sim/main_mix
0x0000000000600e00 0x0000000000600e08 .jcr /home/test/Desktop/localization_sim/main_mix
0x0000000000600e08 0x0000000000600ff8 .dynamic /home/test/Desktop/localization_sim/main_mix
0x0000000000600ff8 0x0000000000601000 .got /home/test/Desktop/localization_sim/main_mix
0x0000000000601000 0x0000000000601030 .got.plt /home/test/Desktop/localization_sim/main_mix
0x0000000000601030 0x0000000000601040 .data /home/test/Desktop/localization_sim/main_mix
0x0000000000601040 0x0000000000601048 .bss /home/test/Desktop/localization_sim/main_mix
0x00007ffff7dd71c8 0x00007ffff7dd71ec .note.gnu.build-id /lib64/ld-linux-x86-64.so.2
0x00007ffff7dd71f0 0x00007ffff7dd72b0 .hash /lib64/ld-linux-x86-64.so.2
0x00007ffff7dd72b0 0x00007ffff7dd7390 .gnu.hash /lib64/ld-linux-x86-64.so.2
0x00007ffff7dd7390 0x00007ffff7dd7648 .dynsym /lib64/ld-linux-x86-64.so.2
0x00007ffff7dd7648 0x00007ffff7dd77ef .dynstr /lib64/ld-linux-x86-64.so.2
0x00007ffff7dd77f0 0x00007ffff7dd782a .gnu.version /lib64/ld-linux-x86-64.so.2
0x00007ffff7dd7830 0x00007ffff7dd78d4 .gnu.version_d /lib64/ld-linux-x86-64.so.2
0x00007ffff7dd78d8 0x00007ffff7dd79f8 .rela.dyn /lib64/ld-linux-x86-64.so.2
0x00007ffff7dd79f8 0x00007ffff7dd7a58 .rela.plt /lib64/ld-linux-x86-64.so.2
0x00007ffff7dd7a60 0x00007ffff7dd7ab0 .plt /lib64/ld-linux-x86-64.so.2
0x00007ffff7dd7ab0 0x00007ffff7dd7ab8 .plt.got /lib64/ld-linux-x86-64.so.2
0x00007ffff7dd7ac0 0x00007ffff7df5850 .text /lib64/ld-linux-x86-64.so.2
0x00007ffff7df5860 0x00007ffff7df9920 .rodata /lib64/ld-linux-x86-64.so.2
0x00007ffff7df9920 0x00007ffff7df9921 .stapsdt.base /lib64/ld-linux-x86-64.so.2
0x00007ffff7df9924 0x00007ffff7df9f60 .eh_frame_hdr /lib64/ld-linux-x86-64.so.2
0x00007ffff7df9f60 0x00007ffff7dfc3f8 .eh_frame /lib64/ld-linux-x86-64.so.2
0x00007ffff7ffcbc0 0x00007ffff7ffce6c .data.rel.ro /lib64/ld-linux-x86-64.so.2
0x00007ffff7ffce70 0x00007ffff7ffcfe0 .dynamic /lib64/ld-linux-x86-64.so.2
0x00007ffff7ffcfe0 0x00007ffff7ffcff0 .got /lib64/ld-linux-x86-64.so.2
0x00007ffff7ffd000 0x00007ffff7ffd038 .got.plt /lib64/ld-linux-x86-64.so.2
0x00007ffff7ffd040 0x00007ffff7ffdfc0 .data /lib64/ld-linux-x86-64.so.2
0x00007ffff7ffdfc0 0x00007ffff7ffe168 .bss /lib64/ld-linux-x86-64.so.2
0x00007ffff7ffa120 0x00007ffff7ffa160 .hash /home/test/Desktop/localization_sim/main_mix
0x00007ffff7ffa160 0x00007ffff7ffa1a8 .gnu.hash /home/test/Desktop/localization_sim/main_mix
0x00007ffff7ffa1a8 0x00007ffff7ffa2b0 .dynsym /home/test/Desktop/localization_sim/main_mix
0x00007ffff7ffa2b0 0x00007ffff7ffa30e .dynstr /home/test/Desktop/localization_sim/main_mix
0x00007ffff7ffa30e 0x00007ffff7ffa324 .gnu.version /home/test/Desktop/localization_sim/main_mix
0x00007ffff7ffa328 0x00007ffff7ffa360 .gnu.version_d /home/test/Desktop/localization_sim/main_mix
0x00007ffff7ffa360 0x00007ffff7ffa470 .dynamic /home/test/Desktop/localization_sim/main_mix
0x00007ffff7ffa470 0x00007ffff7ffa7b0 .rodata /home/test/Desktop/localization_sim/main_mix
0x00007ffff7ffa7b0 0x00007ffff7ffa7ec .note /home/test/Desktop/localization_sim/main_mix
0x00007ffff7ffa7ec 0x00007ffff7ffa828 .eh_frame_hdr /home/test/Desktop/localization_sim/main_mix
0x00007ffff7ffa828 0x00007ffff7ffa968 .eh_frame /home/test/Desktop/localization_sim/main_mix
0x00007ffff7ffa970 0x00007ffff7ffaf6a .text /home/test/Desktop/localization_sim/main_mix
0x00007ffff7ffaf6a 0x00007ffff7ffaff9 .altinstructions /home/test/Desktop/localization_sim/main_mix
0x00007ffff7ffaff9 0x00007ffff7ffb01b .altinstr_replacement /home/test/Desktop/localization_sim/main_mix
0x00007ffff7bd51c8 0x00007ffff7bd51ec .note.gnu.build-id ./libadd_debug.so
0x00007ffff7bd51f0 0x00007ffff7bd5230 .gnu.hash ./libadd_debug.so
0x00007ffff7bd5230 0x00007ffff7bd5380 .dynsym ./libadd_debug.so
0x00007ffff7bd5380 0x00007ffff7bd541c .dynstr ./libadd_debug.so
0x00007ffff7bd5420 0x00007ffff7bd54f8 .rela.dyn ./libadd_debug.so
0x00007ffff7bd54f8 0x00007ffff7bd5512 .init ./libadd_debug.so
0x00007ffff7bd5520 0x00007ffff7bd5530 .plt ./libadd_debug.so
0x00007ffff7bd5530 0x00007ffff7bd5540 .plt.got ./libadd_debug.so
0x00007ffff7bd5540 0x00007ffff7bd5666 .text ./libadd_debug.so
0x00007ffff7bd5668 0x00007ffff7bd5671 .fini ./libadd_debug.so
0x00007ffff7bd5674 0x00007ffff7bd5690 .eh_frame_hdr ./libadd_debug.so
0x00007ffff7bd5690 0x00007ffff7bd56f4 .eh_frame ./libadd_debug.so
0x00007ffff7dd5e68 0x00007ffff7dd5e70 .init_array ./libadd_debug.so
0x00007ffff7dd5e70 0x00007ffff7dd5e78 .fini_array ./libadd_debug.so
0x00007ffff7dd5e78 0x00007ffff7dd5e80 .jcr ./libadd_debug.so
0x00007ffff7dd5e80 0x00007ffff7dd5fd0 .dynamic ./libadd_debug.so
0x00007ffff7dd5fd0 0x00007ffff7dd6000 .got ./libadd_debug.so
0x00007ffff7dd6000 0x00007ffff7dd6018 .got.plt ./libadd_debug.so
0x00007ffff7dd6018 0x00007ffff7dd6020 .data ./libadd_debug.so
0x00007ffff7dd6020 0x00007ffff7dd6028 .bss ./libadd_debug.so
0x00007ffff79d31c8 0x00007ffff79d31ec .note.gnu.build-id ./libsub_debug.so
0x00007ffff79d31f0 0x00007ffff79d3230 .gnu.hash ./libsub_debug.so
0x00007ffff79d3230 0x00007ffff79d3380 .dynsym ./libsub_debug.so
0x00007ffff79d3380 0x00007ffff79d341c .dynstr ./libsub_debug.so
0x00007ffff79d3420 0x00007ffff79d34f8 .rela.dyn ./libsub_debug.so
0x00007ffff79d34f8 0x00007ffff79d3512 .init ./libsub_debug.so
0x00007ffff79d3520 0x00007ffff79d3530 .plt ./libsub_debug.so
0x00007ffff79d3530 0x00007ffff79d3540 .plt.got ./libsub_debug.so
0x00007ffff79d3540 0x00007ffff79d3666 .text ./libsub_debug.so
0x00007ffff79d3668 0x00007ffff79d3671 .fini ./libsub_debug.so
0x00007ffff79d3674 0x00007ffff79d3690 .eh_frame_hdr ./libsub_debug.so
0x00007ffff79d3690 0x00007ffff79d36f4 .eh_frame ./libsub_debug.so
0x00007ffff7bd3e68 0x00007ffff7bd3e70 .init_array ./libsub_debug.so
0x00007ffff7bd3e70 0x00007ffff7bd3e78 .fini_array ./libsub_debug.so
0x00007ffff7bd3e78 0x00007ffff7bd3e80 .jcr ./libsub_debug.so
0x00007ffff7bd3e80 0x00007ffff7bd3fd0 .dynamic ./libsub_debug.so
0x00007ffff7bd3fd0 0x00007ffff7bd4000 .got ./libsub_debug.so
0x00007ffff7bd4000 0x00007ffff7bd4018 .got.plt ./libsub_debug.so
0x00007ffff7bd4018 0x00007ffff7bd4020 .data ./libsub_debug.so
0x00007ffff7bd4020 0x00007ffff7bd4028 .bss ./libsub_debug.so
0x00007ffff7609270 0x00007ffff7609294 .note.gnu.build-id /lib/x86_64-linux-gnu/libc.so.6
0x00007ffff7609294 0x00007ffff76092b4 .note.ABI-tag /lib/x86_64-linux-gnu/libc.so.6
0x00007ffff76092b8 0x00007ffff760cd80 .gnu.hash /lib/x86_64-linux-gnu/libc.so.6
0x00007ffff760cd80 0x00007ffff7619ff8 .dynsym /lib/x86_64-linux-gnu/libc.so.6
0x00007ffff7619ff8 0x00007ffff761f9d7 .dynstr /lib/x86_64-linux-gnu/libc.so.6
0x00007ffff761f9d8 0x00007ffff7620b62 .gnu.version /lib/x86_64-linux-gnu/libc.so.6
0x00007ffff7620b68 0x00007ffff7620edc .gnu.version_d /lib/x86_64-linux-gnu/libc.so.6
0x00007ffff7620ee0 0x00007ffff7620f10 .gnu.version_r /lib/x86_64-linux-gnu/libc.so.6
0x00007ffff7620f10 0x00007ffff7628680 .rela.dyn /lib/x86_64-linux-gnu/libc.so.6
0x00007ffff7628680 0x00007ffff76287b8 .rela.plt /lib/x86_64-linux-gnu/libc.so.6
0x00007ffff76287c0 0x00007ffff76288a0 .plt /lib/x86_64-linux-gnu/libc.so.6
0x00007ffff76288a0 0x00007ffff76288b0 .plt.got /lib/x86_64-linux-gnu/libc.so.6
0x00007ffff76288b0 0x00007ffff777bb04 .text /lib/x86_64-linux-gnu/libc.so.6
0x00007ffff777bb10 0x00007ffff777e02d __libc_freeres_fn /lib/x86_64-linux-gnu/libc.so.6
0x00007ffff777e030 0x00007ffff777e2f2 __libc_thread_freeres_fn /lib/x86_64-linux-gnu/libc.so.6
0x00007ffff777e300 0x00007ffff779f650 .rodata /lib/x86_64-linux-gnu/libc.so.6
0x00007ffff779f650 0x00007ffff779f651 .stapsdt.base /lib/x86_64-linux-gnu/libc.so.6
0x00007ffff779f660 0x00007ffff779f67c .interp /lib/x86_64-linux-gnu/libc.so.6
0x00007ffff779f67c 0x00007ffff77a4b38 .eh_frame_hdr /lib/x86_64-linux-gnu/libc.so.6
0x00007ffff77a4b38 0x00007ffff77c53cc .eh_frame /lib/x86_64-linux-gnu/libc.so.6
0x00007ffff77c53cc 0x00007ffff77c580d .gcc_except_table /lib/x86_64-linux-gnu/libc.so.6
0x00007ffff77c5810 0x00007ffff77c8b10 .hash /lib/x86_64-linux-gnu/libc.so.6
0x00007ffff79c97c0 0x00007ffff79c97d0 .tdata /lib/x86_64-linux-gnu/libc.so.6
0x00007ffff79c97d0 0x00007ffff79c9838 .tbss /lib/x86_64-linux-gnu/libc.so.6
0x00007ffff79c97d0 0x00007ffff79c97e0 .init_array /lib/x86_64-linux-gnu/libc.so.6
0x00007ffff79c97e0 0x00007ffff79c98d8 __libc_subfreeres /lib/x86_64-linux-gnu/libc.so.6
0x00007ffff79c98d8 0x00007ffff79c98e0 __libc_atexit /lib/x86_64-linux-gnu/libc.so.6
0x00007ffff79c98e0 0x00007ffff79c9900 __libc_thread_subfreeres /lib/x86_64-linux-gnu/libc.so.6
0x00007ffff79c9900 0x00007ffff79ccba0 .data.rel.ro /lib/x86_64-linux-gnu/libc.so.6
0x00007ffff79ccba0 0x00007ffff79ccd80 .dynamic /lib/x86_64-linux-gnu/libc.so.6
0x00007ffff79ccd80 0x00007ffff79ccff0 .got /lib/x86_64-linux-gnu/libc.so.6
0x00007ffff79cd000 0x00007ffff79cd080 .got.plt /lib/x86_64-linux-gnu/libc.so.6
0x00007ffff79cd080 0x00007ffff79ce720 .data /lib/x86_64-linux-gnu/libc.so.6
0x00007ffff79ce720 0x00007ffff79d29a0 .bss /lib/x86_64-linux-gnu/libc.so.6
或者
(gdb) info files
注：xfiles命令GEF插件扩展的命令，info files是GDB原生的命令。
输出结果中：
libadd_debug.so、libsub_debug.so等所有共享库中的sections位于进程（程序的一个运行实例）虚拟地址空间中的共享库的内存映射区域。
可执行文件main_mix中的.init、.text 和.rodata section位于进程虚拟地址空间中的只读代码段。
可执行文件main_mix中的.data和.bss section位于进程虚拟地址空间中的读/写段。
由共享库libadd_debug.so定义的全局变量g_sum位于进程虚拟地址空间中的共享库的内存映射区域，前提是只有共享库libadd_debug.so会访问该全局变量。如果可执行文件也访问该全局变量，那么g_sum会位于进程虚拟地址空间中的数据段，这一点可以通过调试得到验证。
step 5:进一步研究
如果可执行文件和共享库都调用由共享库定义的全局变量时，那么：
可执行文件是如何访问该全局变量的？
共享库是如何访问该全局变量的？与只有共享库访问该全局变量时有什么不同？
在“只有共享库访问该全局变量”、“可执行文件和共享库都调用由共享库定义的全局变量”这两种情况下，全局变量分别在进程虚拟地址空间中的位置？
注：重定位方式R_X86_64_COPY的含义：The link editor creates this relocation type for dynamic linking. Its offset member refers to a location in a writable segment. The symbol table index specifies a symbol that should exist both in the current object file and in a shared object. During execution, the dynamic linker copies data associated with the shared object's symbol to the specified by the offset.
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