可执行文件SCP传输时，可能导致库丢失原因探讨

可执行文件SCP传输时，可能导致库丢失原因探讨

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0. 问题分析

从PC传输文件到嵌入式平台有以下集中方式，当使用SSH传输文件时，发现传输可执行文件压缩包时程序解压都可以正确执行，而直接传输可执行文件后，会出现程序链接库丢失问题。

1. 简述

通过压缩包与直接传输方式，传输可执行文件 tree，比较他们的异同，压缩包方式为 A，直传为 B

2. file指令查看基本信息

注意，此时dynamically linked转变为statically linked。

# A
ELF 64-bit LSB executable, ARM aarch64, version 1 (SYSV), dynamically linked, interpreter /lib/ld-linux-aarch64.so.1, BuildID[sha1]=0c126f1b17601d33513b52c02a5e63358d912512, for GNU/Linux 3.14.0, with debug_info, not stripped

# B
ELF 64-bit LSB executable, ARM aarch64, version 1 (SYSV), statically linked, interpreter *empty*, stripped

3. ldd指令查看动态链接库连接情况

# A
linux-vdso.so.1 (0x0000ffff8a54f000)
	libc.so.6 => /lib/libc.so.6 (0x0000ffff8a3b7000)
	/lib/ld-linux-aarch64.so.1 (0x0000ffff8a521000)
# B
not a dynamic executable

4. nm指令查看符号信息

nm可以列出二进制可执行文件，动态库，静态库中的符号信息，包括符号的类型，符号名称，比如函数名，全局变量等。

# A
000000000424b24 B Dflag
0000000000424b0c B Fflag
0000000000406d04 T Ftype
0000000000424b38 B Hflag
0000000000424b28 B Jflag
0000000000424af4 B Level
0000000000424b5c B Nflag
0000000000424b30 B Qflag
0000000000424af8 B Rflag
0000000000424b74 B Xflag
0000000000423e08 d _DYNAMIC
0000000000423fd8 d _GLOBAL_OFFSET_TABLE_
000000000040fcb0 R _IO_stdin_used
0000000000413d7c r __FRAME_END__
00000000004132f8 r __GNU_EH_FRAME_HDR
0000000000424890 D __TMC_END__
0000000000426508 B __bss_end__
0000000000424890 B __bss_start
# B
nm: warning: ./tree001 has a corrupt section with a size (6d616e656c696674) larger than the file size

5. readelf指令分析可执行文件结构

如果二进制文件是ELF格式的，通过file文件可以查看文件格式.使用readelf指令可以方便分析ELF文件的结构，比如节信息，elf头文件信息。

# A
ELF Header:
Magic:   7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00 
  Class:                             ELF64
  Data:                              2's complement, little endian
  Version:                           1 (current)
  OS/ABI:                            UNIX - System V
  ABI Version:                       0
  Type:                              EXEC (Executable file)
  Machine:                           AArch64
  Version:                           0x1
  Entry point address:               0x401410
  Start of program headers:          64 (bytes into file)
  Start of section headers:          174024 (bytes into file)
  Flags:                             0x0
  Size of this header:               64 (bytes)
  Size of program headers:           56 (bytes)
  Number of program headers:         9
  Size of section headers:           64 (bytes)
  Number of section headers:         36
  Section header string table index: 35
 
 # B
  ELF Header:
  Magic:   7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00 
  Class:                             ELF64
  Data:                              2's complement, little endian
  Version:                           1 (current)
  OS/ABI:                            UNIX - System V
  ABI Version:                       0
  Type:                              EXEC (Executable file)
  Machine:                           AArch64
  Version:                           0x1
  Entry point address:               0x401410
  Start of program headers:          64 (bytes into file)
  Start of section headers:          174024 (bytes into file)
  Flags:                             0x0
  Size of this header:               64 (bytes)
  Size of program headers:           56 (bytes)
  Number of program headers:         9
  Size of section headers:           64 (bytes)
  Number of section headers:         36
  Section header string table index: 35
readelf: Warning: Section 0 has an out of range sh_link value of 1282605157
readelf: Warning: Section 0 has an out of range sh_info value of 1818588773
readelf: Warning: Section 1 has an out of range sh_link value of 1702064737

6.结论

传输可执行文件时，将文件压缩后再传输。