参考： #
可执行文件相关的命令和工具： https://linuxtools-rst.readthedocs.io/zh_CN/latest/tool/index.html
简介 #
在单片机编程中，最终得到的是一个 axf/hex/bin 格式的文件，这个文件怎么在CPU上执行的？里面的各种分段又是怎么回事呢？
文件格式区分 #
*.ELF（Executable and Linkable Format）：
https://en.wikipedia.org/wiki/Executable_and_Linkable_Format
.axf：
.bin: 从axf文件中精简出来的文件，大小远远小于axf。
.hex: 另外一种格式的bin文件。
https://www.keil.com/support/docs/1584/
.PE: portable executable，windows下的elf
.ELF执行原理： #
.ELF只是一种文件格式，具体的执行逻辑是交给执行者实现的。
- 对于STM32，执行者就是cortex-M核
- 对于Linux或者windows操作系统内核，执行者是uboot
- 对于Linux或者Windows操作系统，执行者是Linux内核或者Windows内核。
举个栗子：ELF文件的执行过程： #
1.STM32的固件： #
- STM32的固件有三种格式：axf、hex、bin。 前两种都是elf格式，最后的叫做binary格式。
- elf格式中的信息有：header、地址、代码、数据、符号表；binary格式中的信息有：代码、数据
- 因此当我们使用jflash烧录时：
- 如果是elf文件，jflash会解析此elf文件，将代码和数据烧写到elf中指定的地址
- 如果是bin文件，则要求用户手动指定地址，并将代码和数据烧写到指定地址。
2.Linux的uboot和kernel image： #
- 先通过一定的方法（根据芯片厂商指定）将uboot烧录到指定为止（flash、emmc）
- uboot再去读取并解析 kernel image，通常是zImage格式
- uboot将zImage中的代码和数据拷贝到ddr中
FPIC #
FPIC的参考资料：
stackoverflow an example of fpic https://stackoverflow.com/questions/5311515/gcc-fpic-option
这里值得一提的是，zImage的代码在编译时一定是PIC(Position Independent Code)的，即位置独立，zImage可以加载到任何位置。 PIC的实现原理是，在调用函数时，比如
b funA时，编译器会使用相对地址，例如b .+0x10这样的方法。虽然会增加一次额外的计算，降低一点点效率。
举例 #
使用readelf命令读取的keil编译之后的文件如下：
[root@iZ2zefbvkcoj7o7ledf4oqZ ~]# readelf -a MultipleDisastersRTU.axf
ELF Header:
Magic: 7f 45 4c 46 01 01 01 00 00 00 00 00 00 00 00 00
Class: ELF32
Data: 2's complement, little endian
Version: 1 (current)
OS/ABI: UNIX - System V
ABI Version: 0
Type: EXEC (Executable file)
Machine: ARM
Version: 0x1
Entry point address: 0x8020299
Start of program headers: 1203160 (bytes into file)
Start of section headers: 1203192 (bytes into file)
Flags: 0x5000002, Version5 EABI, <unknown>
Size of this header: 52 (bytes)
Size of program headers: 32 (bytes)
Number of program headers: 1
Size of section headers: 40 (bytes)
Number of section headers: 15
Section header string table index: 14
Section Headers:
[Nr] Name Type Addr Off Size ES Flg Lk Inf Al
[ 0] NULL 00000000 000000 000000 00 0 0 0
[ 1] ER_IROM1 PROGBITS 08020000 000040 03f82c 00 AX 0 0 8
[ 2] RW_IRAM2 PROGBITS 24000000 03f870 000230 00 WA 0 0 16
[ 3] RW_IRAM2 NOBITS 24002760 03faa0 0412f8 00 WA 0 0 16
[ 4] .debug_abbrev PROGBITS 00000000 03faa0 008d1f 00 0 0 1
[ 5] .debug_frame PROGBITS 00000000 0487bf 00ad1c 00 0 0 1
[ 6] .debug_info PROGBITS 00000000 0534db 046070 00 0 0 1
[ 7] .debug_line PROGBITS 00000000 09954b 03ceca 00 0 0 1
[ 8] .debug_str PROGBITS 00000000 0d6415 033bf5 00 0 0 1
[ 9] .debug_ranges PROGBITS 00000000 10a00a 0037d0 00 0 0 1
[10] .symtab SYMTAB 00000000 10d7dc 00ce00 10 11 2192 4
[11] .strtab STRTAB 00000000 11a5dc 00a894 00 0 0 1
[12] .note NOTE 00000000 124e70 00001c 00 0 0 4
[13] .comment PROGBITS 00000000 124e8c 000cc4 00 0 0 1
[14] .shstrtab STRTAB 00000000 125b50 000088 00 0 0 1
Key to Flags:
W (write), A (alloc), X (execute), M (merge), S (strings), I (info),
L (link order), O (extra OS processing required), G (group), T (TLS),
C (compressed), x (unknown), o (OS specific), E (exclude),
y (purecode), p (processor specific)
There are no section groups in this file.
Program Headers:
Type Offset VirtAddr PhysAddr FileSiz MemSiz Flg Align
LOAD 0x000040 0x08020000 0x08020000 0x3fa60 0x83288 RWE 0x10
Section to Segment mapping:
Segment Sections...
00 ER_IROM1
There is no dynamic section in this file.
There are no relocations in this file.
There are no unwind sections in this file.
Symbol table '.symtab' contains 3296 entries:
Num: Value Size Type Bind Vis Ndx Name
0: 00000000 0 NOTYPE LOCAL DEFAULT UND
1: 08020000 0 NOTYPE LOCAL DEFAULT 1 $d.realdata
2: 08020298 0 NOTYPE LOCAL DEFAULT 1 $t
3: 080202a4 0 NOTYPE LOCAL DEFAULT 1 $d
4: 080202ac 0 NOTYPE LOCAL DEFAULT 1 $t
5: 080202c8 0 NOTYPE LOCAL DEFAULT 1 $d
6: 080202d0 0 NOTYPE LOCAL DEFAULT 1 $t
7: 080203ea 0 NOTYPE LOCAL DEFAULT 1 $d
8: 08020404 0 NOTYPE LOCAL DEFAULT 1 $t
9: 0802050a 0 NOTYPE LOCAL DEFAULT 1 $d
10: 0802051c 0 NOTYPE LOCAL DEFAULT 1 $t
11: 0802069c 0 NOTYPE LOCAL DEFAULT 1 $d
12: 080206a4 0 NOTYPE LOCAL DEFAULT 1 $t
13: 0802072e 0 NOTYPE LOCAL DEFAULT 1 $d
14: 08020734 0 NOTYPE LOCAL DEFAULT 1 $t
15: 080207ba 0 NOTYPE LOCAL DEFAULT 1 $d
16: 080207c0 0 NOTYPE LOCAL DEFAULT 1 $t
17: 08020e98 0 NOTYPE LOCAL DEFAULT 1 $d
18: 08020ea4 0 NOTYPE LOCAL DEFAULT 1 $t
19: 08020ec4 0 NOTYPE LOCAL DEFAULT 1 $d
20: 08020ecc 0 NOTYPE LOCAL DEFAULT 1 $t
21: 08020fa8 0 NOTYPE LOCAL DEFAULT 1 $d
22: 08020fb4 0 NOTYPE LOCAL DEFAULT 1 $t
23: 080213b0 0 NOTYPE LOCAL DEFAULT 1 $d
24: 080213b8 0 NOTYPE LOCAL DEFAULT 1 $t
25: 080213e0 0 NOTYPE LOCAL DEFAULT 1 $d
26: 080213e4 0 NOTYPE LOCAL DEFAULT 1 $t
27: 0802173c 0 NOTYPE LOCAL DEFAULT 1 $d
28: 08021740 0 NOTYPE LOCAL DEFAULT 1 $t
29: 080219b0 0 NOTYPE LOCAL DEFAULT 1 $t.6
30: 08022c34 0 NOTYPE LOCAL DEFAULT 1 $d.11
31: 08022c38 0 NOTYPE LOCAL DEFAULT 1 $t.1
32: 08022f88 0 NOTYPE LOCAL DEFAULT 1 $d.3
33: 08022fa0 0 NOTYPE LOCAL DEFAULT 1 $t.6
34: 0802301c 0 NOTYPE LOCAL DEFAULT 1 $d.7
35: 08023020 0 NOTYPE LOCAL DEFAULT 1 $t.23
36: 08023894 0 NOTYPE LOCAL DEFAULT 1 $d.2
37: 08023898 0 NOTYPE LOCAL DEFAULT 1 $t.3
38: 080238e8 0 NOTYPE LOCAL DEFAULT 1 $d.4
39: 080238ec 0 NOTYPE LOCAL DEFAULT 1 $t.5
40: 08024014 0 NOTYPE LOCAL DEFAULT 1 $d.9
41: 08024018 0 NOTYPE LOCAL DEFAULT 1 $t.0
42: 0802a386 0 NOTYPE LOCAL DEFAULT 1 $d.7
43: 0802a38a 0 NOTYPE LOCAL DEFAULT 1 $t.8
44: 0802b130 0 NOTYPE LOCAL DEFAULT 1 $d.18
45: 0802b140 0 NOTYPE LOCAL DEFAULT 1 $t.19
46: 0802b3e0 0 NOTYPE LOCAL DEFAULT 1 $d.20
47: 0802b3f0 0 NOTYPE LOCAL DEFAULT 1 $t.21
48: 0802b690 0 NOTYPE LOCAL DEFAULT 1 $d.22
49: 0802b6a0 0 NOTYPE LOCAL DEFAULT 1 $t.14
50: 0802b6ce 0 NOTYPE LOCAL DEFAULT 1 $d.15
51: 0802b6d4 0 NOTYPE LOCAL DEFAULT 1 $t.16
52: 0802bd6c 0 NOTYPE LOCAL DEFAULT 1 $d.1
53: 0802bd72 0 NOTYPE LOCAL DEFAULT 1 $t.2
54: 0802c312 0 NOTYPE LOCAL DEFAULT 1 $d.3
55: 0802c316 0 NOTYPE LOCAL DEFAULT 1 $t.4
56: 0802c50a 0 NOTYPE LOCAL DEFAULT 1 $d.5
57: 0802c534 0 NOTYPE LOCAL DEFAULT 1 $t.6
58: 0802c5ae 0 NOTYPE LOCAL DEFAULT 1 $d.7
59: 0802c5b4 0 NOTYPE LOCAL DEFAULT 1 $t.8
60: 0802c630 0 NOTYPE LOCAL DEFAULT 1 $d.9
61: 0802c636 0 NOTYPE LOCAL DEFAULT 1 $t.10
62: 0802d198 0 NOTYPE LOCAL DEFAULT 1 $d.4
63: 0802d1ca 0 NOTYPE LOCAL DEFAULT 1 $t.5
64: 0802d47c 0 NOTYPE LOCAL DEFAULT 1 $d.6
65: 0802d490 0 NOTYPE LOCAL DEFAULT 1 $t.1
66: 0803090a 0 NOTYPE LOCAL DEFAULT 1 $d.16
67: 08030910 0 NOTYPE LOCAL DEFAULT 1 $t.17
68: 08033c24 0 NOTYPE LOCAL DEFAULT 1 $d.5
69: 08033c28 0 NOTYPE LOCAL DEFAULT 1 $t.6
70: 08033ff8 0 NOTYPE LOCAL DEFAULT 1 $d.2
3275: 2402a13c 4 OBJECT GLOBAL HIDDEN 3 rt_interrupt_to_thread
3276: 2402b144 8 OBJECT GLOBAL HIDDEN 3 rt_thread_defunct
3277: 2402b14c 64 OBJECT GLOBAL HIDDEN 3 rt_thread_priority_table
3278: 2402b18c 4 OBJECT GLOBAL HIDDEN 3 rt_thread_ready_priority_
3279: 2402b290 4 OBJECT GLOBAL HIDDEN 3 rt_thread_switch_interrup
3280: 2402e5cc 4 OBJECT GLOBAL HIDDEN 3 shell
3281: 2402e5d0 4 OBJECT GLOBAL HIDDEN 3 signal_intensity
3282: 2403366d 800 OBJECT GLOBAL HIDDEN 3 ucMCoilBuf
3283: 2403398d 200 OBJECT GLOBAL HIDDEN 3 ucMDiscInBuf
3284: 24033c74 32 OBJECT GLOBAL HIDDEN 3 update_start_event
3285: 240364ca 2 OBJECT GLOBAL HIDDEN 3 usMCoilStart
3286: 240364cc 2 OBJECT GLOBAL HIDDEN 3 usMDiscInStart
3287: 240364ce 20000 OBJECT GLOBAL HIDDEN 3 usMRegHoldBuf
3288: 2403b2ee 2 OBJECT GLOBAL HIDDEN 3 usMRegHoldStart
3289: 2403b2f0 20000 OBJECT GLOBAL HIDDEN 3 usMRegInBuf
3290: 24040110 2 OBJECT GLOBAL HIDDEN 3 usMRegInStart
3291: 240429f0 4 OBJECT GLOBAL HIDDEN 3 uwTick
3292: 24042a00 12 OBJECT GLOBAL HIDDEN 3 wdg
3293: 24042a10 4 OBJECT GLOBAL HIDDEN 3 wdg_ptr
3294: 24042a14 1 OBJECT GLOBAL HIDDEN 3 wkup_from_sleep_mode
3295: 24043a58 0 OBJECT GLOBAL HIDDEN 3 __initial_sp
No version information found in this file.
Displaying notes found in: .note
Owner Data size Description
ARM 0x0000000c Unknown note type: (0x40000000)
description data: 00 00 00 00 00 00 00 00 00 00 00 00
[root@iZ2zefbvkcoj7o7ledf4oqZ ~]# ls
参考资料： #
【RM 之一 ELF 文件、镜像（Image）文件、可执行文件、对象文件 详解】https://blog.csdn.net/ZCShouCSDN/article/details/100048461
ELF相关工具： #
