【知识科普】C语言的static究竟限制了谁?
这是一个有趣的话题,虽然说教科书给了你一些说法,但你真正能把static说清楚吗?本文将通过一个案例,给大家做一个深度的拆解分析。
注:在本文的讨论中,无明确说明时,指的都是static修饰函数,而非变量。
1 问题来源
最近的几个月一直在维护我的个人专属【嵌入式技术交流群】,平时大家都很积极在群里讨论技术问题。
就在上个星期,在群里收到一个有关static的讨论,我个人觉得挺有意思的,于是打算将其整理成文,希望能够帮助大家更好地理解和应用static这个关键字。
群里的原问题如下:
大佬们,问一个比较低智问题,static修饰的变量不是只能被当前文件所调用吗?为什么这里在其他.c文件可以调用get_board_led_opr这个函数获取board_demo_led_opr这个变量的值。
2 关于上述问题的答疑
问自己几个问题:
1.get函数返回什么地址(各种地址)语法上有约束条款吗?
2.static修饰的全局变量存放在哪里?它的地址是什么样的?
3.c语言里面要想访问任意一个地址,从语法层面上,能阻止得了吗?
提问者的回答:
(1)get_board_led_opr函数返回的是一个自定义的结构体get_board_led_opr。但是get_board_led_opr这个结构体被static修饰了。 (2)get_board_led_opr结构体放在了board_demo.c中,而调用get_board_led_opr函数是在leddrv.c中。
(3)我询问了另外一个群里面的大佬,他们说,static仅仅在编译期间有用。在运行状态是无效果的。也就是说,虽然leddrv.c无法直接使用get_board_led_opr这个结构体。但是可以利用get_board_led_opr函数,间接的获取get_board_led_opr这个结构体,因为get_board_led_opr函数和et_board_led_opr这个结构体在同一个.c文件中
-
被static修饰之后,这个变量变成了什么? -
C语言的万能指针。
3 教科书里的static
在C语言中,static关键字有两种主要的用法:静态变量和静态函数。
1. 静态变量:
静态变量是在程序运行期间一直存在的变量,其生命周期从声明处到程序结束。静态变量被存储在静态数据区,不会受到函数的调用和返回的影响,每次进入函数都会保留上一次的值。静态变量可以在函数内部或者全局作用域中声明。在函数内部声明的静态变量只能在该函数内部访问,而在全局作用域中声明的静态变量可以在整个文件中访问。静态变量的主要作用:- 维护变量的持久状态,保持值的连续性。- 限制变量的作用域,只能在函数内或者文件内访问。- 避免与同名的全局变量产生冲突。示例代码:
void func()
{
static int count = 0; // 定义一个静态变量
count++;
printf(“Count: %d\n”, count);
}
int main()
{
func(); // 输出:Count: 1
func(); // 输出:Count: 2
func(); // 输出:Count: 3
return 0;
}
2. 静态函数:
静态函数是只能在当前源文件中使用的函数,其作用于只限于声明所在的文件,无法被其他文件调用。使用static关键字修饰函数,可以实现函数的隐藏和封装。因此,静态函数的主要作用是限制函数的作用域,防止其他文件访问该函数,避免命名冲突,并且提高代码的可读性和可维护性。示例代码:
static void util_func(int value)
{
printf(“Value: %d\n”, value);
}
int main()
{
util_func(10); // 可以在当前文件中调用util_func函数
return 0;
}
总结:static关键字在C语言中的用法主要有静态变量和静态函数。静态变量用于维护变量的持久状态和限制作用域,静态函数用于限制函数的作用域和提高代码的可读性。
基本从ChatGPT的总结,可以了解清楚static的使用;不过它上面未提及到的一点是:
我们顺着这个思路来拆解跟踪一下代码里面的 static。
编写C代码(C源代码里面的static)
1main.c
2#include <stdio.h>
3static int g_count = 0;
4void func()
5{
6 static int l_count = 0; // 定义一个静态局部变量
7 l_count++;
8 g_count++;
9 printf("l_count: %d, g_count: %d\n", l_count, g_count);
10}
11static void util_func(int value) //定义一个静态函数
12{
13 printf("Value: %d\n", value);
14}
15extern void test_func(void);
16int main()
17{
18 func();//输出:l_count:1
19 func();//输出:l_count:2
20 func();//输出:l_count:3
21 util_func(10);//可以在当前文件中调用util_func函数,输出:Value: 10
22 test_func(); // 调用test.c中的函数
23 return 0;
24}
1test.c
2// 假设它们都是可以访问的
3extern int l_count;
4extern int g_count;
5extern void util_func(int value);
6void test_func(void)
7{
8#if 0
9 l_count++; // 访问l_count静态局部变量,编译报错
10 g_count++; // 访问g_count静态全局变量,编译报错
11 util_func(100); // 调用main.c中的static函数,编译报错
12#endif
13}
当test_func中的if-0打开后,根据我们上面的理论分析,肯定是编译不过的,如下:
1test_static$ gcc -o test *.c
2/usr/bin/ld: /tmp/ccawkyDR.o: in function `test_func':
3test.c:(.text+0xa): undefined reference to `l_count'
4/usr/bin/ld: test.c:(.text+0x13): undefined reference to `l_count'
5/usr/bin/ld: test.c:(.text+0x19): undefined reference to `g_count'
6/usr/bin/ld: test.c:(.text+0x22): undefined reference to `g_count'
7/usr/bin/ld: test.c:(.text+0x2c): undefined reference to `util_func'
8collect2: error: ld returned 1 exit status
像这种就是很明显的找不到变量或函数的实现体,从而出现找不到引用的 链接 错误。
去掉这些引用后(if-0)打开,即可编译成功,且能够正常运行。
1test_static$ gcc -o test *.c
2test_static$ ./test
3l_count: 1, g_count: 1
4l_count: 2, g_count: 2
5l_count: 3, g_count: 3
6Value: 10
分步拆解1:先看预处理后static的情况
使用的命令下:gcc -c -o main.o main.c -save-temps=obj
这时候我们可以看到 main.i main.s main.o 这几个文件。
先看main.i 的内容:
1忽略前面对头文件内容的搬运
2# 873 "/usr/include/stdio.h" 3 4
3# 2 "main.c" 2
4# 3 "main.c"
5static int g_count = 0;
6void func()
7{
8 static int l_count = 0;
9 l_count++;
10 g_count++;
11 printf("l_count: %d, g_count: %d\n", l_count, g_count);
12}
13static void util_func(int value)
14{
15 printf("Value: %d\n", value);
16}
17extern void test_func(void);
18int main()
19{
20 func();
21 func();
22 func();
23 util_func(10);
24 test_func();
25 return 0;
从上基本可以看到,static还是在的,并且整一个预处理后的代码,基本保留了源代码的样子(原因是我们并没有使用类似宏定义的内容)。
拆解第2步:看看汇编文件有没有static的影子
这时候我们要查看的是 main.s 文件:
1test_static$ cat main.s
2 .file "main.c"
3 .text
4 .local g_count
5 .comm g_count,4,4
6 .section .rodata
7.LC0:
8 .string "l_count: %d, g_count: %d\n"
9 .text
10 .globl func
11 .type func, @function
12func:
13.LFB0:
14 .cfi_startproc
15 endbr64
16 pushq %rbp
17 .cfi_def_cfa_offset 16
18 .cfi_offset 6, -16
19 movq %rsp, %rbp
20 .cfi_def_cfa_register 6
21 movl l_count.2316(%rip), %eax
22 addl $1, %eax
23 movl %eax, l_count.2316(%rip)
24 movl g_count(%rip), %eax
25 addl $1, %eax
26 movl %eax, g_count(%rip)
27 movl g_count(%rip), %edx
28 movl l_count.2316(%rip), %eax
29 movl %eax, %esi
30 leaq .LC0(%rip), %rdi
31 movl $0, %eax
32 call printf@PLT
33 nop
34 popq %rbp
35 .cfi_def_cfa 7, 8
36 ret
37 .cfi_endproc
38.LFE0:
39 .size func, .-func
40 .section .rodata
41.LC1:
42 .string "Value: %d\n"
43 .text
44 .type util_func, @function
45util_func:
46.LFB1:
47 .cfi_startproc
48 endbr64
49 pushq %rbp
50 .cfi_def_cfa_offset 16
51 .cfi_offset 6, -16
52 movq %rsp, %rbp
53 .cfi_def_cfa_register 6
54 subq $16, %rsp
55 movl %edi, -4(%rbp)
56 movl -4(%rbp), %eax
57 movl %eax, %esi
58 leaq .LC1(%rip), %rdi
59 movl $0, %eax
60 call printf@PLT
61 nop
62 leave
63 .cfi_def_cfa 7, 8
64 ret
65 .cfi_endproc
66.LFE1:
67 .size util_func, .-util_func
68 .globl main
69 .type main, @function
70main:
71.LFB2:
72 .cfi_startproc
73 endbr64
74 pushq %rbp
75 .cfi_def_cfa_offset 16
76 .cfi_offset 6, -16
77 movq %rsp, %rbp
78 .cfi_def_cfa_register 6
79 movl $0, %eax
80 call func
81 movl $0, %eax
82 call func
83 movl $0, %eax
84 call func
85 movl $10, %edi
86 call util_func
87 call test_func@PLT
88 movl $0, %eax
89 popq %rbp
90 .cfi_def_cfa 7, 8
91 ret
92 .cfi_endproc
93.LFE2:
94 .size main, .-main
95 .local l_count.2316
96 .comm l_count.2316,4,4
97 .ident "GCC: (Ubuntu 9.4.0-1ubuntu1~20.04.1) 9.4.0"
98 .section .note.GNU-stack,"",@progbits
99 .section .note.gnu.property,"a"
100 .align 8
101 .long 1f - 0f
102 .long 4f - 1f
103 .long 5
1040:
105 .string "GNU"
1061:
107 .align 8
108 .long 0xc0000002
109 .long 3f - 2f
1102:
111 .long 0x3
1123:
113 .align 8
1144:
初一打开,可能有种不太认识的感觉,没关系,我们先找到我们能认识的东西。
先找到被static修饰过的内容(静态全局变量、静态局部变量、静态函数)。
1)静态全局变量g_count:
1 .file "main.c"
2 .text
3 .local g_count
4 .comm g_count,4,4
5 .section .rodata
2)静态局部变量l_count:
1.LFE2:
2 .size main, .-main
3 .local l_count.2316
4 .comm l_count.2316,4,4
3)静态函数util_func:
1 .string "Value: %d\n"
2 .text
3 .type util_func, @function
4util_func:
5.LFB1:
6 .cfi_startproc
7 endbr64
8 pushq %rbp
9 .cfi_def_cfa_offset 16
10 .cfi_offset 6, -16
11 movq %rsp, %rbp
12 .cfi_def_cfa_register 6
13 subq $16, %rsp
14 movl %edi, -4(%rbp)
15 movl -4(%rbp), %eax
16 movl %eax, %esi
17 leaq .LC1(%rip), %rdi
18 movl $0, %eax
19 call printf@PLT
20 nop
21 leave
22 .cfi_def_cfa 7, 8
23 ret
24 .cfi_endproc
由于我们只是对main.c进行汇编,所以看不出全貌,但是能够确认的是,在汇编文件中,static已经消失了,换句话说,接下来就没static啥事情了,而是转为其他信息了。我们接着往下拆解。
拆解第3步:obj文件里面确认没有static的要素吗?
我们看下main.o文件,由于它不是可读文件,所以得用其他指令分析下:
1test_static$ readelf -a main.o
2ELF Header:
3 Magic: 7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00
4 Class: ELF64
5 Data: 2's complement, little endian
6 Version: 1 (current)
7 OS/ABI: UNIX - System V
8 ABI Version: 0
9 Type: REL (Relocatable file)
10 Machine: Advanced Micro Devices X86-64
11 Version: 0x1
12 Entry point address: 0x0
13 Start of program headers: 0 (bytes into file)
14 Start of section headers: 1520 (bytes into file)
15 Flags: 0x0
16 Size of this header: 64 (bytes)
17 Size of program headers: 0 (bytes)
18 Number of program headers: 0
19 Size of section headers: 64 (bytes)
20 Number of section headers: 14
21 Section header string table index: 13
22Section Headers:
23 [Nr] Name Type Address Offset
24 Size EntSize Flags Link Info Align
25 [ 0] NULL 0000000000000000 00000000
26 0000000000000000 0000000000000000 0 0 0
27 [ 1] .text PROGBITS 0000000000000000 00000040
28 00000000000000ac 0000000000000000 AX 0 0 1
29 [ 2] .rela.text RELA 0000000000000000 000003e0
30 0000000000000150 0000000000000018 I 11 1 8
31 [ 3] .data PROGBITS 0000000000000000 000000ec
32 0000000000000000 0000000000000000 WA 0 0 1
33 [ 4] .bss NOBITS 0000000000000000 000000ec
34 0000000000000008 0000000000000000 WA 0 0 4
35 [ 5] .rodata PROGBITS 0000000000000000 000000ec
36 0000000000000025 0000000000000000 A 0 0 1
37 [ 6] .comment PROGBITS 0000000000000000 00000111
38 000000000000002c 0000000000000001 MS 0 0 1
39 [ 7] .note.GNU-stack PROGBITS 0000000000000000 0000013d
40 0000000000000000 0000000000000000 0 0 1
41 [ 8] .note.gnu.propert NOTE 0000000000000000 00000140
42 0000000000000020 0000000000000000 A 0 0 8
43 [ 9] .eh_frame PROGBITS 0000000000000000 00000160
44 0000000000000078 0000000000000000 A 0 0 8
45 [10] .rela.eh_frame RELA 0000000000000000 00000530
46 0000000000000048 0000000000000018 I 11 9 8
47 [11] .symtab SYMTAB 0000000000000000 000001d8
48 00000000000001b0 0000000000000018 12 13 8
49 [12] .strtab STRTAB 0000000000000000 00000388
50 0000000000000053 0000000000000000 0 0 1
51 [13] .shstrtab STRTAB 0000000000000000 00000578
52 0000000000000074 0000000000000000 0 0 1
53Key to Flags:
54 W (write), A (alloc), X (execute), M (merge), S (strings), I (info),
55 L (link order), O (extra OS processing required), G (group), T (TLS),
56 C (compressed), x (unknown), o (OS specific), E (exclude),
57 l (large), p (processor specific)
58There are no section groups in this file.
59There are no program headers in this file.
60There is no dynamic section in this file.
61Relocation section '.rela.text' at offset 0x3e0 contains 14 entries:
62 Offset Info Type Sym. Value Sym. Name + Addend
6300000000000a 000400000002 R_X86_64_PC32 0000000000000000 .bss + 0
64000000000013 000400000002 R_X86_64_PC32 0000000000000000 .bss + 0
65000000000019 000400000002 R_X86_64_PC32 0000000000000000 .bss - 4
66000000000022 000400000002 R_X86_64_PC32 0000000000000000 .bss - 4
67000000000028 000400000002 R_X86_64_PC32 0000000000000000 .bss - 4
6800000000002e 000400000002 R_X86_64_PC32 0000000000000000 .bss + 0
69000000000037 000600000002 R_X86_64_PC32 0000000000000000 .rodata - 4
70000000000041 000f00000004 R_X86_64_PLT32 0000000000000000 printf - 4
7100000000005f 000600000002 R_X86_64_PC32 0000000000000000 .rodata + 16
72000000000069 000f00000004 R_X86_64_PLT32 0000000000000000 printf - 4
7300000000007e 000d00000004 R_X86_64_PLT32 0000000000000000 func - 4
74000000000088 000d00000004 R_X86_64_PLT32 0000000000000000 func - 4
75000000000092 000d00000004 R_X86_64_PLT32 0000000000000000 func - 4
760000000000a1 001100000004 R_X86_64_PLT32 0000000000000000 test_func - 4
77Relocation section '.rela.eh_frame' at offset 0x530 contains 3 entries:
78 Offset Info Type Sym. Value Sym. Name + Addend
79000000000020 000200000002 R_X86_64_PC32 0000000000000000 .text + 0
80000000000040 000200000002 R_X86_64_PC32 0000000000000000 .text + 48
81000000000060 000200000002 R_X86_64_PC32 0000000000000000 .text + 70
82The decoding of unwind sections for machine type Advanced Micro Devices X86-64 is not currently supported.
83Symbol table '.symtab' contains 18 entries:
84 Num: Value Size Type Bind Vis Ndx Name
85 0: 0000000000000000 0 NOTYPE LOCAL DEFAULT UND
86 1: 0000000000000000 0 FILE LOCAL DEFAULT ABS main.c
87 2: 0000000000000000 0 SECTION LOCAL DEFAULT 1
88 3: 0000000000000000 0 SECTION LOCAL DEFAULT 3
89 4: 0000000000000000 0 SECTION LOCAL DEFAULT 4
90 5: 0000000000000000 4 OBJECT LOCAL DEFAULT 4 g_count
91 6: 0000000000000000 0 SECTION LOCAL DEFAULT 5
92 7: 0000000000000004 4 OBJECT LOCAL DEFAULT 4 l_count.2316
93 8: 0000000000000048 40 FUNC LOCAL DEFAULT 1 util_func
94 9: 0000000000000000 0 SECTION LOCAL DEFAULT 7
95 10: 0000000000000000 0 SECTION LOCAL DEFAULT 8
96 11: 0000000000000000 0 SECTION LOCAL DEFAULT 9
97 12: 0000000000000000 0 SECTION LOCAL DEFAULT 6
98 13: 0000000000000000 72 FUNC GLOBAL DEFAULT 1 func
99 14: 0000000000000000 0 NOTYPE GLOBAL DEFAULT UND _GLOBAL_OFFSET_TABLE_
100 15: 0000000000000000 0 NOTYPE GLOBAL DEFAULT UND printf
101 16: 0000000000000070 60 FUNC GLOBAL DEFAULT 1 main
102 17: 0000000000000000 0 NOTYPE GLOBAL DEFAULT UND test_func
103No version information found in this file.
104Displaying notes found in: .note.gnu.property
105 Owner Data size Description
106 GNU 0x00000010 NT_GNU_PROPERTY_TYPE_0
107 Properties: x86 feature: IBT, SHSTK
108recan@ubuntu:~/win_share_workspace/test_share/test_static$
1 5: 0000000000000000 4 OBJECT LOCAL DEFAULT 4 g_count
2 6: 0000000000000000 0 SECTION LOCAL DEFAULT 5
3 7: 0000000000000004 4 OBJECT LOCAL DEFAULT 4 l_count.2316
4 8: 0000000000000048 40 FUNC LOCAL DEFAULT 1 util_func
究竟这两者修饰有啥区别,会产生什么影响呢?我们接着往下拆解。
拆解第4步:链接后的可执行文件反汇编
前面也说到了,由于我们都只看到 main这个C文件相关 预处理、汇编、obj内容,而没有看到整个可执行文件的全貌。
执行反汇编看看:
1test_static$ objdump -l -d -x -s -S test
2test: file format elf64-x86-64
3test
4architecture: i386:x86-64, flags 0x00000150:
5HAS_SYMS, DYNAMIC, D_PAGED
6start address 0x0000000000001060
7Program Header:
8 PHDR off 0x0000000000000040 vaddr 0x0000000000000040 paddr 0x0000000000000040 align 2**3
9 filesz 0x00000000000002d8 memsz 0x00000000000002d8 flags r--
10 INTERP off 0x0000000000000318 vaddr 0x0000000000000318 paddr 0x0000000000000318 align 2**0
11 filesz 0x000000000000001c memsz 0x000000000000001c flags r--
12 LOAD off 0x0000000000000000 vaddr 0x0000000000000000 paddr 0x0000000000000000 align 2**12
13 filesz 0x0000000000000600 memsz 0x0000000000000600 flags r--
14 LOAD off 0x0000000000001000 vaddr 0x0000000000001000 paddr 0x0000000000001000 align 2**12
15 filesz 0x0000000000000285 memsz 0x0000000000000285 flags r-x
16 LOAD off 0x0000000000002000 vaddr 0x0000000000002000 paddr 0x0000000000002000 align 2**12
17 filesz 0x00000000000001f0 memsz 0x00000000000001f0 flags r--
18 LOAD off 0x0000000000002db8 vaddr 0x0000000000003db8 paddr 0x0000000000003db8 align 2**12
19 filesz 0x0000000000000258 memsz 0x0000000000000268 flags rw-
20 DYNAMIC off 0x0000000000002dc8 vaddr 0x0000000000003dc8 paddr 0x0000000000003dc8 align 2**3
21 filesz 0x00000000000001f0 memsz 0x00000000000001f0 flags rw-
22 NOTE off 0x0000000000000338 vaddr 0x0000000000000338 paddr 0x0000000000000338 align 2**3
23 filesz 0x0000000000000020 memsz 0x0000000000000020 flags r--
24 NOTE off 0x0000000000000358 vaddr 0x0000000000000358 paddr 0x0000000000000358 align 2**2
25 filesz 0x0000000000000044 memsz 0x0000000000000044 flags r--
260x6474e553 off 0x0000000000000338 vaddr 0x0000000000000338 paddr 0x0000000000000338 align 2**3
27 filesz 0x0000000000000020 memsz 0x0000000000000020 flags r--
28EH_FRAME off 0x000000000000202c vaddr 0x000000000000202c paddr 0x000000000000202c align 2**2
29 filesz 0x000000000000005c memsz 0x000000000000005c flags r--
30 STACK off 0x0000000000000000 vaddr 0x0000000000000000 paddr 0x0000000000000000 align 2**4
31 filesz 0x0000000000000000 memsz 0x0000000000000000 flags rw-
32 RELRO off 0x0000000000002db8 vaddr 0x0000000000003db8 paddr 0x0000000000003db8 align 2**0
33 filesz 0x0000000000000248 memsz 0x0000000000000248 flags r--
34Dynamic Section:
35 NEEDED libc.so.6
36 INIT 0x0000000000001000
37 FINI 0x0000000000001278
38 INIT_ARRAY 0x0000000000003db8
39 INIT_ARRAYSZ 0x0000000000000008
40 FINI_ARRAY 0x0000000000003dc0
41 FINI_ARRAYSZ 0x0000000000000008
42 GNU_HASH 0x00000000000003a0
43 STRTAB 0x0000000000000470
44 SYMTAB 0x00000000000003c8
45 STRSZ 0x0000000000000084
46 SYMENT 0x0000000000000018
47 DEBUG 0x0000000000000000
48 PLTGOT 0x0000000000003fb8
49 PLTRELSZ 0x0000000000000018
50 PLTREL 0x0000000000000007
51 JMPREL 0x00000000000005e8
52 RELA 0x0000000000000528
53 RELASZ 0x00000000000000c0
54 RELAENT 0x0000000000000018
55 FLAGS 0x0000000000000008
56 FLAGS_1 0x0000000008000001
57 VERNEED 0x0000000000000508
58 VERNEEDNUM 0x0000000000000001
59 VERSYM 0x00000000000004f4
60 RELACOUNT 0x0000000000000003
61Version References:
62 required from libc.so.6:
63 0x09691a75 0x00 02 GLIBC_2.2.5
64Sections:
65Idx Name Size VMA LMA File off Algn
66 0 .interp 0000001c 0000000000000318 0000000000000318 00000318 2**0
67 CONTENTS, ALLOC, LOAD, READONLY, DATA
68 1 .note.gnu.property 00000020 0000000000000338 0000000000000338 00000338 2**3
69 CONTENTS, ALLOC, LOAD, READONLY, DATA
70 2 .note.gnu.build-id 00000024 0000000000000358 0000000000000358 00000358 2**2
71 CONTENTS, ALLOC, LOAD, READONLY, DATA
72 3 .note.ABI-tag 00000020 000000000000037c 000000000000037c 0000037c 2**2
73 CONTENTS, ALLOC, LOAD, READONLY, DATA
74 4 .gnu.hash 00000024 00000000000003a0 00000000000003a0 000003a0 2**3
75 CONTENTS, ALLOC, LOAD, READONLY, DATA
76 5 .dynsym 000000a8 00000000000003c8 00000000000003c8 000003c8 2**3
77 CONTENTS, ALLOC, LOAD, READONLY, DATA
78 6 .dynstr 00000084 0000000000000470 0000000000000470 00000470 2**0
79 CONTENTS, ALLOC, LOAD, READONLY, DATA
80 7 .gnu.version 0000000e 00000000000004f4 00000000000004f4 000004f4 2**1
81 CONTENTS, ALLOC, LOAD, READONLY, DATA
82 8 .gnu.version_r 00000020 0000000000000508 0000000000000508 00000508 2**3
83 CONTENTS, ALLOC, LOAD, READONLY, DATA
84 9 .rela.dyn 000000c0 0000000000000528 0000000000000528 00000528 2**3
85 CONTENTS, ALLOC, LOAD, READONLY, DATA
86 10 .rela.plt 00000018 00000000000005e8 00000000000005e8 000005e8 2**3
87 CONTENTS, ALLOC, LOAD, READONLY, DATA
88 11 .init 0000001b 0000000000001000 0000000000001000 00001000 2**2
89 CONTENTS, ALLOC, LOAD, READONLY, CODE
90 12 .plt 00000020 0000000000001020 0000000000001020 00001020 2**4
91 CONTENTS, ALLOC, LOAD, READONLY, CODE
92 13 .plt.got 00000010 0000000000001040 0000000000001040 00001040 2**4
93 CONTENTS, ALLOC, LOAD, READONLY, CODE
94 14 .plt.sec 00000010 0000000000001050 0000000000001050 00001050 2**4
95 CONTENTS, ALLOC, LOAD, READONLY, CODE
96 15 .text 00000215 0000000000001060 0000000000001060 00001060 2**4
97 CONTENTS, ALLOC, LOAD, READONLY, CODE
98 16 .fini 0000000d 0000000000001278 0000000000001278 00001278 2**2
99 CONTENTS, ALLOC, LOAD, READONLY, CODE
100 17 .rodata 00000029 0000000000002000 0000000000002000 00002000 2**2
101 CONTENTS, ALLOC, LOAD, READONLY, DATA
102 18 .eh_frame_hdr 0000005c 000000000000202c 000000000000202c 0000202c 2**2
103 CONTENTS, ALLOC, LOAD, READONLY, DATA
104 19 .eh_frame 00000168 0000000000002088 0000000000002088 00002088 2**3
105 CONTENTS, ALLOC, LOAD, READONLY, DATA
106 20 .init_array 00000008 0000000000003db8 0000000000003db8 00002db8 2**3
107 CONTENTS, ALLOC, LOAD, DATA
108 21 .fini_array 00000008 0000000000003dc0 0000000000003dc0 00002dc0 2**3
109 CONTENTS, ALLOC, LOAD, DATA
110 22 .dynamic 000001f0 0000000000003dc8 0000000000003dc8 00002dc8 2**3
111 CONTENTS, ALLOC, LOAD, DATA
112 23 .got 00000048 0000000000003fb8 0000000000003fb8 00002fb8 2**3
113 CONTENTS, ALLOC, LOAD, DATA
114 24 .data 00000010 0000000000004000 0000000000004000 00003000 2**3
115 CONTENTS, ALLOC, LOAD, DATA
116 25 .bss 00000010 0000000000004010 0000000000004010 00003010 2**2
117 ALLOC
118 26 .comment 0000002b 0000000000000000 0000000000000000 00003010 2**0
119 CONTENTS, READONLY
120SYMBOL TABLE:
1210000000000000318 l d .interp 0000000000000000 .interp
1220000000000000338 l d .note.gnu.property 0000000000000000 .note.gnu.property
1230000000000000358 l d .note.gnu.build-id 0000000000000000 .note.gnu.build-id
124000000000000037c l d .note.ABI-tag 0000000000000000 .note.ABI-tag
12500000000000003a0 l d .gnu.hash 0000000000000000 .gnu.hash
12600000000000003c8 l d .dynsym 0000000000000000 .dynsym
1270000000000000470 l d .dynstr 0000000000000000 .dynstr
12800000000000004f4 l d .gnu.version 0000000000000000 .gnu.version
1290000000000000508 l d .gnu.version_r 0000000000000000 .gnu.version_r
1300000000000000528 l d .rela.dyn 0000000000000000 .rela.dyn
13100000000000005e8 l d .rela.plt 0000000000000000 .rela.plt
1320000000000001000 l d .init 0000000000000000 .init
1330000000000001020 l d .plt 0000000000000000 .plt
1340000000000001040 l d .plt.got 0000000000000000 .plt.got
1350000000000001050 l d .plt.sec 0000000000000000 .plt.sec
1360000000000001060 l d .text 0000000000000000 .text
1370000000000001278 l d .fini 0000000000000000 .fini
1380000000000002000 l d .rodata 0000000000000000 .rodata
139000000000000202c l d .eh_frame_hdr 0000000000000000 .eh_frame_hdr
1400000000000002088 l d .eh_frame 0000000000000000 .eh_frame
1410000000000003db8 l d .init_array 0000000000000000 .init_array
1420000000000003dc0 l d .fini_array 0000000000000000 .fini_array
1430000000000003dc8 l d .dynamic 0000000000000000 .dynamic
1440000000000003fb8 l d .got 0000000000000000 .got
1450000000000004000 l d .data 0000000000000000 .data
1460000000000004010 l d .bss 0000000000000000 .bss
1470000000000000000 l d .comment 0000000000000000 .comment
1480000000000000000 l df *ABS* 0000000000000000 crtstuff.c
1490000000000001090 l F .text 0000000000000000 deregister_tm_clones
15000000000000010c0 l F .text 0000000000000000 register_tm_clones
1510000000000001100 l F .text 0000000000000000 __do_global_dtors_aux
1520000000000004010 l O .bss 0000000000000001 completed.8061
1530000000000003dc0 l O .fini_array 0000000000000000 __do_global_dtors_aux_fini_array_entry
1540000000000001140 l F .text 0000000000000000 frame_dummy
1550000000000003db8 l O .init_array 0000000000000000 __frame_dummy_init_array_entry
1560000000000000000 l df *ABS* 0000000000000000 main.c
1570000000000004014 l O .bss 0000000000000004 g_count
1580000000000004018 l O .bss 0000000000000004 l_count.2316
1590000000000001191 l F .text 0000000000000028 util_func
1600000000000000000 l df *ABS* 0000000000000000 test.c
1610000000000000000 l df *ABS* 0000000000000000 crtstuff.c
16200000000000021ec l O .eh_frame 0000000000000000 __FRAME_END__
1630000000000000000 l df *ABS* 0000000000000000
1640000000000003dc0 l .init_array 0000000000000000 __init_array_end
1650000000000003dc8 l O .dynamic 0000000000000000 _DYNAMIC
1660000000000003db8 l .init_array 0000000000000000 __init_array_start
167000000000000202c l .eh_frame_hdr 0000000000000000 __GNU_EH_FRAME_HDR
1680000000000003fb8 l O .got 0000000000000000 _GLOBAL_OFFSET_TABLE_
1690000000000001000 l F .init 0000000000000000 _init
1700000000000001270 g F .text 0000000000000005 __libc_csu_fini
1710000000000000000 w *UND* 0000000000000000 _ITM_deregisterTMCloneTable
1720000000000004000 w .data 0000000000000000 data_start
1730000000000004010 g .data 0000000000000000 _edata
1740000000000001278 g F .fini 0000000000000000 .hidden _fini
1750000000000000000 F *UND* 0000000000000000 printf@@GLIBC_2.2.5
17600000000000011f5 g F .text 000000000000000b test_func
1770000000000000000 F *UND* 0000000000000000 __libc_start_main@@GLIBC_2.2.5
1780000000000004000 g .data 0000000000000000 __data_start
1790000000000000000 w *UND* 0000000000000000 __gmon_start__
1800000000000004008 g O .data 0000000000000000 .hidden __dso_handle
1810000000000002000 g O .rodata 0000000000000004 _IO_stdin_used
1820000000000001149 g F .text 0000000000000048 func
1830000000000001200 g F .text 0000000000000065 __libc_csu_init
1840000000000004020 g .bss 0000000000000000 _end
1850000000000001060 g F .text 000000000000002f _start
1860000000000004010 g .bss 0000000000000000 __bss_start
18700000000000011b9 g F .text 000000000000003c main
1880000000000004010 g O .data 0000000000000000 .hidden __TMC_END__
1890000000000000000 w *UND* 0000000000000000 _ITM_registerTMCloneTable
1900000000000000000 w F *UND* 0000000000000000 __cxa_finalize@@GLIBC_2.2.5
191Contents of section .interp:
192 0318 2f6c6962 36342f6c 642d6c69 6e75782d /lib64/ld-linux-
193 0328 7838362d 36342e73 6f2e3200 x86-64.so.2.
194 省略了一些无关紧要的内容
195Contents of section .data:
196 4000 00000000 00000000 08400000 00000000 .........@......
197Contents of section .comment:
198 0000 4743433a 20285562 756e7475 20392e34 GCC: (Ubuntu 9.4
199 0010 2e302d31 7562756e 7475317e 32302e30 .0-1ubuntu1~20.0
200 0020 342e3129 20392e34 2e3000 4.1) 9.4.0.
201Disassembly of section .init:
2020000000000001000 <_init>:
203_init():
204 1000: f3 0f 1e fa endbr64
205 1004: 48 83 ec 08 sub $0x8,%rsp
206 1008: 48 8b 05 d9 2f 00 00 mov 0x2fd9(%rip),%rax # 3fe8 <__gmon_start__>
207 100f: 48 85 c0 test %rax,%rax
208 1012: 74 02 je 1016 <_init+0x16>
209 1014: ff d0 callq *%rax
210 1016: 48 83 c4 08 add $0x8,%rsp
211 101a: c3 retq
212Disassembly of section .plt:
2130000000000001020 <.plt>:
214 1020: ff 35 9a 2f 00 00 pushq 0x2f9a(%rip) # 3fc0 <_GLOBAL_OFFSET_TABLE_+0x8>
215 1026: f2 ff 25 9b 2f 00 00 bnd jmpq *0x2f9b(%rip) # 3fc8 <_GLOBAL_OFFSET_TABLE_+0x10>
216 102d: 0f 1f 00 nopl (%rax)
217 1030: f3 0f 1e fa endbr64
218 1034: 68 00 00 00 00 pushq $0x0
219 1039: f2 e9 e1 ff ff ff bnd jmpq 1020 <.plt>
220 103f: 90 nop
221Disassembly of section .plt.got:
2220000000000001040 <__cxa_finalize@plt>:
223 1040: f3 0f 1e fa endbr64
224 1044: f2 ff 25 ad 2f 00 00 bnd jmpq *0x2fad(%rip) # 3ff8 <__cxa_finalize@GLIBC_2.2.5>
225 104b: 0f 1f 44 00 00 nopl 0x0(%rax,%rax,1)
226Disassembly of section .plt.sec:
2270000000000001050 <printf@plt>:
228 1050: f3 0f 1e fa endbr64
229 1054: f2 ff 25 75 2f 00 00 bnd jmpq *0x2f75(%rip) # 3fd0 <printf@GLIBC_2.2.5>
230 105b: 0f 1f 44 00 00 nopl 0x0(%rax,%rax,1)
231Disassembly of section .text:
2320000000000001060 <_start>:
233_start():
234 1060: f3 0f 1e fa endbr64
235 1064: 31 ed xor %ebp,%ebp
236 1066: 49 89 d1 mov %rdx,%r9
237 1069: 5e pop %rsi
238 106a: 48 89 e2 mov %rsp,%rdx
239 106d: 48 83 e4 f0 and $0xfffffffffffffff0,%rsp
240 1071: 50 push %rax
241 1072: 54 push %rsp
242 1073: 4c 8d 05 f6 01 00 00 lea 0x1f6(%rip),%r8 # 1270 <__libc_csu_fini>
243 107a: 48 8d 0d 7f 01 00 00 lea 0x17f(%rip),%rcx # 1200 <__libc_csu_init>
244 1081: 48 8d 3d 31 01 00 00 lea 0x131(%rip),%rdi # 11b9 <main>
245 1088: ff 15 52 2f 00 00 callq *0x2f52(%rip) # 3fe0 <__libc_start_main@GLIBC_2.2.5>
246 108e: f4 hlt
247 108f: 90 nop
2480000000000001090 <deregister_tm_clones>:
249deregister_tm_clones():
250 1090: 48 8d 3d 79 2f 00 00 lea 0x2f79(%rip),%rdi # 4010 <__TMC_END__>
251 1097: 48 8d 05 72 2f 00 00 lea 0x2f72(%rip),%rax # 4010 <__TMC_END__>
252 109e: 48 39 f8 cmp %rdi,%rax
253 10a1: 74 15 je 10b8 <deregister_tm_clones+0x28>
254 10a3: 48 8b 05 2e 2f 00 00 mov 0x2f2e(%rip),%rax # 3fd8 <_ITM_deregisterTMCloneTable>
255 10aa: 48 85 c0 test %rax,%rax
256 10ad: 74 09 je 10b8 <deregister_tm_clones+0x28>
257 10af: ff e0 jmpq *%rax
258 10b1: 0f 1f 80 00 00 00 00 nopl 0x0(%rax)
259 10b8: c3 retq
260 10b9: 0f 1f 80 00 00 00 00 nopl 0x0(%rax)
26100000000000010c0 <register_tm_clones>:
262register_tm_clones():
263 10c0: 48 8d 3d 49 2f 00 00 lea 0x2f49(%rip),%rdi # 4010 <__TMC_END__>
264 10c7: 48 8d 35 42 2f 00 00 lea 0x2f42(%rip),%rsi # 4010 <__TMC_END__>
265 10ce: 48 29 fe sub %rdi,%rsi
266 10d1: 48 89 f0 mov %rsi,%rax
267 10d4: 48 c1 ee 3f shr $0x3f,%rsi
268 10d8: 48 c1 f8 03 sar $0x3,%rax
269 10dc: 48 01 c6 add %rax,%rsi
270 10df: 48 d1 fe sar %rsi
271 10e2: 74 14 je 10f8 <register_tm_clones+0x38>
272 10e4: 48 8b 05 05 2f 00 00 mov 0x2f05(%rip),%rax # 3ff0 <_ITM_registerTMCloneTable>
273 10eb: 48 85 c0 test %rax,%rax
274 10ee: 74 08 je 10f8 <register_tm_clones+0x38>
275 10f0: ff e0 jmpq *%rax
276 10f2: 66 0f 1f 44 00 00 nopw 0x0(%rax,%rax,1)
277 10f8: c3 retq
278 10f9: 0f 1f 80 00 00 00 00 nopl 0x0(%rax)
2790000000000001100 <__do_global_dtors_aux>:
280__do_global_dtors_aux():
281 1100: f3 0f 1e fa endbr64
282 1104: 80 3d 05 2f 00 00 00 cmpb $0x0,0x2f05(%rip) # 4010 <__TMC_END__>
283 110b: 75 2b jne 1138 <__do_global_dtors_aux+0x38>
284 110d: 55 push %rbp
285 110e: 48 83 3d e2 2e 00 00 cmpq $0x0,0x2ee2(%rip) # 3ff8 <__cxa_finalize@GLIBC_2.2.5>
286 1115: 00
287 1116: 48 89 e5 mov %rsp,%rbp
288 1119: 74 0c je 1127 <__do_global_dtors_aux+0x27>
289 111b: 48 8b 3d e6 2e 00 00 mov 0x2ee6(%rip),%rdi # 4008 <__dso_handle>
290 1122: e8 19 ff ff ff callq 1040 <__cxa_finalize@plt>
291 1127: e8 64 ff ff ff callq 1090 <deregister_tm_clones>
292 112c: c6 05 dd 2e 00 00 01 movb $0x1,0x2edd(%rip) # 4010 <__TMC_END__>
293 1133: 5d pop %rbp
294 1134: c3 retq
295 1135: 0f 1f 00 nopl (%rax)
296 1138: c3 retq
297 1139: 0f 1f 80 00 00 00 00 nopl 0x0(%rax)
2980000000000001140 <frame_dummy>:
299frame_dummy():
300 1140: f3 0f 1e fa endbr64
301 1144: e9 77 ff ff ff jmpq 10c0 <register_tm_clones>
3020000000000001149 <func>:
303func():
304 1149: f3 0f 1e fa endbr64
305 114d: 55 push %rbp
306 114e: 48 89 e5 mov %rsp,%rbp
307 1151: 8b 05 c1 2e 00 00 mov 0x2ec1(%rip),%eax # 4018 <l_count.2316>
308 1157: 83 c0 01 add $0x1,%eax
309 115a: 89 05 b8 2e 00 00 mov %eax,0x2eb8(%rip) # 4018 <l_count.2316>
310 1160: 8b 05 ae 2e 00 00 mov 0x2eae(%rip),%eax # 4014 <g_count>
311 1166: 83 c0 01 add $0x1,%eax
312 1169: 89 05 a5 2e 00 00 mov %eax,0x2ea5(%rip) # 4014 <g_count>
313 116f: 8b 15 9f 2e 00 00 mov 0x2e9f(%rip),%edx # 4014 <g_count>
314 1175: 8b 05 9d 2e 00 00 mov 0x2e9d(%rip),%eax # 4018 <l_count.2316>
315 117b: 89 c6 mov %eax,%esi
316 117d: 48 8d 3d 80 0e 00 00 lea 0xe80(%rip),%rdi # 2004 <_IO_stdin_used+0x4>
317 1184: b8 00 00 00 00 mov $0x0,%eax
318 1189: e8 c2 fe ff ff callq 1050 <printf@plt>
319 118e: 90 nop
320 118f: 5d pop %rbp
321 1190: c3 retq
3220000000000001191 <util_func>:
323util_func():
324 1191: f3 0f 1e fa endbr64
325 1195: 55 push %rbp
326 1196: 48 89 e5 mov %rsp,%rbp
327 1199: 48 83 ec 10 sub $0x10,%rsp
328 119d: 89 7d fc mov %edi,-0x4(%rbp)
329 11a0: 8b 45 fc mov -0x4(%rbp),%eax
330 11a3: 89 c6 mov %eax,%esi
331 11a5: 48 8d 3d 72 0e 00 00 lea 0xe72(%rip),%rdi # 201e <_IO_stdin_used+0x1e>
332 11ac: b8 00 00 00 00 mov $0x0,%eax
333 11b1: e8 9a fe ff ff callq 1050 <printf@plt>
334 11b6: 90 nop
335 11b7: c9 leaveq
336 11b8: c3 retq
33700000000000011b9 <main>:
338main():
339 11b9: f3 0f 1e fa endbr64
340 11bd: 55 push %rbp
341 11be: 48 89 e5 mov %rsp,%rbp
342 11c1: b8 00 00 00 00 mov $0x0,%eax
343 11c6: e8 7e ff ff ff callq 1149 <func>
344 11cb: b8 00 00 00 00 mov $0x0,%eax
345 11d0: e8 74 ff ff ff callq 1149 <func>
346 11d5: b8 00 00 00 00 mov $0x0,%eax
347 11da: e8 6a ff ff ff callq 1149 <func>
348 11df: bf 0a 00 00 00 mov $0xa,%edi
349 11e4: e8 a8 ff ff ff callq 1191 <util_func>
350 11e9: e8 07 00 00 00 callq 11f5 <test_func>
351 11ee: b8 00 00 00 00 mov $0x0,%eax
352 11f3: 5d pop %rbp
353 11f4: c3 retq
35400000000000011f5 <test_func>:
355test_func():
356 11f5: f3 0f 1e fa endbr64
357 11f9: 55 push %rbp
358 11fa: 48 89 e5 mov %rsp,%rbp
359 11fd: 90 nop
360 11fe: 5d pop %rbp
361 11ff: c3 retq
3620000000000001200 <__libc_csu_init>:
363__libc_csu_init():
364 1200: f3 0f 1e fa endbr64
365 1204: 41 57 push %r15
366 1206: 4c 8d 3d ab 2b 00 00 lea 0x2bab(%rip),%r15 # 3db8 <__frame_dummy_init_array_entry>
367 120d: 41 56 push %r14
368 120f: 49 89 d6 mov %rdx,%r14
369 1212: 41 55 push %r13
370 1214: 49 89 f5 mov %rsi,%r13
371 1217: 41 54 push %r12
372 1219: 41 89 fc mov %edi,%r12d
373 121c: 55 push %rbp
374 121d: 48 8d 2d 9c 2b 00 00 lea 0x2b9c(%rip),%rbp # 3dc0 <__do_global_dtors_aux_fini_array_entry>
375 1224: 53 push %rbx
376 1225: 4c 29 fd sub %r15,%rbp
377 1228: 48 83 ec 08 sub $0x8,%rsp
378 122c: e8 cf fd ff ff callq 1000 <_init>
379 1231: 48 c1 fd 03 sar $0x3,%rbp
380 1235: 74 1f je 1256 <__libc_csu_init+0x56>
381 1237: 31 db xor %ebx,%ebx
382 1239: 0f 1f 80 00 00 00 00 nopl 0x0(%rax)
383 1240: 4c 89 f2 mov %r14,%rdx
384 1243: 4c 89 ee mov %r13,%rsi
385 1246: 44 89 e7 mov %r12d,%edi
386 1249: 41 ff 14 df callq *(%r15,%rbx,8)
387 124d: 48 83 c3 01 add $0x1,%rbx
388 1251: 48 39 dd cmp %rbx,%rbp
389 1254: 75 ea jne 1240 <__libc_csu_init+0x40>
390 1256: 48 83 c4 08 add $0x8,%rsp
391 125a: 5b pop %rbx
392 125b: 5d pop %rbp
393 125c: 41 5c pop %r12
394 125e: 41 5d pop %r13
395 1260: 41 5e pop %r14
396 1262: 41 5f pop %r15
397 1264: c3 retq
398 1265: 66 66 2e 0f 1f 84 00 data16 nopw %cs:0x0(%rax,%rax,1)
399 126c: 00 00 00 00
4000000000000001270 <__libc_csu_fini>:
401__libc_csu_fini():
402 1270: f3 0f 1e fa endbr64
403 1274: c3 retq
404Disassembly of section .fini:
4050000000000001278 <_fini>:
406_fini():
407 1278: f3 0f 1e fa endbr64
408 127c: 48 83 ec 08 sub $0x8,%rsp
409 1280: 48 83 c4 08 add $0x8,%rsp
410 1284: c3 retq
1test_a.c
2static int test_func_in_a(int a)
3{
4 return a + 1;
5}
6int test_func_in_a_ex(int a)
7{
8 return test_func_in_a(a);
9}
10----------------------------
11test_b.c
12int test_func_in_b(void)
13{
14 int a = 1;
15 int b;
16 //call test_func_in_a function fail because of "static"
17 //b = test_func_in_a(a)
18 //call test_func_in_a_ex function ok without "static"
19 b = test_func_in_a_ex(a)
20 return b;
21}
原文:https://club.rt-thread.org/ask/article/1b38085300b58f82.html
作者:recan
———————End———————
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