我在理解由C源文件编译的重定位表条目时遇到了一些问题。 我的程序如下:
//a.c
extern int shared;
int main(){
int a = 100;
swap(&a, &shared);
a = 200;
shared = 1;
swap(&a, &shared);
}
//b.c
int shared = 1;
void swap(int* a, int* b) {
if (a != b)
*b ^= *a ^= *b, *a ^= *b;
}
我使用以下命令编译和链接它们:gcc -c -fno-stack-protector a.c b.c
和 ld a.o b.o -e main -o ab
。
然后我使用 objdump -r a.o
命令来检查其重定位表。
RELOCATION RECORDS FOR [.text]:
OFFSET TYPE VALUE
0000000000000014 R_X86_64_32 shared
0000000000000021 R_X86_64_PC32 swap-0x0000000000000004
000000000000002e R_X86_64_PC32 shared-0x0000000000000008
000000000000003b R_X86_64_32 shared
0000000000000048 R_X86_64_PC32 swap-0x0000000000000004
< p > a.o
的反汇编结果是
Disassembly of section .text:
0000000000000000 <main>:
0: 55 push %rbp
1: 48 89 e5 mov %rsp,%rbp
4: 48 83 ec 10 sub $0x10,%rsp
8: c7 45 fc 64 00 00 00 movl $0x64,-0x4(%rbp)
f: 48 8d 45 fc lea -0x4(%rbp),%rax
13: be 00 00 00 00 mov $0x0,%esi
18: 48 89 c7 mov %rax,%rdi
1b: b8 00 00 00 00 mov $0x0,%eax
20: e8 00 00 00 00 callq 25 <main+0x25>
25: c7 45 fc c8 00 00 00 movl $0xc8,-0x4(%rbp)
2c: c7 05 00 00 00 00 01 movl $0x1,0x0(%rip) # 36 <main+0x36>
33: 00 00 00
36: 48 8d 45 fc lea -0x4(%rbp),%rax
3a: be 00 00 00 00 mov $0x0,%esi
3f: 48 89 c7 mov %rax,%rdi
42: b8 00 00 00 00 mov $0x0,%eax
47: e8 00 00 00 00 callq 4c <main+0x4c>
4c: b8 00 00 00 00 mov $0x0,%eax
51: c9 leaveq
52: c3 retq
我的问题是:在14处和2e处的
shared
完全是相同的对象。为什么它们有不同的符号名称?