为什么共享库的符号在链接时未解析？ [英] Why symbols of a shared library are not resolved at link time?

问题描述

这是我在这个网站上的第二篇文章，我努力理解与gcc的编译/链接过程。当我尝试制作可执行文件时，需要在链接时解析符号，但是当我尝试创建共享库时，符号在链接时不会解析。它们可能会在我试图使用此共享库来创建可执行文件时解决。动手：

This is my 2nd post on this site in my effort to understand the compilation/linking process with gcc. When I try to make an executable, symbols need to be resolved at link time, but when I try to make a shared library, symbols are not resolved at link time of this library. They will perhaps be resolved when I am trying to make an executable using this shared library. Hands-on:

bash$ cat printhello.c
#include <stdio.h>
//#include "look.h"

void PrintHello()
{
look();
printf("Hello World\n");
}

bash$ cat printbye.c
#include <stdio.h>
//#include "look.h"

void PrintBye()
{
look();
printf("Bye bye\n");
}

bash$  cat look.h
void look();

bash$ cat look.c
#include <stdio.h>

void look()
{
printf("Looking\n");
}

bash$ gcc printhello.c printbye.c
/usr/lib/gcc/i386-redhat-linux/4.1.2/../../../crt1.o: In function `_start':
(.text+0x18): undefined reference to `main'
/tmp/cck21S0u.o: In function `PrintHello':
printhello.c:(.text+0x7): undefined reference to `look'
/tmp/ccNWbCnd.o: In function `PrintBye':
printbye.c:(.text+0x7): undefined reference to `look'
collect2: ld returned 1 exit status

bash$ gcc -Wall -shared -o libgreet printhello.c printbye.c
printhello.c: In function 'PrintHello':
printhello.c:6: warning: implicit declaration of function 'look'
printbye.c: In function 'PrintBye':
printbye.c:5: warning: implicit declaration of function 'look'

所以我的问题是当我链接共享图书馆。这个工作（解析其下游的符号）将需要做，当我将使用这个库来做一个可执行文件，但这意味着我们需要知道这个库依赖于使用这个库，但这不是不可取的吗？

So my question is why are symbols not resolved when I am linking a shared library. This work(Resolving symbols of its downstream) will need to be done when I will use this library to make an executable, but that means we need to know what this library depends on when using this library, but isn't it not undesirable?

感谢，
Jagrati

Thanks, Jagrati

推荐答案

code> -z defs 当构建库做你想要什么？如果没有，检查ld手册页，有很多选项处理未定义的符号。

Does adding -z defs when building the library do what you want? If not, check the ld man pages, there are quite a few options on the handling of undefined symbols.

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