.bss vs COMMON:什么去哪儿了? [英] .bss vs COMMON: what goes where?

问题描述

从我的书中:

.bss:

未初始化的全局 C 变量

Uninitialized global C variables

常见:

尚未分配的未初始化数据对象

Uninitalized data objects that are not yet allocated

我不得不说，我看不出明显的区别.我什至不太明白什么是未初始化、未分配的数据对象……似乎什么都没有.我使用 GNU 的 readelf 工具尝试查看一些简单的 C 代码，但找不到单个 COMMON 符号.我读过诸如 FORTRAN 的 COMMON 类型是 COMMON 符号的示例之类的东西 - 但我不知道 FORTRAN

I have to say, I don't quite see a clear distinction. I don't even quite understand what an uninitizalied, non-allocated data object is...seems like nothing. I've used GNU's readelf tool to try to take a look at some simple C code, but can't find a single COMMON symbol. I've read things like FORTRAN's COMMON type is an example of a COMMON symbol - but I don't know FORTRAN

谁能帮我区分这两者?如果可能的话，希望有一个 C 示例?非常感谢.

Can someone possibly distinguish the two for me? If at all possible, hopefully with a C example? Greatly appreciated.

编辑:来自 这个 在这里发布变量 c:

edit: from this post, the variable c here:

int c;
int main() {} ...

应该是常见的.但是使用 objdump -t 显示 c 在 .bss...

should be COMMON. But using objdump -t shows for me that c is in .bss...

困惑

推荐答案

// file a.c
// file-scope

int a = 0;  // goes into BSS

a.c编译成目标文件a.o后，a符号进入BSS部分.

after compilation of a.c into object file a.o, a symbol goes into BSS section.

// file b.c
// file-scope

int b;  // goes into COMMON section

b.c编译成目标文件b.o后，b符号进入COMMON段.

after compilation of b.c into object file b.o, b symbol goes into COMMON section.

a.o 和 b.o 链接后​​，a 和 b 符号都进入 BSS 部分.通用符号只存在于目标文件中，不存在于可执行文件中.Unix 中 COMMON 符号的思想是在特定条件下允许在单个公共符号下对同一变量(在不同编译单元中)进行多个外部定义.

After linking of a.o and b.o, both a and b symbols goes into BSS section. Common symbols only exist in object files, not in executable files. The idea of COMMON symbols in Unix is to allow multiple external definitions of a same variable (in different compilation units) under a single common symbol under certain conditions.

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