[英]gcc weak attribute inconsistent behaviour
I am using gcc compiler in windows10's powershell.我在 windows10 的 powershell 中使用 gcc 编译器。 gcc came with the Atollic TrueSTUDIO ide.
gcc 带有 Atollic TrueSTUDIO ide。 The reason I am doing this is to be able to create an .exe file from the C code so unit testing becomes easier.
我这样做的原因是能够从 C 代码创建一个 .exe 文件,以便单元测试变得更容易。
I encounter a linker error (undefined reference to 'function_name') when there is a function that is defined as weak and that function is used in another .c file.当有一个函数被定义为弱函数并且该函数在另一个 .c 文件中使用时,我遇到了链接器错误(对“function_name”的未定义引用)。
Meanwhile I do not get this linker error if I use arm-atollic-eabi-gcc or gcc running on ubuntu.同时,如果我使用在 ubuntu 上运行的 arm-atollic-eabi-gcc 或 gcc,则不会出现此链接器错误。
Here is a simple code to demonstrate this:这是一个简单的代码来演示这一点:
hello.c:你好ç:
#include "weak.h"
void whatever(void)
{
iamweak();
}
weak.c:弱c:
#include <stdio.h>
#include "weak.h"
void __attribute__((weak)) iamweak(void)
{
printf("i am weak...\n");
}
weak.h弱.h
void iamweak(void);
main.c主文件
int main(void)
{
return 0;
}
Creating the object files and linking:创建目标文件并链接:
> gcc -c main.c weak.c hello.c
> gcc -c main.c weak.c hello.c
> gcc -o main.exe main.o weak.o hello.o
> gcc -o main.exe main.o weak.o hello.o
> hello.o:hello.c:(.text+0x7): undefined reference to `iamweak' collect2.exe: error: ld returned 1 exit status
> hello.o:hello.c:(.text+0x7): 未定义对 `iamweak' collect2.exe 的引用:错误:ld 返回 1 退出状态
Now I checked with gcc-nm the symbol table of hello.o:现在我用 gcc-nm 检查了 hello.o 的符号表:
> gcc-nm hello.o
> gcc-nm hello.o
00000000 b .bss
00000000 b.bss
00000000 d .data
00000000 d .data
00000000 r .eh_frame
00000000 r .eh_frame
00000000 r .rdata$zzz
00000000 r .rdata$zzz
00000000 t .text
00000000 吨.text
U _iamweak
U_iamweak
00000000 T _whatever
00000000 T _whatever
Symbol table for weak.o: weak.o 的符号表:
>gcc-nm weak.o
>gcc-nm 弱.o
00000000 b .bss
00000000 b.bss
00000000 d .data
00000000 d .data
00000000 r .eh_frame
00000000 r .eh_frame
00000000 r .rdata
00000000 r .rdata
00000000 r .rdata$zzz
00000000 r .rdata$zzz
00000000 t .text
00000000 吨.text
00000000 T .weak._iamweak.
00000000 T .weak._iamweak。
w _iamweak
w _iamweak
U _puts
U_puts
Now when I use gcc on Ubuntu as I said everything works.现在,当我在 Ubuntu 上使用 gcc 时,就像我说的那样一切正常。 Also the symbol tables are a little different.
符号表也有点不同。
Symbol table for hello.o: hello.o 的符号表:
nm hello.o
纳米你好.o
U _GLOBAL_OFFSET_TABLE_
你_GLOBAL_OFFSET_TABLE_
U iamweak
弱
0000000000000000 T whatever
0000000000000000 T 随便
Symbol table for weak.o: weak.o 的符号表:
nm weak.o
纳米弱
U _GLOBAL_OFFSET_TABLE_
你_GLOBAL_OFFSET_TABLE_
0000000000000000 W iamweak
0000000000000000 W iamweak
U puts
看跌期权
From https://linux.die.net/man/1/nm it says that "If lowercase, the symbol is local; if uppercase, the symbol is global (external)."从https://linux.die.net/man/1/nm它说“如果小写,符号是本地的;如果大写,符号是全局的(外部)。”
So iamweak is local in windows10 and global in Ubuntu.所以 iamweak 在 windows10 中是本地的,在 Ubuntu 中是全局的。 Is that why the linker cannot see it?
这就是链接器看不到它的原因吗? What can I do about this?
我该怎么办? The weak function definitions are also in some HAL libraries and I don't want to modify those.
弱函数定义也在一些 HAL 库中,我不想修改它们。 Is there a workaround?
有解决方法吗?
it is atollic gcc fork error.这是 atollic gcc fork 错误。 It does even worse:
更糟糕的是:
main:
00401440: push %ebp
00401441: mov %esp,%ebp
00401443: and $0xfffffff0,%esp
00401446: call 0x401970 <__main>
36 iamweak();
0040144b: call 0x0
37 return 0;
00401450: mov $0x0,%eax
38 }
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