I am using gcc compiler in windows10's powershell. gcc came with the 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.
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.
Meanwhile I do not get this linker error if I use arm-atollic-eabi-gcc or gcc running on ubuntu.
Here is a simple code to demonstrate this:
hello.c:
#include "weak.h"
void whatever(void)
{
iamweak();
}
weak.c:
#include <stdio.h>
#include "weak.h"
void __attribute__((weak)) iamweak(void)
{
printf("i am weak...\n");
}
weak.h
void iamweak(void);
main.c
int main(void)
{
return 0;
}
Creating the object files and linking:
> gcc -c main.c weak.c hello.c
> 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
Now I checked with gcc-nm the symbol table of hello.o:
> gcc-nm hello.o
00000000 b .bss
00000000 d .data
00000000 r .eh_frame
00000000 r .rdata$zzz
00000000 t .text
U _iamweak
00000000 T _whatever
Symbol table for weak.o:
>gcc-nm weak.o
00000000 b .bss
00000000 d .data
00000000 r .eh_frame
00000000 r .rdata
00000000 r .rdata$zzz
00000000 t .text
00000000 T .weak._iamweak.
w _iamweak
U _puts
Now when I use gcc on Ubuntu as I said everything works. Also the symbol tables are a little different.
Symbol table for hello.o:
nm hello.o
U _GLOBAL_OFFSET_TABLE_
U iamweak
0000000000000000 T whatever
Symbol table for weak.o:
nm weak.o
U _GLOBAL_OFFSET_TABLE_
0000000000000000 W iamweak
U puts
From https://linux.die.net/man/1/nm it says that "If lowercase, the symbol is local; if uppercase, the symbol is global (external)."
So iamweak is local in windows10 and global in Ubuntu. Is that why the linker cannot see it? What can I do about this? The weak function definitions are also in some HAL libraries and I don't want to modify those. Is there a workaround?
