[SOLVED] Linker and undefined function references

[luiscubal]

Just for testing, I came up with this sample Asm/C program:

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segment .data

segment .bss

segment .text
	global happy
happy:
	push ebp
	mov ebp, esp
	
	mov eax, 5

	pop ebp
	ret

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#include <stdio.h>

extern long happy();

int main(){
	printf("I got: %d\n", happy());

	return 0;
}

And compiling it with

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nasm test.asm -o test.o -f elf32
gcc -m32 main.c test.o -o experiment

works perfectly...

However,

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segment .data

segment .bss

segment .text

	extern global_var
	global happy
happy:
	push ebp
	mov ebp, esp
	
	mov eax, 5
	add eax, [global_var]

	pop ebp
	ret

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#include <stdio.h>

extern long happy();

int global_var = 3;

int main(){
	printf("I got: %d\n", happy());

	return 0;
}

does not, due to: "test.asm:(.text+0xa): undefined reference to `global_var'"...

I think I'm missing something about C-assembly interoperability...

[Combuster]

objdump? -fno-leading-underscores? The reason the first example works is because there are zero references to other files.

[luiscubal]

weird. Now I tried the exact same file and the same command and it worked.
I don't understand. I used the exact same commands and this time it worked... I wonder what happened the first time...
(the assembly test, not the kernel)

[luiscubal]

I asked someone else that was also making a kernel and he sent me his hello world kernel.
I've replaced my assembly and linker script by his. Although they look very similar(nearly identical), his seems to work. I'm not sure what happened here but I'm glad it's solved.

[Solar]

I'm not sure what happened here but I'm glad it's solved.

It's not "solved" until you understand it..-