moving code from c to C++ gives linker error

[bartexsz]

I am learning OS developmebt from JamesM's kernel development tutorial.

Recently i decided to rewite screen handling as object. Unfortunately i can't now link it, linker gives me:

Code: Select all

main.o: In function `main':
main.cpp:(.text+0x7e): undefined reference to `_Unwind_Resume'
main.o:(.eh_frame+0x13): undefined reference to `__gxx_personality_v0'

My makefile:

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SOURCES=boot.o main.o common.o screen.o

CPPFLAGS=-nostdlib -nostdinc -fno-builtin -fno-stack-protector
LDFLAGS=-Tlink.ld
ASFLAGS=-felf

all: $(SOURCES) link 

clean:
	-rm *.o kernel

link:
	ld $(LDFLAGS) -o kernel $(SOURCES)

.asm.o:
	nasm $(ASFLAGS) $<

link.ld

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OUTPUT_FORMAT("binary")
ENTRY(start)
SECTIONS
{
    .text 0x100000 :
    {
    code = .; _code = .; __code = .;
    *(.text)
    . = ALIGN(4096);
    }

    .data :
    {
    data = .; _data = .; __data = .;
    *(.data)
    . = ALIGN(4096);
    }
    
    .bss :
    {
    bss = .; _bss = .; __bss = .;
    *(.bss)
    . = ALIGN(4096);
    }

    end = .; _end = .; __end = .;
}

[xenos]

You probably wish to disable exception handling: C++ Bare Bones

[Combuster]

Nor are you using the GCC Cross-Compiler

[bartexsz]

Thanks for help , i had to simply add extern "C" to main function, as in c++ Bare Bones

EDIT: It was enough , but only for main. I started implementing gdt, and these errors are back.
I tried to use gcc-cross compiler, but I don't know how to put $TARGET to makefile to make it works.

EDIT2: Ok, I added -ffreestanding , now it works, however, now i get:

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boot.o main.o common.o screen.o gdt_entry.o descrtables.o gdtptr.o link
make: boot.o: Command not found

It worked earlier. What can be wrong?

[invalid]

You forgot $(CC) in your Makefile and it tries executing "boot.o"?

[bartexsz]

Ok, thx.

One more question, how can I implement c++ class method in external asm file?

[bartexsz]

thx, I used g++ with -S parameter to find mangled name. Is there any way to force compiler to not mangle name?

[brain]

Yes. extern "C" void funcname() { }

[bartexsz]

It doesn't work for functions which belongs to class

[bluemoon]

To access class member you either dirty hack the mangling/ABI or write an extern C wrapper function. Either way it is not elegant, and the need to access class member in assembly is usually due to unnecessary optimization or design problem.

We have a thread talk about this recently.

[bartexsz]

Not all can be implemented in C++

Actualy it is GDT implementation, in which now works all, but flushing. Unfortunately flushing hangs all.

If someone could check this, here is my github project: https://github.com/bartexsz/Freeq-OS

descrtables.cpp contains function in which i'm calling flush() and gdt.asm implemetation of this function

[bluemoon]

As berkus mentioned, you either call assembly function from C++ member, or if speed is critical you do inline assembly.

By hacking into mangling you lock yourself into a specific compiler, and do not surprise if your code breaks on next year's gcc.

[Owen]

If you're willing to use a GCC extension, you can define the symbol name using the 'asm("SymbolName")' directive

[bartexsz]

I forgot to say, I solved compiling/linkage error. My only problem now is flushing which hangs all, despite fact that it's called nearly exactly like in JamesM's kernel development tutorial, what shows my code on github. (Link in my previous post).