Linking error

[abachler]

Im using GCC and getting an error linking,

loader.o: In function 'loader':
loader.s: (.text+0x14): undefined reference to 'kmain'

here are the source files -

loader.s (asm)

global loader ; making entry point visible to linker
extern kmain ; kmain is defined in kernel.o
; setting up the Multiboot header
MODULEALIGN equ 1<<0 ; align loaded modules on page boundaries
MEMINFO equ 1<<1 ; provide memory map
FLAGS equ MODULEALIGN | MEMINFO ; this is the Multiboot 'flag' field
MAGIC equ 0x1BADB002 ; 'magic number' lets bootloader find the header
CHECKSUM equ -(MAGIC + FLAGS) ; checksum required
section .text
align 4
MultiBootHeader:
dd MAGIC
dd FLAGS
dd CHECKSUM
; reserve initial kernel stack space
STACKSIZE equ 0x4000 ; that's 16k.
loader:
mov esp, stack+STACKSIZE ; set up the stack
push eax ; pass Multiboot magic number
push ebx ; pass Multiboot info structure
call kmain ; call kernel proper
hlt ; halt machine should kernel return
section .bss
align 32
stack:
resb STACKSIZE ; reserve 16k stack on a quadword boundary

kernel.cpp

void kmain(void* mbd, unsigned int magic){
// this is to stop compiler warnigns durign development
mbd;
magic;
}

my linker file

ENTRY (loader)
SECTIONS{
. = 0x00100000;
.text :{
*(.text)
}
.rodata ALIGN (0x1000) : {
*(.rodata)
}
.data ALIGN (0x1000) : {
*(.data)
}
.bss : {
sbss = .;
*(COMMON)
*(.bss)
ebss = .;
}
}

and my link sequence

nasm -f elf -o loader.o loader.s  
gcc -o kernel.o -c kernel.cpp -Wall -Wextra -Werror -nostdlib -nostartfiles -nodefaultlibs  
ld -T linker.ld -o kernel.bin kernel.o loader.o

[Salem]

If you do
nm kernel.o
You'll find that your kmain has been name-decorated because you named it .cpp

[abachler]

:bow:

yes that was it, although it did the same thing when I compiled it as .c

its now named __Z5kmainv

so I updated the extern and call lines and it linked just fine now

now to test it out

[Salem]

You did something wrong if it's still decorated after compiling it as a .c file.

[abachler]

You did something wrong if it's still decorated after compiling it as a .c file.

Turns out I was using the wrong compiler, I was trying to compile for an ELF target, and i was using the MinGW version of GCC. After I built a cross compiler it worked fine.