linking problem: i386:x86-64 architecture of input file *.o is incompatible with i386 output

Question

I got a problem in linking when I moved my osdev to linux where it worked previously on gcc 3.5.* and binutils 2.18 (compiled to output x86_64-elf) running under cygwin.

Here are the infos:

gcc -v

Using built-in specs.
Target: i686-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu/Linaro 4.4.4-14ubuntu5' --with-bugurl=file:///usr/share/doc/gcc-4.4/README.Bugs --enable-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr --program-suffix=-4.4 --enable-shared --enable-multiarch --enable-linker-build-id --with-system-zlib --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.4 --libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug --enable-objc-gc --enable-targets=all --disable-werror --with-arch-32=i686 --with-tune=generic --enable-checking=release --build=i686-linux-gnu --host=i686-linux-gnu --target=i686-linux-gnu
Thread model: posix
gcc version 4.4.5 (Ubuntu/Linaro 4.4.4-14ubuntu5) 

ld -v

GNU ld (GNU Binutils for Ubuntu) 2.20.51-system.20100908

part of ld -help

....

ld: supported targets: elf32-i386 a.out-i386-linux pei-i386 elf32-little elf32-big elf64-x86-64 pei-x86-64 elf64-l1om elf64-little elf64-big plugin srec symbolsrec verilog tekhex binary ihex trad-core

....

The code:

main.c

void main(){

    /**some code here**/

}

start.asm

[bits 64]

global start

extern main

start:

call main

link.ld

OUTPUT_FORMAT(elf64-x86-64);

offset = 0x1000000;

ENTRY(start);

SECTIONS{

    . = offset;

    .text : AT(ADDR(.text) - offset){

        _code = .;

        *(.text)

        (.rodata)

        . = ALIGN(4096);}

   .data : AT(ADDR(.data) - offset){

        _data = .;

        *(.data)

        . = ALIGN(4096);}

   .bss : AT(ADDR(.bss) - offset){

       _bss = .;

       *(.bss)

       *(COMMON)

       . = ALIGN(4096);}

   _end = .;

   /DISCARD/ :

   {*(.comment)}

}

build.sh

nasm -f elf64 -o start.o start.asm

echo .

echo .

echo .

gcc -m64 -ffreestanding -nostdlib -mno-red-zone -mno-mmx -mno-sse -mno-sse2 -mno-sse3 -mno-3dnow -c -o main.o main.c

echo .

echo .

echo .

ld -nostdlib -nodefaultlibs -T link.ld -o out.elf start.o main.o

terminal output

.

.

.

.

.

.

ld: i386:x86-64 architecture of input file 'start.o' is incompatible with i386 output

ld: i386:x86-64 architecture of input file 'main.o' is incompatible with i386 output

I don't understand why it displays 'incompatible with i386 output' when there's OUTPUT_FORMAT(elf64-x86-64); in my linker script specifying the targeted output..

Solution

Try this:

LDEMULATION="elf_x86_64"
ld -nostdlib -nodefaultlibs -T link.ld -o out.elf start.o main.o