mixed linker?

[nekros]

Would this even be possible to write a linker that could link 64bit and 32bit object files?

elf32 + elf64 -> elf32 || elf64

[JohnnyTheDon]

Not sure... but I do link my elf64 object files into an elf32 for my multiboot bootloader. It hasn't given me any trouble.

[nekros]

what linker do you use? ld won't do that...

[JohnnyTheDon]

GNU ld. Works fine with a linker script.

Here's an excerpt from mine:

OUTPUT_FORMAT(elf32-i386)
OUTPUT_ARCH(i386:x86-64)

I can even put 32-bit assembly code in there (and 16-bit with some tweaks).

[nekros]

Awesome, could this be used as a technique to do boot a kernel with grub? I might want to add this to add this to the wiki...

[JohnnyTheDon]

I guess so. The one problem I can see is that everything has to be identity mapped. This isn't a problem for a bootloader, but a long mode kernel would usually be loaded in the higher half, and grub won't be about to do that (unless you have memory up to 0xFFFF800000000000). The only reason I bother with elf64 -> elf32 instead of elf32 -> elf32 in my bootloader is that 64-bit C code needs to be compiled to elf64.

[nekros]

My kernel is not higher half, so it works for me. I'm gonna attempt it right now so let's see what happens.

[nekros]

Oh, this is just converting a 64 bit to 32 bit elf not mixed linking?

[JohnnyTheDon]

I was linking a series of elf64 files into an elf32 using ld. No objcopy or anything like that. You might be able to link elf64 and elf32 files together by doing it in 3 stages: link the elf32s into one relocatable elf32 file, link the elf64s into one relocatable elf32 file, then link the two relocatable elf32s into another elf32.